The s-Block Elements
1) What are the common physical features of alkali metals?
Solution-
i) Common physical features of alkali metals:
i) Alkali metals are silvery white, soft and light metals.
ii) They have low density , which increases from Li to Cs down the group.
iii) The general outer electronic configuration of all alkali metals in ns1 (n= 2 to 7).
iv) The atoms of alkali metal have large atomic size in a particular period. The atomic size increases from
Li to Cs down the group due to addition of extra shell from element to the next.
v) They have low ,melting and boiling points due to weak metallic bonding.
vi) They have low ionisation enthalpy due to large atomic size. The ionization enthalpy decreases down the
group from Li to Cs as atomic size increases.
vii) The hydration enthalpies of alkali metal ions decreases with increases in ionic size.
Li+
> Na+
> K+ >Rb
+ > Cs
+
ii) Common chemical features of alkali metals:
i) Alkali metals are highly reactive due to low ionisation enthalpy and large atomic size. The reactivity
decreases down the group as ionization enthalpy decreases.
ii) Alkali metal tarnish in dry air due to the formation of oxides, which, in turn, reacts with moisture to
form hydroxides.
iii) Alkali metals burn vigorously in oxygen forming oxides. Lithium forms monoxide, sodium forms
peroxide and other form superoxides.
iv) They react with water to form metal hydroxides and liberate hydrogen gas.
2M + 2H2O →2MOH + H2
(M= Li, Na, K, Rb, Cs)
iv) Alkali metals react vigorously with halogens to form ionic halides of type MX (except for lithium ,
which forms covalent halides)
CONTACT US @ 08889388421ABHYAAS CLASSES BY ROHIT SIR
ABHYAAS CLASSES BY ROHIT SIRwww.abhyaasclasses.in
ABHYAAS CLASSES
BY R
OHIT SIR
2M + X2 →2MX
(M= Li, Na, K, Rb, Cs)
2) Discuss the general characteristics and gradation in properties of alkaline earth metals.
Solution-
General characteristics of alkaline earth metals and gradation in properties:
i) All the alkaline earth metals have a general outer electronic configuration of ns2 (n= 2 to 7).
ii) The atomic and ionic radii of the alkaline earth metals are smaller than those of the corresponding alkali
metals belonging to the same period due to an increase in the nuclear charge. The atomic and ionic radii
increase from Be to Ra due to the addition of shells from one element to the next, as the atomic number
increases down the group.
iii) The alkaline earth metals have low ionization enthalpies due to to large atomic size of their atoms.
Their ionisation enthalpies decrease down the group due to an increases in atomic size.
iv) The hydration enthalpies of alkaline earth metal ions decrease with an increase in ionic size down the
group.
Be2+
> Mg2+
> Ca2+
>Sr2+
> Ba2+
3) Why are alkali metals not found in nature?
Solution
Alkali metals are not found in a free state in nature due to their high reactivity. They always exist in a
combined state with another element in the form of mineral s and ores in the earth’s crust.
4) Find out the oxidation state of sodium in Na2O2.
Solution
In Na2O2 (sodium peroxide) each oxygen has -1 oxidation state due to peroxy bond.
∴Theoxidationstateofsodiumis�1inNa2O2 .
Let the oxidation state of Na be x . Then
2x -2 = 0
CONTACT US @ 08889388421ABHYAAS CLASSES BY ROHIT SIR
ABHYAAS CLASSES BY ROHIT SIRwww.abhyaasclasses.in
ABHYAAS CLASSES
BY R
OHIT SIR
2x = 2
x= 2/2 = +1
∴OxidationstateofNainNa2O2 is +1.
5) Explain why is sodium less reactive than potassium.
Solution
Sodium is less reactive than potassium, due to its bigger size and low ionisation enthalpy. Potassium has a
greater tendency to lose an electron and get oxidised than sodium.
6) Compare the alkali metals and alkaline earth metals with respect to ionization enthalpy.
Solution
i) Ionization enthalpy:
Alkaline metals Alkaline earth metals
The ionisation enthalpy of
alkali metals is low due to
their large atomic size.
Example :
Li -520 kJ mol-1
Na – 496 kJ mol-1
The ionisation enthalpy of
alkaline earth metals is also
low, but they are higher than
alkaline earth metals
corresponding to the alkali
metals of the same period
due to large nuclear change
and their small size
compared to alkali metals.
Example:
Be- 899 kJ mol-1
Mg- 737 kJ mol-1
ii) Basicity of oxides:
Alkaline metals Alkaline earth metals
The oxides of alkali metals
are strongly basic and form
very strong bases when
dissolved in water.
