s- Block Elements

37s- Block Elements

MH - CET Chemistry - XI

10.s- Block Elements

10.0 : Prominent Scientists

10.1 : General introduction

Q.1. State modern periodic law.

Ans: Modern periodic law states that,"the physical and chemical properties of the elements are periodic function

of their atomic numbers ".

Q.2. Why are the elements in the long form of periodic table called s-block, p-block, d-block or f-block

elements?

Ans: i) The long form of the periodic table is based on the modem periodic law.

ii) It is divided into four blocks (s, p, d, f) based on the subshell (s, p, d, f) into which the last/differentiating

electron enters.

iii) If the electron enters the s-subshell, the element is in s-block and so it is called s-block element.

Similarly, the corresponding elements in their respective blocks are therefore called p-block, d-block,

f-block elements.

Q.3. What are s-block elements? Explain the position of s-block elements in periodic table.

Ans: i) In the long form of periodic table, elements in which the last electron in an atom enters the outermost

's' orbital are called 's' block elements.

ii) Since the s-orbital can accommodate a maximum of 2 electrons, it consists of two groups namely

group-I (alkali metals) and group-2 (alkaline earth metals).

iii) Atoms of group-I (with one valence electron) and group-2 (with two valence electrons) are characterized

by the general electronic configuration: ns' and ns2 respectively.

iv) s-block elements are placed on the extreme left hand side of the long form of the periodic table.

v) They are collectively called as normal elements or representative elements.

Scientists

Sir Humphry Davy (1778 - 1829)

(English chemist)

Arthur H. Crompton (1892 - 1962)

(American physicist)

Contributions

i. Remembered for his discoveries of several alkali and

alkaline earth metals.

ii. Contributed in the discoveries of the elemental

nature of chlorine and iodine.

iii. Invented Davy lamp which allowed miners to enter mines.

iv. Pioneer in the field of electrolysis using the battery to

split up common compounds and prepared many new

elements.

v. Discovered magnesium, boron, barium and potassium

from caustic potash.

vi. Isolated elements by electrolysis like potassium (which

was first metal isolated by him), sodium (which was

isolated by him by electrolyzing molten sodium

hydroxide).

i. Proved wave particle duality through his research on X-rays.

ii. Did original work on sodium vapour lamp.

iii. Developed instrumentation of an aircraft. Received

iv. Nobel prize in physics in 1927.

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38s- Block Elements


Q.4. Why are the elements of group-1 called alkali metals?

Ans: i) Hydrogen (Z = 1), Lithium (Z = 3), Sodium (Z = 11), Potassium (Z = 19), Rubidium (Z = 37),

Caesium (Z = 55) and Francium (Z = 87) together constitute group-I.

ii) Oxides and hydroxides of group-l elements on combining with water form water soluble bases i.e.,

alkali. Hence, elements of group-I are called as 'alkali metals' .

eg. Na2O + H

2O 2NaOH

iii) The word 'alkali' is derived from arabic word 'alquis' meaning 'plant ashes' which are rich in the

carbonates of sodium and potassium.

Q.5. As per recent trend hydrogen is placed at the top of the periodic table and not in the group 1, why?

Ans: i) Hydrogen has atomic number 1 and electronic configuration ls1.

ii) It resembles alkali metals having the electronic configuration ns', with respect to the formation of

unipositive ions and formation of oxides, halides and sulphides.

iii) Alkali metals have low ionisation enthalpy, thus, in terms of ionization enthalpy, hydrogen (which has a

very high ionisation enthalpy) resembles more with halogens.

iv) Hydrogen is gaseous while all other elements of group 1 are solids.

v) Also, hydrogen does not possess metallic character under normal conditions unlike the alkali metals

which exhibit metallic character.

vi) Hydrogen also resembles halogens.

eg. It forms anion H– like halides, diatomic molecule H2, covalent compounds, etc.

vii) Hydrogen is very less reactive as compared to halogens.

viii) Thus, hydrogen resembles both the alkali metals and the halogens, though in case of certain properties,

it also differs from them.

ix) This unique behaviour of hydrogen makes its position in the periodic table controversial or anomalous.

x) Therefore, hydrogen is best placed separately at the top of the periodic table.

Q.6. Give reasons: Alkaline earth metals do not occur in free state.

Ans: Alkaline earth metals have two valence electrons which can be lost easily during a reaction. Hence, alkaline



39s- Block Elements


earth metals are highly reactive and do not occur in free state.

Q.7. Write the electronic configuration of alkali and alkaline earth metals.

Ans: i) In alkali and alkaline earth metals, the last electron (differentiating electron) enters the ns orbital of the

atom.

ii) Thus, the general electronic configuration of outermost shell of elements of group 1 and group 2 are

ns1 and ns2 respectively, where 'n' represents the valence shell.

iii) The elements belonging to group 1 of the periodic table and their electronic configurations are given

below. (Except hydrogen, remaining elements are alkali metals).

iv) The elements belonging to group 2 of the periodic table and their electronic configuration are given

below:

10.2 : Occurrence

Q.8. Write a brief note on the occurrence of s-block elements.

Ans: s-block elements of the periodic table consists of two groups: Group-l (Alkali metals) and Group-2

(Alkaline earth metals).

i) Alkali Metals :

Electronic con-

figuration

Valence shell

electronic

configuration

(ns1)

Period Element Symbol Atomic

Number

1 Hydrogen H 1 1s1 – 1s1

2 Lithium Li 3 1s2 2s1 [He]2s1 2s1

3 Sodium Na 11 1s2 2s2 2p63s1 [Ne]3s1 3s1

4 Potassium K 19 1s2 2s2 2p63s23p6 [Ar]4s1 4s1

5 Rubidium Rb 37 1s2 2s2 2p63s23p6 [Kr]5s1 5s1

6 Caesium Cs 55 1s2 2s2 2p63s23p6 [Xe]6s1 6s1

3d10 4s6 4p64p105s2

5d6 6s1

7 Francium Fr 87 1s2 2s2 2p63s23p6 [Rn]7s1 7s1

3d10 4s2 4p64d104f14

5s2 5p6 5d106s26p6

7s1

Electronic

configuration

with respect to

nearest noble

gases

Period

1 - - - - - -2 Beryllium Be 4 1s2 2s2 [He]2s2 2s2

3 Magnesium Mg 12 1s2 2s2 2p63s2 [Ne]3s2 3s2

4 Calcium Ca 20 1s2 2s2 2p63s23p6 [Ar]4s1 4s2

5 Strontium Sr 38 1s2 2s2 2p63s23p6 [Kr]5s2 5s2

3d104s24p65s2

6 Barium Ba 56 1s2 2s2 2p63s23p6 [Xe]6s1 6s1

3d10 4s6 4p64p105s2

5p6 6s2

7 Radium Ra 88 1s2 2s2 2p63p63d10 [Rn]7s1 7s2

4s2 4p6 4d104f145s2

5s6 5d10 6s26p67s2

Electronic con-

figuration

Valence shell

electronic

configuration

(ns1)

Element Symbol Atomic

Number

Electronic

configuration

with respect to

nearest noble

gases



40s- Block Elements


a) Among the alkali metals, sodium and potassium are abundant and lithium, rubidium and caesium

have lower abundance.

b) Sodium and potassium together make up over 4% by weight of the earth's crust. Sodium and

potassium are seventh and eighth most abundant elements respectively by weight in the earth's

crust.

c) Rubidium and caesium are obtained as a byproduct of lithium processing. They have lower

abundance.

d) Francium (223 Fr) being radioactive does not occur appreciably in nature because its half life

period is very small i.e. 21 minutes.

ii) Alkaline Earth Metals :

a) Beryllium is rare and found on surface deposits of beryl in pegmatite rocks.

b) Magnesium is the sixth most abundant element in the earth's crust and also occurs in the sea

water in the form of chlorides and sulphates upto the extent of 0.13%.

c) Calcium is fifth most abundant element in the earth's crust. It is found in vast sedimentary rocks

of CaCO3 existing as whole mountain ranges of limestone, marble and chalk.

d) Strontium and barium have much lower abundance.

e) Radium is the rarest of all comprising only 10–10 percent of igneous rocks. It occurs only in

association with uranium having terrestrial abundance of approximately 10–6 ppm.

Note:

Occurrence of s-block elements in lithosphere.

[ppm stands for parts per million. (1ppm 1g present in 106g sample)]

10.3 Anomalous properties of lithium

Q.9.Why does lithium show anomalous nature as compared to other members of group-l ?

Ans: i) Lithium, the first member of the group-l metals, shows anomalous behaviour as compared to the rest

of the members because of its

a) smallest size.

b) highest polarizing power (i.e., charge/radius ratio).

ii) Moreover, Lithium compounds are soluble in organic solvents as they have higher covalent character

than other alkali metals.

Note: Lithium shows diagonal relationship to magnesium.

Q.10. Discuss the differences between Lithium and other alkali metals.

Ans: The differences between Lithium and other alkali metals are as follows :

i) Physical properties: Lithium is much harder than other alkali metals and has higher melting and

boiling point.

ii) Reactivity :

a) Lithium is least reactive but strongest reducing agent amongst all alkali metals.

b) On combustion, lithium reacts with oxygen and nitrogen from air to form lithium monoxide

(Li2O) and lithium nitride (Li

3N) respectively. Other alkali metals cannot form such monoxide and

nitride compounds.

4Li + O2 2Li

2O

6Li + N2 2Li

3N

c) Lithium on reaction with ammonia forms lithium imide (Li2NH). Other alkali metals on reaction

with ammonia form corresponding amides of the general formula MNH2.

Li Na K Rb Cs Fr

18 ppm 2.27% by 1.84% by 78–12 ppm 2–6 ppm 10–18 ppm

Be Mg Ca Sr Ba Ra

2ppm 2.76% by 4.6% by 384 ppm 390 ppm 10–10 % by

weight weight weight



41s- Block Elements


Catalyst

3 2 22M 2NH 2MNH HAlkali Metal amidewhere M= Na,K,Rb,Cs

eg.