Example:
Na2O + H2O →2NaOH
K2O + H2O → 2KOH
The oxides of alkaline earth
metals are basic, but not as
strongly basic as alkali metal
oxides. The oxides of
alkaline earth metals are less
basic than alkaline metal
oxides.
Example :
CONTACT US @ 08889388421ABHYAAS CLASSES BY ROHIT SIR
ABHYAAS CLASSES BY ROHIT SIRwww.abhyaasclasses.in
ABHYAAS CLASSES
BY R
OHIT SIR
CaO + H2O →Ca (OH)2
BaO + H2O →Ba (OH)2
iii) Solubility of hydroxides:
Alkaline metals Alkaline earth metals
The hydroxides of alkali
metals are highly soluble in
water:
Example :
NaOH , KOH
The hydroxides of alkaline
earth metals are less or
sparingly soluble in water.
The solubility increases
down the group as the atomic
number of the elements
increases.
Example:
Ca(OH)2 , Mg (OH)2
7) In what ways lithium shows similarities to magnesium in its chemical behaviour?
Solution
i) Li and Mg, both react slowly with water.
ii) The oxides and hydroxides of Li and Mg are less soluble, and the hydroxides decompose on heating.
iii) Li and Mg, both combine with nitrogen directly to form nitrides, Li3N and Mg3N2.
iv) Li and Mg , do not form superoxides on combining with excess oxygen.
v) The carbonates of Li and Mg are less stable and decompose easily on heating to form oxide with the
liberation of CO2 gas.
vi) Li and Mg do not form solid hydrogen carbonates.
vii) LiCl and MgCl2 are deliquescent and crystallise, from their aqueous solution as hydrates, LiCl.2H2O
and MgCl2.8H2O.
8) Explain why can alkali and alkaline earth metals not be obtained by chemical reduction methods?
CONTACT US @ 08889388421ABHYAAS CLASSES BY ROHIT SIR
ABHYAAS CLASSES BY ROHIT SIRwww.abhyaasclasses.in
ABHYAAS CLASSES
BY R
OHIT SIR
Solution
Alkali and alkaline earth metals cannot be obtained by chemical reduction methods as they are strong
reducing agents and other reducing agents cannot reduce them . this is due to the low ionization potential of
these elements and their tendency to lose electrons easily. This is evident from their large negative
reduction potential value.
9) Why are potassium and caesium, rather than lithium used in photoelectric cells?
Solution
The atomic size of lithium is small, because of which the electron requires more energy to be removed
from its valence shell than potassium and caesium. Therefore, potassium and caesium which can lose
valence electrons by absorbing light of less energy, are used in photoelectric cells.
10) When an alkali metal dissolves in liquid ammonia the solution can acquire different colours. Explain
the reasons for this type of colour change.
Solution
When an alkali metal dissolves in liquid ammonia, the solution acquires deep blue colour, because the
ammoniated electron absorb energy in the visible region of light.
In a concentrated solution , the blue colour changes to bronze.
M + (x+y) NH3 →[M(NH3)x]+ + [e(NH3)y]
-
Ammoniated electron
11) Beryllium and magnesium do not give colour to flame where as other alkaline earth metals do so why?
Solution
The electrons in Be and Mg atoms are strongly bound and cannot be excited by the flame due to their
small size compared to other elements. Therefore , Be and Mg do not give colour to the flame.
12) Discuss the various reactions that occur in the Solvay process.
Solution
The Solvay process is used to prepare sodium carbonate (washing soda).
CONTACT US @ 08889388421ABHYAAS CLASSES BY ROHIT SIR
ABHYAAS CLASSES BY ROHIT SIRwww.abhyaasclasses.in
ABHYAAS CLASSES
BY R
OHIT SIR
The principal reactions that take place in the Solvay ammonia process are:
i) 2NH3 +H2O+CO2→(NH4)2CO3
ii) →(NH4)2CO3+ H2O+CO2→2NH4HCO3
iii) NH4HCO3 +NaCl→ NH4Cl + NaHCO3
iv) 2 NaHCO3→ Na2CO3 + H2O+CO2
13) Potassium carbonate cannot be prepared by Solvay process. Why?
Solution
Potassium carbonate cannot be prepared by the Solvay process, as potassium hydrogen carbonate is soluble
in water , and cannot b precipitated by adding of ammonium hydrogen carbonate to a saturated solution of
potassium chloride.