2Na + 2NH3 3 3Fe( NO ) 2NaNH

2 + H

2

Sodium Sodium

metal amide

iii) Compounds of Lithium :

a) Chloride of lithium (LiCl) is deliquescent and crystallizes as a hydrate (LiCl.2H2O) whereas

chlorides of other alkali metals do not form hydrates.

b) Lithium hydride is the most stable of all the alkali metal hydrides.

c) Lithium hydroxide is a weak base while hydroxides of other alkali metals behave as strong bases.

d) Lithium nitrate on heating decomposes to lithium monoxide (Li2O) whereas other alkali metal

nitrates decompose to give the corresponding nitrites.

4LiNO3 2Li

2O + 4NO

2 + O

2

Lithium Lithium

nitrate monoxide

2NaNO3 2NaNO

2 + O

2

Sodium Sodium

nitrate nitrite

e) Carbonate, fluoride and phosphate of lithium are sparingly soluble in water while that of the other

alkali metals are soluble in water.

f) Lithium hydrogen carbonate is not obtained in the solid form while other alkali metals form

corresponding solid hydrogen carbonates.

g) Lithium carbonate on heating undergoes decomposition to evolve CO2, whereas other alkali metal

carbonates do not.

Li2CO3 Li

2O + CO

2Lithium Lithium

carbonate monoxide

Note:

Deliquescent means property of a substance that inclines the substance to absorb moisture from the atmosphere

until it dissolves.

Q.11. Why is LiCI soluble in organic solvents? Explain.

Ans: Li+ has very high polarizing power (i.e., charge/radius ratio) and therefore, LiCI is covalent in nature. The

increased covalent character of lithium chloride is responsible for its solubility in organic solvents.

10.4 : Diagonal relationship between lithium and magnesium

Q.12. Explain the diagonal relationship between lithium and magnesium.

Ans: i) The similarities between an element of a group and the element placed in the next period of the

succeeding group is called diagonal relationship.

ii) Li and Mg show similarities in many of their properties (physical and chemical).

Group

Period 2

Period 3

1

Li

Na

2

Be

Mg

13

B

A1

14

C

Si

iii) Similarity in ionic sizes and polarizing power (charge/radius ratio) of the elements leads to formation of

diagonal relationship between them.



42s- Block Elements


iv) In case of lithium and magnesium, it is because

a) of their similar size

Atomic radii : Li = 152 pm, Mg = 160 pm

Ionic radii : Li+ = 76 pm, Mg++ = 72 pm

b) Atomic radii and polarizing power ofLi+ and Mg++ are nearly the same.

c) They have nearly similar electronegativities : Li (1.00) and Mg (1.20)

Q.13. In what respect lithium resembles magnesium? (NCERT)

Ans: Both lithium and magnesium show similarities in various physical and chemical properties as follows:

i) Hardness :

Both Li and Mg are harder than other elements in their respective groups.

ii) Solubility of chlorides :

Chlorides of lithium (LiCI) and magnesium (MgCl2) are deliquescent and also soluble in ethanol. These

chlorides form corresponding hydrates (LiCl.2H2O and MgCl

2.8H

2O) on crystallization from their

aqueous solutions.

iii) Reaction with oxygen :

Lithium and magnesium on reaction with oxygen form corresponding monoxides (viz.Li2O and MgO).

However, these oxides do not form super oxide on further reaction with excess of oxygen.

eg. 1) 4Li + O2 2Li

2O

Lithium Lithium

metal monoxide

2) Mg + O2 2MgO

Magnesium Magnesium

metal monoxide

(oxide)

iv) Basicity of hydroxides :

Hydroxides of lithium and magnesium are weak bases.

eg. 1) 2LiOH 2Li2O + H

2O

Lithium Lithium

hydroxide monoxide

2) Mg(OH)2 + O

2 MgO + H

2O

Magnesium Magnesium

hydroxide oxide

v) Reaction with nitrogen :

Both lithiumand magnesiumform correspondingnitrides (viz.,Li3 N and Mg

3N

2) on reaction with nitrogen.

eg. 1) 6Li + N2 2Li

3N

Lithium Lithium

nitride

2) 3Mg + N2 Mg

3N

2

Magnesium Magnesium

nitride

vi) Decomposition of carbonates :

Heating of lithium carbonate or magnesium carbonate results in their easy decomposition to form

corresponding oxides and carbon dioxide (CO2), Also, both lithium and magnesium cannot form solid

hydrogen carbonate.

vii) Reaction with water :

Both lithium and magnesium decompose water to form corresponding hydroxides and hydrogen.

However, heating is very much required for the reaction to take place.

eg. Mg + 2H2O Mg(OH)

2 + H

2

Magnesium Magnesium

hydroxide



43s- Block Elements


10.5 Periodic trends of alkali clements (metals) (Group-1 elements)

Q.14. Explain the following:

i) Alkali metals are never found in free state in nature. (NCERT)

Ans: a) All alkali metals are most electropositive metals. They have one valence electron (i.e., ns1) outside

the noble gas core.

b) This valence electron is loosely held and can be lost easily to produce corresponding monovalent

M+ ions. Hence, alkali metals show +1 oxidation state.

c) The monovalent M+ ions readily combine with other elements to form various compounds.

d) Thus, owing to their highly reactive nature, alkali metals are never found in free state.

ii) The trends in atomic and ionic radii as we move from Li to Cs.

Ans: a) The alkali metals have the largest atomic radii in their respective periods.

b) In the group, as atomic number increases, the valence electron enters a new shell and hence

atomic radii increases from top to bottom i.e. from Li to Cs.

c) Thus; atomic radii increases in the order of : Li < Na < K < Rb < Cs < Fr

d) The monovalent (M +) ions are smaller than the parent atoms.

eg.

iii) Alkali metals have low ionization energy.

Ans: a) As we move down the group from Li to Cs, there is an increase in atomic number, increase in

size, increase of nuclear charge and also increase in screening effect (i.e., the outermost electron

is very well screened from the nuclear charge).

b) Thus, alkali metals have low ionization energy and it decreases as we move down the group.

eg.

iv) Alkali elements are strong reducing agents.

Ans: Alkali metals have low value of ionization energy which decreases down the group. They can easily

lose their valence electrons and thus act as good reducing agents.

Note:

Alkali metal Atomic / metallic radius ionic radius of monovalent (M+)ion

Lithium Li = 152 pm Li+ = 76 pm

Sodium Na = 186 pm Na+ = 102 pm

Alkali metal Ionization enthalpy in kJ mol–1

Lithium 520

Cesium 376

Properties Lithium Sodium Potassium Rubidium Caesium Francium

Li Na K Rb Cs Fr

Atomic number 3 11 19 37 55 87

Atomic mass (g mool–1) 6.94 22.99 39.10 85.47 132.91 (223)

Electronic configuration [He]2s1 [Ne]3s1 [Ar]4s1 [Kr]5s1 [Xe]6s1 [Rn]7s1

Ionization enthalpy 520 496 419 403 376 ~375

(kJ mol–1)

Hydration enthalpy – 506 – 406 – 330 – 310 – 276 –

(kJ mol–1)

Metallic radius (pm) 152 186 227 248 265 –

Ionic radius M+(pm) 76 102 138 152 167 (180)

Melting point (K) 454 371 336 312 302 –

Boiling point (K) 1615 1156 1032 961 944 –

Density (g cm–3) 0.53 0.97 0.86 1.53 1.90 –

Standard potentials E/V – 3.04 – 2.714 – 2.925 – 2.930 – 2.927 –

for (M+ / M)



44s- Block Elements


10.6 Chemical reactivity of alkali metals

Q.15. Explain why alkali metals are very reactive.

Ans. i) Alkali metals have the largest atomic radii in their respective periods.

ii) Due to their large atomic size, they have low ionization enthalpy and form monovalent positive ions

(M+) very easily by the loss of one valence electron.

Therefore, alkali metals are very reactive.

Note:

The chemical reactivity of alkali metals increases down the group.

Q.16. What happens when alkali metals react with oxygen?

Ans: i) Action of air : In dry air, alkali metals react with oxygen to form corresponding oxides. This reaction

tarnishes the alkali metals. When these oxides react with moisture, they form corresponding hydroxides.

Action of oxygen: Alkali metals burn vigorously in oxygen forming. their corresponding oxides

(monoxide, peroxide or superoxides). However, oxidation state of alkali metal in all these oxides is +1.

On reaction with oxygen, lithium (Li) and sodium (Na) form corresponding monoxide and peroxide

whereas alkali metals like K, Rb and Cs form corresponding superoxides.

eg.

1) 4Li + O2 2Li

2O

Lithium Lithium

metal monoxide

2) 2Na + O2 Na

2O

2

Sodium Sodium

metal peroxide

3) M + O2 MO

2

Alkali Superoxide of

metal alkali metal

(Where M = K, Rb, Cs)

iii) Lithium and sodium cannot form superoxides as the presence of large cations (like K+, Rb+ or Cs+) only

can stabilise the superoxide ion (O2–)

Q.17.Lithium is the only alkali metal to form a nitride directly. Explain. (NCERT)

Ans: i) Lithium (having smallest atomic size in group-1) exhibits anomalous nature in reacting directly with

nitrogen from air to form stable lithium nitride (Li3N) whereas nitrides of other alkali metals are not

stable.

ii) This is because, both lithium ion (Li+) and nitride ion 3N are relatively smaller in size which results

in formation of stable compound.

6Li + N2 2Li3N

Lithium Lithium

nitride

Q.18.What is the oxidation state of

i) Na in Na2O2 and (NCERT)

ii) K in KO2?

Ans: i) Oxidation state of Na in sodium peroxide (Na2O

2) :

Let x be the oxidation state of Na in Na2O

2.