14) Why is Li2CO3 decomposed at a lesser temperature whereas Na2CO3 at higher temperature.
Solution
Li2CO3 decomposes at a lower temperature due to the small size of the Li+
ion . The small size of Li+
,
makes the lattice of Li2O more stable than that of Li2CO3 . This results in the decomposition of Li2CO3 to
Li2O and CO2 . Therefore, Li2CO3 is not thermally stable. On the other hand, Na2CO3, due to its larger size,
forms a thermally stable lattice.
15) Compare the solubility and thermal stability of the compounds of the alkali metal with those of the
alkaline earth metal nitrates.
Solution
i)
Alkaline metals Alkaline earth metals
Solubility :
The nitrates of alkali metals
are soluble in water. The
water solubility increases
down the group as the lattice
enthalpy decrease rapidly
The nitrates of alkaline earth
metal decompose on heating
to form metal oxide with the
liberation of nitrogen dioxide
and oxygen.
CONTACT US @ 08889388421ABHYAAS CLASSES BY ROHIT SIR
ABHYAAS CLASSES BY ROHIT SIRwww.abhyaasclasses.in
ABHYAAS CLASSES
BY R
OHIT SIR
than the hydration enthalpy.
Thermal stability:
The nitrates of alkali metals,
except lithium, decompose
on heating , to form the
corresponding nitrites with
the evolution of oxygen gas.
However, lithium nitrate, on
heating, decomposes to form
lithium oxide, nitrogen
dioxide and oxygen.
2MNO3 →
2MNO2 + O2
Alkali metal nitrite Alkali
metal nitrate
2M(NO3)2 → 2MO
+ 4NO2 + O2
Alkali metal nitrate Alkali
metal oxide
(M=Be, Mg, Ca, Sr, Ba)
ii) Carbonates:
iii)Sulphates:
Alkaline metals Alkaline earth metals
Solubility :
Alkali metal carbonates are
soluble in water.
Thermal stability:
Alkali metal carbonates,
except lithium carbonate, are
highly stable, do not
decompose on heating , and
the stability increases down
the group.
Lithium carbonate
decomposes to form lithium
oxide and carbon dioxide on
heating.
2Li2CO3 → Li2O
+ O2
Lithium carbonate
Lithium monoxide
Solubility :
Alkaline earth metal
carbonates are insoluble in
water.
Thermal stability:
Alkaline earth metal
carbonates decompose on
heating, to from the
corresponding metal oxide ,
with the liberation of carbon
dioxide. The thermal stability
increases down the group
with an increase in cationic
size.
MCO3 →MO + CO2
(M=Be, Mg, Ca, Sr, Ba)
CONTACT US @ 08889388421ABHYAAS CLASSES BY ROHIT SIR
ABHYAAS CLASSES BY ROHIT SIRwww.abhyaasclasses.in
ABHYAAS CLASSES
BY R
OHIT SIR
16) a)Starting with sodium chloride how would you proceed to prepare
i) Sodium metal ii) Sodium hydroxide
Solution
i) Sodium metal from sodium chloride:
Sodium metal can be obtained by the electrolysis of molten or fused NaCl (Down’s process). Sodium metal
is deposited at the cathode, while chlorine is liberated at the anode.
2NaCl(l) →2Na(s) +Cl2 (g)
ii) Sodium hydroxide from sodium chloride:
Sodium hydroxide is obtained by the electrolysis of aqueous solution of NaCl (brine solution) (Nelson cell
process). Sodium hydroxide is obtained and H2 gas is liberated at the cathode. Cl2 gas is liberated at the
anode.
2NaCl (aq) + 2H2O(l) →2NaOH (aq) + H2 +Cl2(g)
b) Starting with sodium chloride how would you proceed to prepare
iii) Sodium peroxide iv) Sodium carbonate.
Solution
iii) Sodium peroxide from sodium chloride:
Alkaline metals Alkaline earth metals
Solubility :
Alkali metal sulphates are
soluble in water.
Thermal stability:
Alkali metal sulphates ,
except lithium sulphate, are
thermally stable and do not
decompose on heating.
Lithium sulphate
decomposes on heating to
form lithium monoxide, with
the liberation of sulphur
dioxide and oxygen.
2LiSO4 → 2Li2O +2SO2 +
O2
Solubility :
BeSO4 and MgSO4 are
soluble in water and the
solubility decreases from
CaSO4 to BaSO.
Thermal stability:
Alkaline earth metal
sulphates decompose on
heating to form the
corresponding metal oxide
with the liberation of sulphur
dioxide and oxygen.
2MSO4 →2MO + 2SO2 +O2
(M= Be, Mg, Ca, Sr, Ba)
CONTACT US @ 08889388421ABHYAAS CLASSES BY ROHIT SIR
ABHYAAS CLASSES BY ROHIT SIRwww.abhyaasclasses.in
ABHYAAS CLASSES
BY R
OHIT SIR
Sodium is obtained by electrolysis of fused NaCl . Sodium, when burnt in oxygen, froms sodium peroxide.
2Na + O2 → Na2 O2
iv) Sodium carbonate from sodium chloride:
Sodium carbonate is obtained by the action of ammonia and CO2 on an aqueous NaCl solution.
2NH3 + H2O +CO2 →(NH4)2CO3
(NH4)2CO3+ H2O +CO2 → 2NH4HCO3
NH4HCO3 +NaCl → NH4Cl + NaHCO3
Sodium bicarbonate on heating forms sodium carbonate.
NaHCO3 → Na2CO3 + CO2 +H2O
17) a) What happens when
i) magnesium is burnt in air ii) quick lime is heated with silica?
Solution
i) When magnesium is burnt in the air, it burns with a dazzling light with emission U.V
radiations and forms magnesium oxide and magnesium nitride.
5Mg(s) + O2(g) +N2(g) →2MgO (s) + Mg3N2 (s)
ii) When quick lime is heated with silica , it forms calcium silicate.
CaO (s) + SiO2 (s) →CaSiO3 (s)
b) What happens when
i) chlorine reacts with slaked lime iv) calcium nitrate is heated
iii) When chlorine reacts with slaked lime, it forms bleaching powder.
Ca(OH)2 + Cl2 → CaOCl2 +H2O
CONTACT US @ 08889388421ABHYAAS CLASSES BY ROHIT SIR
ABHYAAS CLASSES BY ROHIT SIRwww.abhyaasclasses.in
ABHYAAS CLASSES
BY R
OHIT SIR
iv) When calcium nitrate is heated, it undergoes decomposition with the evolution of
nitrogen dioxide gas.
2Ca(NO3)2(s) →2 CaO(s) + 4NO2 (g) + O2(g)
18) Describe two uses of the following:
i) Caustic soda ii) Sodium carbonate iii) Quick lime
Solution
i) Two uses of caustic soda:
a) It is used in the manufacture of soap.
b) It is used in the extraction of aluminium from bauxite, in the refining of bauxite.
ii) Two uses of sodium carbonate:
a) It is used in water softening and as a cleaning agent.
b) It is used in the manufacture of glass and braa.
iii) Two uses of quick lime:
a) It is used in the manufacture of cement.
b) It is used in the purification of sugar.
19) Draw the structure of i) BeCl2 (vapour) ii) BeCl2 (solid)
Solution
i) BeCl2 (vapour):
BeCl2 has a linear structure with 180° bond angle in vapour state.
ii) BeCl2 (solid)
CONTACT US @ 08889388421ABHYAAS CLASSES BY ROHIT SIR
ABHYAAS CLASSES BY ROHIT SIRwww.abhyaasclasses.in
ABHYAAS CLASSES
BY R
OHIT SIR
Solid state BeCl2 has a polymeric chain structure with chlorine bridges.
20) The hydroxides and carbonates of sodium and potassium are easily soluble in water,
while the corresponding salts of magnesium and calcium are sparingly soluble in water.
Explain.
Solution
The solubility of an ionic compound in water depends on its lattice energy and hydration
energy. The lattice energy of the hydroxides and carbonates , of sodium and potassium is
less than their hydration energy, due to the large size of their cations. Therefore, the
hydroxides and carbonates of sodium and potassium are soluble in water. On the other
hand, the lattice energy of the hydroxides and carbonates, of magnesium and calcium is
higher than the hydration energy, due to the small size of their cations and relativley more
magnitude of the charge. Therefore, the hydroxides and carbonates , of magnesium and
calcium are sparingly soluble in water.
21) i) Describe the importance of the Limestone.
Solution
i) Limestone is calcium carbonate(CaCO3).
Importance:
a) It is used as building material in the form of marble.
b) It is used in the manufacture of quicklime .
c) It is used in flux in the extraction of metals in metallurgy.
d) It is used as an antacid, and as a mild abrasive in tooth paste.