The oxidation state of each oxygen atom in peroxide ion is –1; therefore, net charge on peroxide ion

2

2O is –2 i.e. 2

O O

– 1 – 1

2x + (–2) = 0 x = + 1

Oxidation state of Na in Na2O

2 is + 1.



45s- Block Elements


ii) Oxidation state of K in potassium dioxide/potassium superoxide (KO2):

Let x be the oxidation state of K in KO2

The oxidation state of each oxygen atom in superoxide ion is –1/2 or – 0.5; therefore, net charge on

superoxide ion

Oxidation state of K in KO2 is + 1.

Note: Oxidation state of alkali metal is always +1.1

Q.19. Explain why sodium metal is preserved under kerosene?

Ans: i) Sodium metal on reaction with oxygen from air forms corresponding oxide which in turn reacts with

moisture to form corresponding hydroxide. These reactions tarnish the surface of sodium metal.

ii) Reaction of sodium with water is violent with evolution of hydrogen gas. Also the density of sodium

metal is less (0.968 g cm–3 at.298 K) than that of water (1.000 g cm–3 at 298 K). Therefore, sodium

metal cannot be preserved under water.

2Na + 2H2O 2NaOH + H

2

iii) Sodium metal does not react with kerosene, hence it is preserved under kerosene.

Q.20. Give chemical reactivity of alkali metals with water.

Ans: i) Alkali metals react with water to form corresponding hydroxides and evolve hydrogen (dihydrogen).

2M + 2H2O 2M+ 20H– + H

2ii) Alkali metals react explosively with water (lithium is an exception). Chemical reactivity increases down

the group as the electropositive character of metal increases in the order Li < Na < K < Rb < Cs.

Q.21. Explain the anomalous reaction of lithium with water.

Ans: i) Except Lithium, other alkali metals react vigorously with water.

ii) Lithium has the mostnegative EO value (–3.04 V) and sodium has the least EO value (– 2.714 V)

amongst the alkali metals.

iii) However, reaction of lithium with water is less vigorous than that of sodium. Lithium due to its small

atomic size and very high polarizing energy exhibits this anomalous nature.

Note:

The EO value is a measure of the tendency of the species to be reduced.

Q.22. Explain the hydride formation of alkali metals.

OR

Explain the reaction of hydrogen with alkali metals.

Ans: i) Alkali metals react with dry hydrogen (H2)to form corresponding hydrides. The reaction takes place at

high temperature and the hydrides formed have high melting points.

eg. Lithium reacts with dry hydrogen to form lithium hydride and the reaction takes place at

1073K.

2Li + H2 – 2LiH

ii) As we move down the group, the reactivity of alkali metals towards hydrogen decreases in the order.

Li > Na > K > Rb > Cs.

iii) This is because, as we move down the group, the size of the metal cation increases which in turn

decreases the lattice energy of the corresponding hydrides. Thus, from LiH to CsH stability of hydrides

decreases.

iv) Lithium and sodium besides their simple hydrides also form complex hydrides like LiA1H4 and NaBH

4

These complex hydrides are widely used in organic chemistry as powerful reducing agents.

Q.23. Explain reactivity of halogens with alkali metals.

Ans: i) All the alkali metals react vigorously with halogens to form their respective ionic crystalline halides with

general formula

22M X 2M X

Alkali Halogen Alkalimetal halide(ionic andcrystalline)



46s- Block Elements


(where M = Li, Na, K, Rb, Cs and X = F, CI, Br, I)

ii) The reactivity of alkali metals towards a halogen increases from lithium to caesium due to increase in

atomic radii and decrease in ionisation potential.

iii) Li ion with very small ionic size has a tendency to distort electron cloud around the negative halide

ion with large ionic size. Thus, halides of lithium have slightly covalent nature.

Q.24. Why is lithium iodide most covalent in nature among alkali halides ?

Ans: i) Among the alkali metals, Li is the smallest cation. Also anion I– has very large size.

ii) Thus, electron cloud around I– ion is easily distorted by Li ion leading to polarisation of anion and

covalency. (This is in accordance with Fajan's rule).

iii) Also the difference in electronegativities of Li and Iis small.

Therefore, lithium iodide is most covalent in nature among alkali halides.

Q.25. LiF is ionic hi nature while all other halides of lithium are covalent in nature. Explain.

Ans: i) Li+ ion is the smallest cation among alkali metals. Also F– ion is very small compared to other halogen

anions.

ii) According to Fajan's rule, covalency is favoured in larger anions.

iii) Also, the difference in electronegativities between Li and F is large while in all other halides of lithium

it is small.

Therefore, LiF is ionic in nature while all other halides of lithium are covalent in nature.

Q.26. Why is LiF almost insoluble in water whereas LiCI is soluble not only in water but also in acetone?

(NCERT)

Ans: i) For a substance to dissolve in water, its hydration energy must be greater than its lattice energy.

ii) LiF has very high lattice energy (–1045 kJ mol –1) as both Li+ and F– have small size.

iii) Hydration energy of LiF is also high (–1034 kJ mol–1) but it is less than that of its lattice energy. Thus,

LiF is almost insoluble in water.

iv) Due to the large size of Cl– ion, hydration energy of LiCl is more than that of its lattice energy and

therefore it is soluble in water. Also LiCl has some covalent character due to polarization which makes

it readily soluble in non-polar solvents such as acetone.

Q.27.Why is Li2CO

3 decomposed at lower temperature whereas Na

2CO

3 at higher temperature? (NCERT)

Ans: i) Alkali metals being highly electropositive, their carbonates are quite stable.

ii) However, in lithium carbonate, there is strong polarising action due to small size of Li+3 ion and large

size of 2

3CO ion imparting more covalent character..

iii) Also the lattice energy of Li2CO3 is low and hence less heat is required for the decomposition of

Li2CO

3

eg. Li2CO

3 Li

2O + CO

2

Lithium Lithium

carbonate monoxide

iv) In Na2CO

3, there is less polarisation and more ionic character. This is because, size of Na+ ion is larger

than that of Li+ ion.

v) Also, the lattice energy of Na2CO

3 is more and hence it decomposes at higher temperature.

Q.28. Explain why alkali metals are prepared by electrolysis of their fused salts. (NCERT)

Ans: i) Alkali metals are strong reducing agents. Hence, they cannot be prepared by chemical methods.

ii) Electrolysis of aqueous salt solution cannot be used for the preparation of alkali metals, as during

electrolysis, H+ are discharged at cathode giving H2 gas instead of alkali metal ion. This is due to the

fact that the discharge potential ofW ions is lower than the metal cations.

iii) However, on electrolysis of molten fused salt, the metal cation present gets discharged at the cathode

(as H+ ions are absent).

Hence, alkali metals are prepared by electrolysis of their fused salts.

10.7 : Important compounds of sodium

Q.29.ame some of the industrially important compounds of sodium.



47s- Block Elements


Ans: Some of the industrially important compounds of sodium are :

Q.30.ExplaiiI Solvay process for manufacture of sodium carbonate.

Ans: Solvay process is also known as ammonia soda process and is used in the manufacture of sodium carbonate.

NaCl, milk of lime and ammonia are the raw materials used in this process.

Process :

i) Solution of brine (NaCl) is saturated with ammonia and then carbon dioxide gas is bubbled through it to

form ammonium hydrogen carbonate.

NH3 + H

2O + CO

2 NH

4HCO

3

(From brine Ammonium hydrogen

solution) carbonate

ii) Ammonium hydrogen carbonate reacts with sodium chloride and sodium hydrogen carbonate is

precipitated.

NaCl + NH4HCO

3 NaHCO

3 + NH4Cl

(From brine Ammonium hydrogen Sodium hydrogen

solution) carbonate carbonate (ppt.)

iii) The precipitate is then filtered and igmted to get sodium carbonate (Na2CO

3).

2NaHCO3 Na

2CO

3 + CO

2 + H

2O

Filtered precipitate of Sodium

sodium hydrogen carbonate

carbonate

iv) NH4Cl obtained in the above reaction, is treated with milk of lime to recover NH

3 and a valuable

byproduct CaCl2 is obtained.

2NH4Cl + Ca(OH)

2 CaCl

2+ 2H

2O + 2NH

3

Ammonium Calcium

chloride chloride

Q.31. Explain how ammonia is recovered in Solvay process. (NCERT)

Ans: Ammonium chloride (NH4Cl) is obtained during the Solvay process for the preparation of Na

2CO

3. When

NH4Cl is treated with milk of lime, ammonia is recovered. Calcium chloride is obtained as an important

byproduct.

2NH4Cl + Ca(OH)

2CaCl

2+ 2H

2O + 2NH

3

Ammonium Calcium

chloride chloride

Q.32.Why potassium carbonate cannot be prepared by Solvay process?

Ans: i) In Solvay process, when CO2 is bubbled through an ammoniated brine, sodium hydrogen carbonate

(NaHCO3) being sparingly soluble in water gets precipitated.

ii) However, this is not the case with potassium carbonate (K2CO

3). Being fairly soluble in water, K

2CO

3

does not get precipitated.

Thus, potassium carbonate (K2CO

3) cannot be prepared by the Solvay process.

Q.33. What is the action of heat on hydrated sodium carbonate?

Ans: i) Sodium carbonate crystallizes from water as a decahydrate, Na2CO

3.10H

2O. This is also called washing

soda.

ii) Washing soda is readily soluble in water.

iii) On heating upto 373 K, there is loss of water of crystallization (9 molecules of water) and corresponding

monohydrate is obtained.

Chemical Common Name Formulae

Sodium carbonate Washing soda Na2CO

3

Sodium hydroxide Caustic soda NaOH

Sodium chloride Common salt NaCl

Sodium hydrogen carbonate Baking soda NaHCO3



48s- Block Elements


Na2CO

3.10H

2O 373K Na2CO3. H2O + 9H2O

Decahydrate of Monohydrate of

sodium carbonate sodium

carbonate

iv) When heating is continued above 373 K, there is further loss of water and monohydrate becomes

completely anhydrous forming white powder called soda ash.