CONTACT US @ 08889388421ABHYAAS CLASSES BY ROHIT SIR
ABHYAAS CLASSES BY ROHIT SIRwww.abhyaasclasses.in
ABHYAAS CLASSES
BY R
OHIT SIR
e) It is a constituent of chewing gum, and is used as filler in cosmetics.
ii) Describe the importance of the Cement.
Solution
Cement:
Cement is an important building material. It is also called as Portland cement.
Composition of cement:
CaO(50-60%),
SiO2(2-25%),
Al2O3(5-10%),
MgO (2-3%)
H2O3(1-2%)
and SO3(1-2%)
Importance:
Cement is a very important commodity of material necessity for any country after iron and
steel.
a) It is used to make concrete and reinforced concrete.
b) It is used in plastering and in the construction of bridges, dams and buildings.
iii) Describe the importance of the Plaster of Paris.
Solution
Plaster of Paris
Hemihydrate of calcium sulphate is plaster of Paris. Its chemical formula is CaSO4.1/2H2O
Importance:
CONTACT US @ 08889388421ABHYAAS CLASSES BY ROHIT SIR
ABHYAAS CLASSES BY ROHIT SIRwww.abhyaasclasses.in
ABHYAAS CLASSES
BY R
OHIT SIR
a) It is used as building material.
b) It is used in the plastering of walls and for interior decoration.
c) It is used as plaster for joining fractured ones and also used in dentistry.
d) It is used for making casts of statues and busts.
22) Why are lithium salts commonly hydrated and those of the other alkali ions usually
anhydrous?
Solution
Because of its very small size, a lithium atom has the tendency to get hydrated . Therefore,
lithium salts are hydrated, when they come in contact with moisture. On the other hand, the
cations of other alkali metal ions are very large and cannot be hydrated easily. Therefore ,
other alkali metal salts are anhydrous.
23) Why are LiF almost insoluble in water , whereas LiCl soluble not only in water but also
in acetone?
Solution
LiF is insoluble in water due its high lattice enthalpy, which is due to the very small size of
the F- ion. On the other hand, LiCl is soluble in water due to the relatively low lattice
enthalpy, ehich is due to the large size of Cl- ions. It is soluble in acetone because of dipolar
attractions created by the polar nature of acetone.
24) Explain the significance of sodium, potassium , magnesium and calcium in biological
fluid.
Solution
Biological importance o sodium and potassium:
Sodium and potassium are considered as microelements, that are present in their ionic form
in body fluids.
CONTACT US @ 08889388421ABHYAAS CLASSES BY ROHIT SIR
ABHYAAS CLASSES BY ROHIT SIRwww.abhyaasclasses.in
ABHYAAS CLASSES
BY R
OHIT SIR
a) Sodium and potassium ions transmit nerve signals.
b) They regulate the flow of water across cell membranes.
c) They also transport sugars and amino acids into the cells.
d) They activate the enzymes that carry out regular metabolic activities, like oxidation of
glucose to produce ATP.
e) Sodium and potassium ions are present in high concentration on either side of the cell
membrane. These ions are continuously exchanged between the cell membrane by a
discriminating mechanism called sodium-potassium pump.
This consumes one-third of the ATP of a resting animal.
Biological importance of magnesium and calcium:
A healthy adult body contains about 25g of Mg and 1200 g of Ca.
Importance of magnesium:
a) Magnesium is the cofactor for all enzymes that utilise ATP in phosphate transfer.
b) The green pigment is plants, chlorophyll , has magnesium as the central metal ion.
Chlorophyll absorbs sunlight and produces food from CO2 and H2O by a process called
photosynthesis.
Importance of calcium :
a) Nearly 99% of the calcium in the body is in the bones and teeth, which support the
muscular mass of the body.
b) It plays a major role in neuromuscular function and inter neuronal transmission.
c) It also plays an important role in cell membrane integrity and blood coagulation.
25) What happens when:
i) Sodium metal is dropped in water?
ii) Sodium metal is heated in free supply of air?
iii) Sodium peroxide dissolves in water?
CONTACT US @ 08889388421ABHYAAS CLASSES BY ROHIT SIR
ABHYAAS CLASSES BY ROHIT SIRwww.abhyaasclasses.in
ABHYAAS CLASSES
BY R
OHIT SIR
Solution
i) When sodium metal is dropped in water, sodium hydroxide is formed.
The reaction takes place with a hissing sound and is an explosive reaction. The metal
catches fire because the hydrogen that evolved during the reaction is highly combustible
and catches fire.
2Na + 2H2O → 2NaOH + H2
ii) When sodium metal is heated in free supply of air sodium peroxide is formed.