Na2CO

3.H

2O above 373K Na

2CO

3 + H

2O

Monohydrate of Soda ash

sodium (Anhydrous

white powder)

Q.34. What is the action of water on sodium carbonate?

Ans: Sodium carbonate is hydrolysed by water.

Na2CO

3+ 2H

2O H

2CO

3+ 2NaOH

Sodium Carbonic acid Sodium

(Weak acid) hydroxide

(Strong base)

The solution becomes alkaline as H2CO

3 is a weak acid and NaOH is a strong base.

Q.35. What happens when carbon dioxide is bubbled through aqueous solution of sodium carbonate?

Ans: When CO2 is passed through aqueous solution of sodium carbonate, sodium hydrogen carbonate is obtained

as a product.

Na2CO

3 + H

2O + CO

2 2 NaHCO

3

Sodium Sodium

carbonate hydrogen

carbonate

Q.36. Describe the importance of sodium carbonate. (NCERT)

Ans: Sodium carbonate is used in

i) the manufacture of glass, soap, borax and caustic soda.

ii) softening of hard water in laundry and cleaning.

iii) qualitative and quantitative analysis as an important reagent.

iv) paper, paints and textile industries.

Q.37.Describe the preparation of sodium hydroxide by Castner - Kellner cell

OR

Explain the electrolysis method for preparation of sodium hydroxide.

Ans: i) Sodium hydroxide is generally prepared commercially by the electrolysis of sodium chloride in

Castner-Kellner cell (mercury cathode cell).

ii) Castner – Kellner cell consists of anode made up of carbon (graphite rod) and mercury cathode. Brine

solution is used as an electrolyte.

iii) During electrolysis, the following reactions take place:

NaCl Na+ + Cl–

a) At cathode: Sodium ions get reduced to metallic sodium at cathode. Sodium metal then combines

with mercury to form amalgam (Na – Hg).

Na+ + e– Na

Na + Hg Na – Hg

b) At anode : Cl– ions are oxidized to form chlorine gas.

iv) The amalgam is then treated with water to give sodium hydroxide and hydrogen gas.

2Na – Hg + 2H2O 2NaOH + 2Hg + H

2

Sodium

hydroxide

Note :



49s- Block Elements


Now a days, steel coated with titanium is used as anode. This is because titanium is very resistant to

corrosion and it prevents the problem of pitting and forming CO2. This problem is faced much more when

graphite rods are used as anode. Another advantage of using titanium is that it lowers the electrical resistance.

Q.38. What are the physical properties of sodium hydroxide?

Ans: i) Sodium hydroxide is a white, translucent solid having melting point 591 K.

ii) It readily dissolves in water forming a strong alkaline solution. The solution of sodium hydroxide at the

surface reacts with carbon dioxide in the atmosphere to form sodium carbonate.

2NaOH + CO2 � �� Na

2CO

3 + H

2O

Sodium Sodium

hydroxide carbonate

Q.39. Describe the importance of Sodium hydroxide.

Ans: Sodium hydroxide is used in the

i) purification of bauxite.

ii) manufacture of soap, paper, artificial silk and a number of chemicals.

iii) refining of petrol.

iv) textile industries for mercerizing cotton fabrics.

v) preparation of pure fats and oils.

vi) laboratory as an important reagent.

Q.40. Explain how common salt or table salt (Sodium chloride) is prepared.

Ans: i) Crude sodium chloride is obtained mainly by evaporation of sea water. However, it is deliquescent and

contains impurities like CaSO4, CaCl

2, MgCl

2, etc.

ii) When HCI gas is passed through saturated solution of crude NaCl, pure NaCl gets precipitated due to

common ion effect.

Q.41. What happens when sodium chloride is heated with concentrated sulpburic acid and manganese

dioxide ?

Ans: When sodium chloride is heated with concentrated sulphuric acid and manganese dioxide, it gets oxidised

and chlorine gas is liberated.

Q.42. What are the uses of sodium chloride (common salt)?

Ans: Sodium chloride is used

i) as a common salt or table salt for domestic purposes.

ii) in the preparation of compounds like Na2O

2, NaOH, Na

2CO

3, etc.

iii) as a preservative for meat, fish, etc.

iv) in the salting process of soap and

v) in the freezing mixtures to lower down temperature of ice.

Q.43. How is baking soda (sodium hydrogen carbonate) obtained from sodium carbonate?

Ans: When a solution of sodium carbonate is made saturated with carbon dioxide, sodium hydrogen carbonate is

formed which being less soluble in the solution gets separated out in the form of white crystalline powder.

Na2CO

3+ H

2O + CO

2 2NaHCO

3

Sodium Sodium hydrogen carbonate

carbonate (Baking soda)

Q.44.What happens when sodium hydrogen carbonate is heated ?

Ans: Sodium hydrogen carbonate on heating forms sodium carbonate, liberating carbon dioxide.

2NaHCO3 373K Na

2CO

3 + CO

2 + H2O

Sodium hydrogen Sodium

carbonate carbonate



50s- Block Elements


Q.45.Why is aqueous solution of NaHCO3 alkaline?

Ans: When dissolved in water, sodium hydrogen carbonate undergoes hydrolysis forming an alkaline solution:

NaHCO3 + H

2O NaOH + H

2CO

3

Sodium Sodium Carbonic acid

hydrogen hydroxide (Weak acid)

carbonate (Strong base)

Presence of strong base i.e., NaOH makes the solution alkaline.

Q.46. What are the uses of sodium hydrogen carbonate?

Ans: Sodium hydrogen carbonate (NaHCO3) is used

i) in fire extinguisher.

ii) as a constituent of baking powder which is a mixture of starch, sodium hydrogen carbonate and

potassium hydrogen tartrate.

iii) in medicines as an antacid (which minimizes the acidity of stomach).

iv) in the baking of cakes, breads, etc. (when dough of cakelbread is heated, NaHCO3 decomposes

evolving CO2 which makes cake/bread porous).

10.8 Uses of alkali metals

Q.47. Explain the uses offollowing alkali metals.

i) Lithium ii) Sodium iii) Potassium iv) Caesium

Ans: i) Lithium

a) Lithium is used in manufacture of some important alloys.

b) Lithium is used for producing thermonuclear energy, which is required for propelling rockets and

guided missiles.

c) Lithium hydroxide (LiOH) is used in removing CO2 from exhaled air in submarines and space

vehicles.

d) Lithium bromide (LiBr) is used in medicines as a sedative.

e) Lithium chloride (LiCl) is used in air conditioning plants to regulate humidity.

ii) Sodium :

a) Sodium is used to prepare Na/Pb alloy. This alloy is used in preparing antiknocking additives like

PbEt4 and PbMe

4 in petrol.

b) Liquid sodium metal is used as a coolant in fast breeder nuclear reactors.

c) Sodium metal is used as a reducing agent in the extraction of boron (B) and silicon (Si).

d) Sodium is also used as an important reagent in the Wurtz reaction.

e) It is used in the manufacture of sodium vapour lamp.

iii) Potassium :

a) Potassium has a vital role in biological system.

b) Potassium chloride (KCI) is used as a fertilizer.

c) Potassium hydroxide (KOH) is used in the manufacture of soft soaps and also as an excellent

absorbent of carbon dioxide.

d) In submarine, space shuttles and in emergency breathing apparatus, potassium superoxide (KO2)

is used as a source of oxygen.

1) When potassium superoxide comes in contact with moisture (from breath) it liberates oxygen

and potassium hydroxide.

4KO2

+ 2H2O 4KOH + 3O

2

Potassium (Moisture Potassium Oxygen

superoxide from hydroxide

breath) carbonate

Alloy % of lithium in the alloy Used for

Li – Pb 0.05% Making toughened bearings.

Li – Al 2.45 % Construction of aircrafts.

Li – Mg 14 % Making armour plates and components of aerospace



51s- Block Elements


iv) Caesium :

Caesium is used in devising photoelectric cells.

10.9 Biological importance of sodium and potassium

Q.48.Explain the importance of sodium and potassium in biological system. (NCERT)

Ans: i) Sodium and potassium playa vital role in biological systems as they are highly mobile unipositive

cations and form large number of soluble salts. They are strongly solvated in water,

ii) Both Na+ and K+ions control muscle contraction and relaxation by maintaining sensitivity of nerves

and are thereby required for smooth functioning of muscles and nervous system.

eg. Na+ ions depress the activity of muscle enzyme and are required for muscle contraction. K+ ions

permit the heart muscles to relax between the beats.

iii) Both Na+ and K+ are required,

a) for maintaining constant osmotic pressure on either side of the cell wall.

b) to regulate the acid-base balance of body fluids.

c) as structure promoters for proteins and polynucleic acids (DNA and RNA).

iv) K+ is especially required as an enzyme activator. In the form of compounds, they help in various

activities.

eg.

a) Acid-base balance of body fluid is generally maintained by using sodium carbonate as buffer. It

also helps in transportation of CO2

b) Sodium chloride (NaCl) acts as a source of hydrochloric acid (HCl) for gastric juices.

Q.49. Mention the sources of sodium and potassium in biological system.

Ans: i) Human bodies obtain sodium and potassium from plants i.e., from fruits and vegetables.

ii) Coffee, tea, cocoa, dried beans molasses, green leafy vegetables, milk, fish, bananas, oranges, pineapples,

potatoes,.etc are the important sources for potassium.

iii) In diet, the most important source of sodium is common salt.

Note:

1) A typical 70 kg man contains about 90 g of Na and 170 g of K compared to only 5 g of iron and 0.06

g of copper.

2) Daily requirement of NaC1 is minimum 5 –

10 and that of KCl is 4g approximately.

Q.50. Write a short note on concentration of Na+

and K+ ions in vertebrates.

Ans: i) In vertebrates,

a) cytoplasm (inside the cell) and tissues

contain high concentration of potassium

(K+) ion and low concentration of

sodium (Na+) ion.

eg. Red blood cells (RBC's) contain

105mg L–1 of potassium (K+) ions and

only 10mg L–1 of sodium (Na+) ions.

b) While in the blood plasma (outside the cell), there is higher concentration of sodium ion (Na+)

and low concentration of potassium ion (K).

eg. Blood plasma contains 143 mg L–1 of sodium (Na+) ions and only 5 mg L–1 of potassium

(K+) ions. There is a development of potential difference across the cell membrane due to

difference in the concentrations of Na+ and K+ inside and outside of the cell. This potential

difference allows the nerve fibres to conduct impulses and the muscles to contract.

Q.51. What are the ill-effects of deficiency of sodium and potassium in biological system.



52s- Block Elements


Ans: i) Deficiency of sodium in human body causes

a) reduction in fat deposit.

b) atrophy of muscle and testis.

c) lung infection.

d) retarded bone growth and reduction in osteoid tissue.

e) low blood pressure and

f) circulatory failure.

ii) Deficiency of potassium causes

a) reduction in heart beats.

b) scarring of heart muscle.

c) hypertrophy of kidneys and

d) paralysis of muscles.

Q.52. Explain why Sodium is found to be more useful than potassium. (NCERT)

Ans: i) Sodium ions are primarily found in blood plasma and interstitial fluid which surrounds the cell while

potassium ions are present within the cell fluids.

ii) Sodium ions perform the following important functions.

a) Transmission of nerve signals.

b) Regulating the flow of water across cell membranes.

c) Transport of sugars and amino acids inside the cell.

iii) Besides its biological importance, sodium has many other applications.

a) In the extraction of Band Si, metallic sodium is used as a reducing agent.

b) Sodium is an important reagent for qualitative analysis of organic compounds and for carrying out

Wurtz synthesis.

c) Liquid sodium is used as a coolant.

iv) Also, Sodium is more abundant than potassium and is proved to be more useful than potassium.

10.10 Periodic trends of alkaline earth metals (Group-2 elements]

Q.53. Why are the elements of group-2 called alkaline earth metals?

Ans: i) Beryllium (Z = 4), Magnesium (Z = 12), Calcium (Z = 20), Strontium (Z = 38), Barium

(Z = 56) and Radium (Z = 88) together constitute group-2.

ii) These elements (except beryllium) form alkaline hydroxides and alkaline metal oxides, which are found

in earth's crust.

Hence, elements of group-2 are called as 'alkaline earth metals'.

Q.54. Alkaline earth metals show +2 oxidation state. Explain.

Ans: i) General electronic configuration of alkaline earth metals can be represented as [noble gas] ns2 Thus,

there are two electrons in s-orbital of the valence shell.

ii) By losing these two valence electrons, alkaline earth metals can acquire stable noble gas configuration.

Thus, they form stable divalent cation (M+2) and exhibit +2 oxidation state in their ionic compounds,

Q.55. Discuss the trends in atomic and ionic radii of alkaline earth metals. .

Ans: i) As we move across the period from alkali metals to alkaline earth metals, atomic and ionic radii

decreases due to the increase in atomic number as well as nuclear charge.

ii) As we move down the group from Be to Ba, the valence electron enters a new shell hence, the atomic

and ionic radii increases with the increase in atomic number.

Q.56. Discuss the trends in ionization enthalpies of alkaline earth metals.

Ans: i) Alkaline earth metals have large atomic size and their ionization enthalpies (energies) are low.

ii) As we move down the group from Be to Ba, their atomic size increases and ionization enthalpy

decreases.

Q.57. Distinguish between alkali metals and alkaline earth metals.



53s- Block Elements


Ans:

Q.58.Compare the alkali metals with alkaline earth metals with respect to

i) ionization enthalpy ii) basicity of oxides

iii) solubility of hydroxides.

Ans: Comparison between alkali metals and alkaline earth metals.

Note:

Atomic and physical properties of the alkaline earth metals are as follows:

Properties Alkali metals Alkaline earth metals

i. General electronic configuration ns1 ns2

ii. Electrons in valence shell one two

iii. Oxidation state + 1 + 2

iv. Nature Soft Hard

v. Reactivity Highly reactive Less reactive

vi. Oxide formation form strong basic oxides form weak basic oxides and

and hydroxides hydroxides

vii. Solubility of corresponding soluble in water sparingly soluble in water.

a. carbonates

b. sulphates, phosphates and soluble in water insoluble in water

Properties Alkali metals Alkaline earth metals

Ionization enthalpies i. Ionization enthlpies of alkali i) Atomic size of alkaline earth metals

metals are low as the outermost is smaller than corresponding alkali

electron is very well screened metals. Thus, the first ionization

from the nuclear charge enthalpies of alkaline earth metals are

higher than that of corresponding alkali

metals

ii. As we move down the group ii. As we move down the group from Be

from Li to Cs, the ionization to Ba, the value of first ionization

enthalpies decreases due to the enthalpy decreases due to increase in

increase in atomic size, atomic the atomic size. However, the second

number, screening effect and ionization enthalpies of alkaline earth

nuclear charge. metals are smaller than those of

corresponding alkali metals.

Basicity of oxides Very highly basic (when Moderately basic

dissolved in water give highly

basic solution).

Solubility of Highly soluble in water.They Less soluble in water. They undergo

hydroxides undergo exothermic dissolution exothermic dissolution in H2O to

in H2O. lesser extent as compared to alkali

metal.



54s- Block Elements


10.11 Chemical reactivity

Q.59. Explain the trends in chemical reactivity and the nature of bonds in alkaline earth metals.Ans: i) Trends in chemical reactivity :

a) Alkaline earth metals owing to their low ionization energy are fairly reactive. However, theirchemical reactivity is lower than corresponding alkali metals.

b) As we move down the group from Be to Ba, atomic number and electropositive character increasesand thus, there is an increase in the chemical reactivity.

ii) Nature of bond :a) Beryllium mostly forms covalent compounds because of its small size, high electronegativity and

high enthalpy.b) Compounds of magnesium show partly ionic and partly covalent character. Ca, Sr and Ba form

compounds of purely ionic character.Q.60. Explain the reaction of alkaline earth metals with oxygen.Ans: i) When heated with oxygen, beryllium and magnesium form oxide film on their surface as both Be and

Mg are kinetically inert to the reaction with oxygen.However, powdered beryllium bums brilliantly on ignition in air to produce beryllium oxide (BeO) andberyllium nitride (Be

3N

2).

2Be + O2 2BeO

Powdered From Berylliumberyllium air oxide

Be + N2 Be

3N

2

Powdered From Berylliumberyllium air nitride

ii) Magnesium being more electropositive than beryllium bums with dazzling brilliance in air to givemagnesium oxide (MgO) and magnesium nitride (Mg

3N

2).

2Mg + O2

2MgO

From Magnesiumair oxide

3Mg + N2

Mg3N

2

From Magnesiumair nitride

iii) When heated with oxygen, barium (Ba), strontium (Sr) and radium (Ra) form corresponding peroxides.

2M + O2 2MO (M = Be, Mg or Ca)

Properties Beryllium Magnesium Calcium Strontium Barium Radium

Li Na K Rb Cs Fr

Atomic number 4 12 20 38 56 88

Atomic mass (g mol–1) 9.01 24.31 40.08 87.62 137.33 226.03

Electronic [He] 2S2 [Ne]3s2 [Ar] 4s2 [Kr] 5s2 [Xe] 6s2 [Rn] 7s2

configuration

Ionization enthalpy (I)

(kJ mol–1) 899 737 590 549 503 509

Ionization enthalpy

(II) (kJ mol–1) 1757 1450 1145 1064 965 979

Hydration enthalpy

(kJ mol–1) – 2494 –1921 –1577 –1443 –1305 –

Metallic radius (pm) 111 160 197 215 222 –

Ionic radius M2+(pm) 31 72 100 118 135 148

Melting point (K) 1560 924 1124 1062 1002 973

Boiling point (K) 2745 1363 1767 1655 2078 (1973)

Density (g cm–3) 1.84 174 1.55 2.63 3.59 (5.5)

Standard potentials EO

for (M2+/M) (V) –1.97 –2.36 –2.84 –2.89 –2.92 –2.92



55s- Block Elements


Alkaline Pure Metalearth metal oxygen oxide

M + O2 MO

2 (M = Ba, Sr or Ra)

Alkaline Pure Metalearth metal oxygen peroxideThe affinity of metals towards oxygen increases down the group.

Q.61. Explain the reactivity of alkaline earth metals towardsi) Water ii) Hydrogen iii) Halogens

Ans: i) Reaction with water :a) Alkaline earth metals react with water to evolve hydrogen gas.

M + 2H2O M(OH)

2 + H

2 (where M = Mg, Ca, Sr or Ba)

Alkaline water Metal hydrogenearth hydroxide gasmetals

b) As we move down the group, the chemical reactivity of alkaline earth metal increases in the orderMg < Ca < Sr < Ba.

c) Be does not react even with boiling water, Mg reacts with boiling water while Ca, Sr, Ba reactvigorously even with cold water.

ii) Reaction with hydrogen :All alkaline earth metals except Be, on heating with hydrogen combine directly to form correspondingmetal hydrides of the general formula, MH2.M + H

2 MH

2(where M = Mg, Ca, Sr or Ba)

Alkaline Metalearth hydridemetals

iii) Reaction with halogens :All alkaline earth metals combine with halogen to form their corresponding halides. The reaction takesplace at high temperature.M + X

2 MX

2(M = Be, Mg, Ca, Sr, Ba, Ra and X = F, CI, Br, I)

Alkaline Metalearth halidemetaleg.Ca + Cl

2 CaCl

2

Calcium Calciumchloride

Q.62. How are the following compounds prepared ?i) BeH

2ii) BeF

2iii) BeCl

2

Ans: i) Preparation of BeH2 : Beryllium hydride (BeH

2) is obtained by reduction of beryllium chloride (BeCl

2)

with lithium aluminium hydride (LiAlH4).

2BeCl2

+ LiAlH4 2BeH

2+ LiCl + AlCl

3

Beryllium Lithium Beryllium Lithium Aluminiumchloride aluminium hydride chloride chloride

hydrideii) Preparation of BeF

2: Beryllium fluoride (BeF

2) is prepared by thermal decomposition of ammonium

fluoroberyllate, [(NH4)

2BeF

4] in presence of carbon dioxide (CO

2).

(NH4)

2BeF

4

2CO

2NH4F + BeF

2

Ammonium Berylliumfluoroberyllate fluoride

Note : This is one of the best method for preparation of BeF2

iii) Preparation of BeCl2 : Beryllium chloride (BeCl

2) is prepared from beryllium oxide (BeO) and carbon

in the current of chlorine between 600 K to 800 K.

BeO + C + Cl2

600 800 K� � � � � ��

BeCl2 + COBeryllium Beryllium oxide chloride

Q.63.What is hydrolith?Ans: Calcium hydride, CaH

2 is known as hydrolith.

Q.64.Classify the following hydrides of alkaline earth metals as covalent, ionic or partly ionic.



56s- Block Elements


BeH2, BaH

2, CaH

2, MgH

2' SrH

2

Ans:

2 2 2 2 2

Covalent hydride Partly ionic hydride Ionic hydride

BeH MgH CaH ,SrH ,BaH

Q.65. What happens when hydrides of alkaline earth metals react with water?Ans: Hydrides of alkaline earth metals on reaction with water behave as strong reducing agents and form

corresponding metal hydroxides along with evolution of hydrogen gas.MH

2+ 2H

2O M(OH)

2 + 2H

2Hydride of Metalalkaline earth hydroxidemetal

10.12 Anomalous properties of beryllium

Q.66. Why does beryllium show anomalous nature as compared to the rest of the members of the group-2?Ans: Beryllium, the first member of the group-2 metals, shows anomalous behaviour as compared to the rest of

the members of the group-2 because of itsi) smaller atomic and ionic radii andii) higher electronegativity.

Q.67.Discuss the differences between beryllium and other members of group-2.i) Be is a hard metal while other alkaline earth metals are soft.ii) Be is the least metallic element as compared to other alkaline earth metals.iii) As beryllium has high ionization enthalpy and small size, it forms compounds which are largely covalent

and it also gets hydrolysed easily.iv) Beryllium has the highest melting point, boiling point and ionization enthalpy compared to all other

alkaline earth metals.v) BeO and Be(OH)

2 are amphoteric in nature while oxides and hydroxides of other alkaline earth metals

are basic in nature.vi) Be does not liberate H

2from acids (HCl, H

2SO

4),while other metals do.

vii) Beryllium does not show coordination number more than four, as in its valence shell there are only fourorbitals (2s and 2p). The remaining members of the group can have a coordination number of six bymaking use of d-orbitals.

10.13 Uses of alkaline earth metals

Q.68. Write important uses of alkaline earth metals.Ans: i) Important uses of beryllium :

a) Beryllium is used in the manufacture of alloys.eg. High strength springs are prepared using copper-beryllium (Cu–Be) alloy.

b) Metallic beryllium is used for making windows of X-rays tubes.ii) Important uses of magnesium :

a) As magnesium is a light metal, its alloys with aluminium and zinc are used in aircraft construction.eg. Elelctron(95% Mg + 5% Zn) and Magnalium (1 – 15%Mg + 85 - 99% A1) are used inconstruction of aircrafts.Magnalium is also used in the construction of light instruments. .

b) In medicine, magnesium hydroxide [Mg(OH)2]in its suspension form is used as an antacid.

c) In toothpaste, one of the ingredients used is magnesium carbonate (MgCO3).

iii) Important uses of calcium :a) Calcium is used to remove

1) air from vacuum tubes owing to its reactivity with oxygen and nitrogen at elevatedtemperatures.

2) sulphur from petroleum3) last traces of water from alcohol.

b) Extraction of some metal oxides using carbon is ineffective, therefore, in such situations calciumis used as reducing agent.

c) Compounds of calcium such as limestone and gypsum are used as constituents of cement and mortar.iv) Important uses of barium :

a) BaSO4 being insoluble in H

2O and opaque to X-rays is used as 'barium meal' to scan the X-ray of human

digestive system.b) Barium reacts with oxygen and nitrogen at high temperature, hence, it is used to remove air from vacuum

tubes.





58s- Block Elements


10.14 : Diagonal relationship between beryllium and aluminium

Q.69. How does beryllium resemble aluminium with respect to ionic radii ?

Ans: i) Beryllium is the first member of group-2 metals whereas aluminium is the second member of the

group-13 elements. The ionic radius of Be2+ is 31 pm and that of Al3+ is 53.5 pm.

ii) But the charge/radius ratio is nearly the same for Be2+ and Al3+ ion (i.e., charge to radius ratio of Be is

0.064 while that of Al is 0.060).

Hence, beryllium resembles aluminium with respect to ionic radii.

Q.70. Write a note on the diagonal relationship between Be and A1.

OR

What are the similarities between beryllium and aluminium ?

Ans: i) Beryllium is placed in the group-2 and period-2 of the modem periodic table. It resembles aluminium

(which is placed in group-13 and period-3).

Due to nearly same charge to radius ratio, beryllium (0.064) and aluminium (0.060) exhibit diagonal

relationship.

Due to diagonal relationship and nearly same charge to radius ratio, beryllium (0.064) and aluminium

(0.060) show certain similarities. They are :

a) Both Be and Al have tendency to form covalent compounds.

b) There is a presence of oxide film on the surface of beryllium and aluminium. Hence, both these

metals cannot be readily attacked by acids.

c) Both Be and Al form complexes.

eg. 2

4BeF and 3

6AlF

d) The oxides (BeO and Al2O

3) and hydroxides [Be(OH)

2 and Al

2(OH)

3] of both beryllium and

aluminium are amphoteric in nature.

e) Hydroxides of both Be and Al dissolve in excess alkali to form beryllate ion [Be(OH)4]2– and

aluminate ion [A1(OH)4]–

f) Carbides of both, beryllium and aluminium hydrolyse to form methane.

Be2C + 4H

2O 2Be(OH)

2 + CH

4

Beryllium

carbide

Al4C

3+ 12H

2O 4Al(OH)

3 + 3CH

4

Aluminium Methane

carbide

g) Anhydrous BeCl2 and A1Cl

3 are incomplete octet molecules and act as Lewis acids. They are

soluble in organic solvents and used as catalysts in Friedel-Craft reaction.

10.15 : Important compounds of calcium

Q.71.How is quick lime prepared from limestone ?

Ans: Quick lime is prepared on commercial scale by heating limestone (CaCO3) in a reverberatory kiln at

1070 – 1270 K.

CaCO3 heat� � �� CaO + CO

2

Calcium Calcium

carbonate oxide

The reaction is made to proceed to completion by removing the carbon dioxide as soon as it is produced.

Q.72. Enlist the various physical properties of calcium oxide.

Period 2

Period 3

Group 1 2 3

Li

Na

Be

Mg

B

Al



59s- Block Elements


Ans: i) Calcium oxide is a white amorphous solid with a melting point of 2870 K.

ii) It absorbs moisture and carbon dioxide when it is exposed to atmosphere.

Q.73. What happens when

i) calcium oxide is exposed to atmosphere.

ii) calcium oxide is heated with ammonium chloride.

iii) calcium oxide is combined with P40.0,

Ans: i) Calcium oxide is exposed to atmosphere:

When calcium oxide is exposed to atmosphere, it absorbs moisture and carbon dioxide.

CaO + H2O Ca(OH)

2

Calcium Calcium

oxide hydroxide

CaO + CO2 CaCO

3

Calcium Calcium

oxide carbonate

ii) Calcium oxide is heated with ammonium chloride :

Calcium oxide (CaO) on heating with ammonium chloride (NH4Cl) forms ammonia

CaO + 2NH4Cl CaCl

2+ 2NH

3+ H

2O

Calcium Ammonium Calcium Ammonia

oxide chloride chloride

iii) Calcium oxide is combined with P4O

10 :

Quick lime, being basic, reacts with acidic phosphorus pentoxide at high temperatures to form calcium

phosphate.

6CaO + P4O10 2Ca

3(PO

4)

2

Calcium Phosphorus

oxide pentoxide

Q.74. Explain what is slaking of lime.

Ans: i) The addition of limited quantity of water breaks the lumps of lime forming slaked lime and the process

is called slaking of lime.

CaO + H2O Ca(OH)

2; H = – 63 kJ mol–1

Calcium slaked lime

oxide

ii) This reaction is exothermic and produces a hissing sound.

iii) The product formed Ca(OH)2 is called slaked lime.

Q.75. What i~ milk of lime?

Ans: The suspension of slaked lime [Ca(OH)2] in water is called milk of lime.

Q.76. What is sodalime?

Ans: Quick lime slaked with soda gives sodalime.


i) quick lime is heated with silica ?

ii) chlorine reacts with slaked lime ?

Ans: i) Quick lime is heated with silica :

Quick lime is a basic oxide, hence heated with silica, it gives calcium silicate.

CaO + SiO2 CaSiO

3

Calcium Silica Calcium silicate

oxide

(quick lime)

ii) Chlorine reacts with slaked lime:

When dry slaked lime is subjected to the action of chlorine, bleaching powder is formed.

Ca(OH)2 + Cl

2 CaOCl

2 + H

2O

Slaked lime Bleaching powder



60s- Block Elements


Q.78. Give the uses of calcium oxide.

Ans: Calcium oxide is used

i) in the manufacture of sodium carbonate from caustic soda (NaOH), dye stuff, etc.

ii) in large scale production of cement wherein it acts as an important primary material.

iii) in purification of sugar.

iv) as a cheapest form of alkali.

Q.79. How does calcium carbonate occur in nature?

Ans: Calcium carbonate (CaCO3) occurs in many forms like chalk, limestone, marble slate, calcite etc.

Q.80. Give the physical properties of calcium carbonate.

Ans: Physical properties of CaC03 :

i) It is white fluffy powder. ii) It is almost insoluble in water.

Q.81. Explain the various methods for preparation of calcium carbonate.

Ans: i) Calcium carbonate is prepared by passing carbon dioxide through slaked lime.

Ca(OH)2 + CO

2 CaCO

3 + H

2O

Slaked Calcium

lime carbonate

Note:

When excess of CO2 is present, it leads to the formation of water soluble calcium hydrogen carbonate.

CaCO3 + H

2O + CO

2 Ca(HCO

3)

(insoluble) (soluble)

Hence, while preparing calcium carbonate from slaked lime, controlled addition of CO2 is essential.

ii) Calcium carbonate can also be prepared by adding sodium carbonate to calcium chloride.

CaCl2 + Na

2CO

3 CaCO

3 + 2NaCl

Calcium Calcium

chloride carbonate


i) calcium carbonate is thermally decomposed?

ii) calcium carbonate reacts with dilute mineral acids?

Ans: i) When calcium carbonate is thermally decomposed it decomposes to calcium oxide along with

evolution of carbon dioxide.

CaCO3 1200 KCaO + CO

2

Calcium Calcium

carbonate oxide

ii) Calcium carbonate reacts with dilute mineral acids (HCI, H2SO

4, etc.) to liberate carbon dioxide.

CaCO3 + 2HCl

(dil) CaCl

2+ H

2O + CO

2

Calcium Calcium

carbonate chloride

CaCO3

+ H2SO

4(dil) CaSO4 + H

2O + CO

2

Calcium Calcium

carbonate sulphate

Q.83. Describe tile importance of limestone.

OR

Give the important uses of calcium carbonate.

Ans: i) Calcium carbonate is used in the manufacture of quick lime.

ii) It is also used as a building material in the form of marble.

iii) Mixture of CaCO3 and MgCO

3 is used as a flux in the extraction of iron metal.

iv) Specially precipitated calcium carbonate is extensively used in the manufacture of high quality paper.

v) It is a kind of antacid.

vi) It is used as a mild abrasive in toothpaste.

vii) It is one of the constituent of chewing gum.



61s- Block Elements


10.16 : Biological importance of magnesium and calcium

Q.84. Explain the role of Ca in biological system. (NCERT)

OR

What is the biological importance of calcium ?

Ans: i) An adult body contains about 1200 g of Ca compared with only 5 g of iron and 0.06 g of copper.

Maximum percentage (90%) of calcium is present in bones and teeth.

ii) The daily requirement of calcium in the human body has been estimated to be 200 – 300 mg of

calcium.

iii) Calcium plays important role in vital functions like neuromuscular function, interneuronal transmission,

cell membrane integrity and blood coagulation. The calcium concentration in plasma is regulated at

about 100 mg L–1

iv) Deficiency of calcium causes rickets, osteoporosis, osteomalacia.

Q.85. Explain the role of Mg in biological system. (NCERT)

OR

What is the biological importance of magnesium ?

Ans: i) An adult body contains about 25 g of Mg compared with only 5 g of iron and 0.06 g of copper.

ii) Magnesium is present in chlorophyll which is the main pigment for the absorption oflight in plants.

iii) All enzymes that utilize ATP in phosphate transfer, require magnesium as cofactor.

iv) Deficiency of magnesium results into convulsion and neuromuscular irritation.

Quick Review



62s- Block Elements




63s- Block Elements


Additional Theory Questions

1) Give reasons :

i) Group 1 elements are known as 'alkali metals'.

Ans: i) Hydrogen (Z = 1), Lithium (Z = 3), Sodium (Z = 11), Potassium (Z = 19), Rubidium (Z = 37),

Caesium (Z = 55) and Francium (Z = 87) together constitute group-I.

ii) Oxides and hydroxides of group-l elements on combining with water form water soluble bases

i.e., alkali. Hence, elements of group-I are called as 'alkali metals' .

eg. Na2O + H

2O 2NaOH

iii) The word 'alkali' is derived from arabic word 'alquis' meaning 'plant ashes' which are rich in the

carbonates of sodium and potassium.

ii) Group 2 elements are known as 'alkaline earth metals'.

Ans: i) Beryllium (Z = 4), Magnesium (Z = 12), Calcium (Z = 20), Strontium (Z = 38), Barium

(Z = 56) and Radium (Z = 88) together constitute group-2.

ii) These elements (except beryllium) form alkaline hydroxides and alkaline metal oxides, which are

found in earth's crust.

Hence, elements of group-2 are called as 'alkaline earth metals'.

2) Why lithium and magnesium show diagonal relationship between them ?

Ans: i) Similarity in ionic sizes and polarizing power (charge/radius ratio) of the elements leads to formation of

diagonal relationship between them.

ii) In case of lithium and magnesium, it is because

a) of their similar size

Atomic radii : Li = 152 pm, Mg = 160 pm

Ionic radii : Li+ = 76 pm, Mg++ = 72 pm

b) Atomic radii and polarizing power ofLi+ and Mg++ are nearly the same.

c) They have nearly similar electronegativities : Li (1.00) and Mg (1.20)

3) Explain significant similarities between physical and chemical properties ofl ithium and magnesium ?

Ans: Both lithium and magnesium show similarities in various physical and chemical properties as follows:

i) Hardness :

Both Li and Mg are harder than other elements in their respective groups.

ii) Solubility of chlorides :

Chlorides of lithium (LiCI) and magnesium (MgCl2) are deliquescent and also soluble in ethanol. These

chlorides form corresponding hydrates (LiCl.2H2O and MgCl

2.8H

2O) on crystallization from their

aqueous solutions.

iii) Reaction with oxygen :

Lithium and magnesium on reaction with oxygen form corresponding monoxides (viz.Li2O and MgO).

However, these oxides do not form super oxide on further reaction with excess of oxygen.

eg. 1) 4Li + O2 2Li

2O

Lithium Lithium

metal monoxide

2) Mg + O2 2MgO

Magnesium Magnesium

metal monoxide

(oxide)

iv) Basicity of hydroxides :

Hydroxides of lithium and magnesium are weak bases.

eg. 1) 2LiOH 2Li2O + H

2O

Lithium Lithium

hydroxide monoxide

2) Mg(OH)2 + O

2 MgO + H

2O

Magnesium Magnesium



64s- Block Elements


hydroxide oxide

v) Reaction with nitrogen :

Both lithiumand magnesiumform correspondingnitrides (viz.,Li3 N and Mg

3N

2) on reaction with nitrogen.

eg. 1) 6Li + N2 2Li

3N

Lithium Lithium

nitride

2) 3Mg + N2 Mg

3N

2

Magnesium Magnesium

nitride

vi) Decomposition of carbonates :

Heating of lithium carbonate or magnesium carbonate results in their easy decomposition to form

corresponding oxides and carbon dioxide (CO2), Also, both lithium and magnesium cannot form solid

hydrogen carbonate.

vii) Reaction with water :

Both lithium and magnesium decompose water to form corresponding hydroxides and hydrogen.

However, heating is very much required for the reaction to take place.

eg. Mg + 2H2O Mg(OH)

2 + H

2

Magnesium Magnesium

hydroxide

4) Alkali metals show + 1 oxidation state.

Ans: a) All alkali metals are most electropositive metals. They have one valence electron (i.e., ns1) outside the

noble gas core.

b) This valence electron is loosely held and can be lost easily to produce corresponding monovalent M+

ions. Hence, alkali metals show +1 oxidation state.

5) What happens when sodium hydroxide reacts with CO2? Refer Q.38.ii.

Ans: i) It readily dissolves in water forming a strong alkaline solution. The solution of sodium hydroxide at the

surface reacts with carbon dioxide in the atmosphere to form sodium carbonate.

2NaOH + CO2 � �� Na

2CO

3 + H

2O

Sodium Sodium

hydroxide carbonate

6. What happens when magnesium is burnt in air ?

Ans: i) Magnesium being more electropositive than beryllium bums with dazzling brilliance in air to give

magnesium oxide (MgO) and magnesium nitride (Mg3N

2).

2Mg + O2

2MgO

From Magnesium

air oxide

3Mg + N2

Mg3N

2

From Magnesium

air nitride

7) Write the important uses of :

i) Important uses of beryllium :

a) Beryllium is used in the manufacture of alloys.

eg. High strength springs are prepared using copper-beryllium (Cu–Be) alloy.

b) Metallic beryllium is used for making windows of X-rays tubes.

ii) Important uses of magnesium :

a) As magnesium is a light metal, its alloys with aluminium and zinc are used in aircraft construction.

eg. Elelctron(95% Mg + 5% Zn) and Magnalium (1 – 15%Mg + 85 - 99% A1) are used in

construction of aircrafts.

Magnalium is also used in the construction of light instruments. .



65s- Block Elements


b) In medicine, magnesium hydroxide [Mg(OH)2]in its suspension form is used as an antacid.

c) In toothpaste, one of the ingredients used is magnesium carbonate (MgCO3).

iii) Important uses of calcium :

a) Calcium is used to remove

1) air from vacuum tubes owing to its reactivity with oxygen and nitrogen at elevated

temperatures.

2) sulphur from petroleum

3) last traces of water from alcohol.

b) Extraction of some metal oxides using carbon is ineffective, therefore, in such situations calcium

is used as reducing agent.

c) Compounds of calcium such as limestone and gypsum are used as constituents of cement and

mortar.

iv) Important uses of barium :

a) BaSO4 being insoluble in H

2O and opaque to X-rays is used as 'barium meal' to scan the X-ray of

human digestive system.

b) Barium reacts with oxygen and nitrogen at high temperature, hence, it is used to remove air from

vacuum tubes.

Multiple Choice Questions

10.0 Prominent scientists

1. Potassium was discovered from caustic potash by

a) Arthur. H. Crompton

b) Johannes Bronsted

c) Sir Humphry Davy

d) G. N. Lewis

10.1 General introduction

2. The long form of the periodic table is divided into

blocks.

a) two b) three

c) four d) five

3. Which of the following is NOT an alkaline earth

metal ?

a) Beryllium b) Barium

c) Calcium d) Caesium

4. Francium is placed in the period of the periodic

table.

a) fourth b) fifth

c) sixth d) seventh

5. The common oxidation state for alkali metals is

a) + 2 b) + 1

c) + 3 d) + 4

6. All alkaline earth metals have valence electrons in

the outermost orbit.

a) one b) two

c) three d) four

7. Electronic configuration of potassium with respect

to nearest noble gases is.

a) [He]2s1 b) [Ne]3s1

c) [Ar]4s1 d) [Kr]5s1

10.2 Occurrence

8. Which of the following is radioactive alkali metal ?

a) Rubidium b) Caesium

c) Francium d) Beryllium

9. Which of the following element is rarest amongst

s-block elements?

a) Strontium b) Barium

c) Radium d) Calcium

10. Carnallite is.

a) KCI.MgCl2. 6H20

b) Na3AlF

6

c) Ca2B

6O

11.2H

2O

d) Ca2Mg

2Si

6O

22(OH)

2

10.3 Anomalous properties of lithium

11. The alkali metal that reacts with nitrogen directly

to form nitride is.

a) Li b) Na

c) K d) Rb

12. Which of the following compound is Not obtained

in the solid form ?

a) Calcium hydrogen carbonate

b) Potassium hydrogen carbonate

c) Sodium hydrogen carbonate

d) Lithium hydrogen carbonate

10.4 Diagonal relationship between lithium and

magnesium

13. Lithium shows diagonal relationship with

a) beryllium b) magnesium

c) calcium d) boron

14. The diagonal relationship between Li and Mg is

due to the similarity in

a) ionic sizes

b) Electronegativity value

c) polarizing power

d) all of the above



66s- Block Elements


15. Which of the following is FALSE ?

a) LiCI is soluble inethanol

b) MgO combines with excess

c) Carbonates of lithium and magnesium

decompose on heating to form oxides and

CO2.

d) Magnesium does not form solid hydrogen

carbonate

10.5 Periodic trends of alkali elements (metals)

(Group-l elements)


a) Alkali metals readily loose electron to produce

monovalent M+ ions.

b) In a group, from Li to Cs, atomic and ionic

radii increases with atomic number.

c) The monovalent ions of alkali metals are

larger in size than the parent atoms.

d) Ionization 'enthalpies decrease down the

group from Li to Cs.

17. Ionization enthalpy of Cs is ____kl/mol.

a) 152 b) 265

c) 376 d) 520

10.6 Chemical reactivity of alkali metals

18. Alkali metals are normally kept in.

a) kerosene oil b) toluene

c) water d) alcohol

19. The stability of the following alkali metal chlorides

follows the order.

a) LiCl > KCl > NaCl > CsCl

b) CsCl > KCl > NaCl > LiCl

c) NaCl > KCl > LiCl > CsCl

d) KCl > CsCl > NaCl > LiCl

20. Sodium reacts with water more vigorously than

lithium because it.

a) has higher atomic weight

b) is a metal

c) is more electropositive

d) is more electronegative

21. Which of the following is least stable ?

a) LiH b) NaH

c) KH d) CaH2

22. NaBH4 is powerful agent____agent.

a) Oxidising b) reducing

c) dehydrating d) bleaching

10.7 Important compounds of sodium

23. In the Solvay process, the chief products are

a) CaCO3 and Ca(HCO

3)

2

b) Na2CO

3 and NaHCO

3

c) Na2SO

4 and NaHSO

4

d) CaCl2 and Ca(NO3)

2

24. The by-product in ammonia soda process is

a) calcium hydroxide

b) ammonium hydroxide

c) calcium chloride

d) calcium carbonate

25. Washing soda is___

a) NaOH b) Na2CO

3.H

2O

c) Na2CO

3 10H

2O d) NaHCO

3

26. ____is used in medicines as an antacid.

a) Sodium carbonate

b) Sodium hydroxide

c) Sodium chloride

d) Sodium hydrogen carbonate

27. Sodium chloride when heated with conc. H2SO

4

and MnO2, liberates___ gas.

a) carbon monoxide

b) carbon dioxide

c) chlorine

d) hydrogen

28. In Castner's process for preparation of sodium

hydroxide, ____ is subjected to electrolysis.

a) NaCl b) NaOH

c) Na2O d) Na

2CO

3

29. is used in salting process of soap.

a) Washing soda

b) Caustic soda

c) Baking soda

d) Sodium chloride

10.8 Uses of alkali metals

30. Toughened bearings are made using ____alloy

a) Na-Pb b) Li-Pb

c) Li-Al d) Li-Mg

31. In fast breeder nuclear reactors is used as a coolant.

a) lithium metal

b) liquid sodium metal

c) liquid potassium metal

d) caesium metal

32. is an excellent absorbent of carbon dioxide.

a) KO2

b) KCl

c) KOH d) KHCO3

10.9 Biological importance of sodium and

potassium

33. Deficiency of sodium leads to__

a) atrophy of muscle and testis

b) retarted bone growth

c) lung infection

d) all of these

34. Excess of sodium leads to__

a) hypertension

b) hypertrophy' of kidneys

c) paralysis of muscles

d) scarring of heart



67s- Block Elements


35. Which ofthe following is FALSE ?

a) Sodium is the major cation in the blood

plasma of vertebrates.

b) Na+ ions depress the activity of muscle

enzyme.

c) K+ ions permit the heart muscles to relax

between the beats.

d) Na+ is especially an enzyme activator.

10.10 Periodic trends of alkaline earth metals

(Group-2 elements)

36. Which of the following group-2 element is NOT

known as alkaline earth metal ?

a) Be b) Ca

c) Ba d) Sr

37. The first ionization enthalpies of alkaline earth

metals are than those of the corresponding alkali

metals.

a) higher b) lower

c) same d) None of these

10.11 Chemical reactivity

38. Which of the following alkaline earth metal does

NOT react with water ?

a) Be b) Mg

c) Ca d) Sr

39. Which of the following is INCORRECT ?

a) Beryllium is kinetically inert to oxygen but

reacts with it in powdered form.

b) Magnesium is more electropositive than

beryllium.

c) Barium reacts with pure oxygen to form

barium oxide.

d) The affinity of alkaline earth metals towards

oxygen increases in the order

Be < Mg < Ca < Sr < Ba < Ra.

40. Which of the following hydrides is called hydrolith ?

a) BeH2

b) CaH2

c) SrH2

d) BaH2

10.12 Anomalous properties of beryllium

41. Oxides and hydroxides of alkaline earth metals

except beryllium are _____in nature.

a) acidic b) basic

c) amphoteric d) neutral

42. Among the alkaline earth metals, the element

forming predominantly covalent compound is

a) barium b) strontium

c) calcium d) beryllium

43. Beryllium does NOT show coordination number

more than.

a) four b) five

c) six d) seven

44. Metallic is used for making windows of X-rays

tubes.

a) Be b) Mg

c) Ba d) Ca

45. Which of the following represents composition of

magnalium ?

a) 95% Mg + 5% Zn

b) 99% Mg + 1% Zn

c) 15% Mg + 85% Al

d) 30% Mg + 70% Al

46. Which of the following alkali metal is used to

remove sulphur from petroleum ?

a) Beryllium b) Calcium

c) Barium d) Magnesium


a) Magnesium is a light metal.

b) Beryllium is used to remove air from vacuum

tubes.

c) Barium metal is used to scan the x-ray.

d) Calcium is used as a reducing agent in the

extraction of metal oxide.

10.14 Diagonal relationship between beryllium and

aluminium

48. The ionic radius of Be is

a) 13 pm b) 26 pm

c) 31 pm d) 62 pm

49. Beryllium carbide on hydrolysis gives

a) methane

b) ethane

c) beryllium hydrate

d) beryllium oxide

50. Which of the following is INCORRECT ?

a) BeO and Be(OH)2 are amphoteric in nature.

b) Be(OH)2 dissolves in excess alkali to form

beryllate ion.

c) Aluminium carbide on hydrolysis gives

methane.

d) BeCh acts as Lewis base.

10.15 Important compounds of calcium

51. Slaked lime is.

a) CaCO3

b) CaO

c) Ca(OH)2

d) Ca(C2O

4)

52. Which of the following is cheapest, form of alkali?

a) Mg(OH)2

b) CaO

c) Be(OH)2

d) All of these

53. The main constituent in marble slate is

a) CaCO3

b) CaCl2

c) CaO d) Ca(OH)2

10.16 Biological importance of magnesium and

calcium



68s- Block Elements


54. Magnesium is present in.

a) haemoglobin b) chlorophyll

c) vitamin B12

d) ascorbic acid

55. Deficiency of magnesium causes.

a) rickets

b) osteoporosis

c) neuromuscular irritation

d) all of these

Answer Keys

1. c) 2. c) 3. d) 4. d) 5. b) 6. b) 7. c) 8. c) 9. c) 10. a)

11. a) 12. d) 13. b) 14. d) 15. b) 16. c) 17. c) 18. a) 19. b) 20. c)

21. d) 22. b) 23. b) 24. c) 25. c) 26. d) 27. c) 28. a) 29. d) 30. b)

31. b) 32. c) 33. d) 34. a) 35. d) 36. a) 37. a) 38. a) 39. c) 40. b)

41. b) 42. d) 43. a) 44. a) 45. c) 46. b) 47. b) 48. c) 49. a) 50. d)

51. c) 52. b) 53. a) 54. b) 55. c)





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s- Block Elements

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