2Na + O2 → Na2 O2
iii) When sodium peroxide dissolves in water, oxygen gas is evolved with the formation of
sodium hydroxide.
2Na2 O2 + 2H2O → 4NaOH + O2
26) Comment of each of the following observations:
a) The mobilities of the alkali metal ions in aqueous solution are
Li+
< Na+
< K+
<Rb+
< Cs+.
b) Lithium is the only alkali metal to form nitride directly.
c) E- for M
2+ (aq) + 2e
− → M(s) (where M= Ca, Sr or Ba) is nearly constant.
Solution
a) The mobility of alkali meta ions in their aqueous solutions depends on the size of the
cation and hydration. As smaller cation is hydrated to a large extent, and hydrated Li+
is
large. Therefore, its mobility is the least. As the size of the cation increases, its hydrated ion
size decreases and the mobility increases.
Li+
< Na+
< K+
<Rb+
< Cs+.
CONTACT US @ 08889388421ABHYAAS CLASSES BY ROHIT SIR
ABHYAAS CLASSES BY ROHIT SIRwww.abhyaasclasses.in
ABHYAAS CLASSES
BY R
OHIT SIR
b) Because of its very strong reducing nature, lithium can easily react with nitrogen to form
nitride. However, due to their low reducing nature, other alkali metals do not combine with
nitrogen.
3Li + N2 →Li3N2
c) The value of E° depends on sublimation enthalpy, ionisation enthalpy and hydration
enthalpy. For the given metals, the overall magnitude of E° remains the same. Therefore,
metals have nearly the same reducing strength.
27) State as to why:
a) A solution of Na2CO3 is alkaline?
b) Alkaline metals are prepared by electrolysis of their fused chlorides?
c) Sodium is found to be more useful then potassium?
Solution
a) Na2CO3 is a salt of a weak acid(H2CO3) and a strong base (NaOH) . The aqueous solution
of Na2CO3 is alkaline due to anionic hydrolysis.
Na2CO3 + 2H2O → 2NaOH + H2CO3
b) Alkali metals are very strong reducing agents. No reducing agents are available to reduce
them. Therefore, they cannot be obtained by normal chemical reduction methods. Hence,
alkali metals are prepared by the electrolysis of their fused chlorides.
c) Sodium is more abundant and also less reactive than potassium. The reactions of sodium
with other substances can be controlled . Therefore, sodium is more useful than potassium.
28) Write balanced equations for reactions between:
a) Na2O2 and water b) Na2O and CO2 c) KO2 and water
Solution
a) 2Na2O2 + 2H2O → 4NaOH + O2
CONTACT US @ 08889388421ABHYAAS CLASSES BY ROHIT SIR
ABHYAAS CLASSES BY ROHIT SIRwww.abhyaasclasses.in
ABHYAAS CLASSES
BY R
OHIT SIR
b) 2KO2 +2H2O → 2KOH + H2O2 + O2
c) Na2O + CO2 → Na2CO3
29) How would you explain the following observation?
i) BeO is almost insoluble but BeSO4 is soluble in water BaO.
ii) BaO is soluble but BaSO4 is insoluble in water.
iii) LiI is more soluble than KI is ethanol.
Solution
i) BeO is insoluble because its lattice enthalpy is high as compared to BeSO4.
This is due to the small size of the O2-
ion as compared to BeSO4 . The high lattice energy
opposes the solubility of a substance in water. Therefore, BeO is insoluble in water, while
BeSO4 due to its low lattice enthalpy , is soluble in water.
ii) BaO is soluble, because of its lattice enthalpy is less than the hydration enthalpy due to
the large size of the Ba2+
ion. In the case of BaSO4 , due to the large size of SO42-
ion, Ba2+
ion is masked and is not hydrated. In BaSO4 , the lattice enthalpy is more than the hydration
enthalpy. Therefore, BaSO4 is insoluble in water.
iii) KI is ionic in nature, while LiI is covalent. Due to its small size, the Li+ ion, polarises
the electron cloud on the I-ion to a greater extent. Due to its covalent nature, LiI, is soluble
in ethanol, while due to its ionic nature, KI, is insoluble in ethanol.
30) Which of the alkali metal is having least melting point?
a) Na b)K c)Rb d) Cs
Solution
d) Cs(Caesium)
As the atomic size increases down a group, the strength of the metallic bond decreases, and
the melting point of the elements also decreases. Therefore, Cs, being the largest , ahs the
lowest melting point.
CONTACT US @ 08889388421ABHYAAS CLASSES BY ROHIT SIR
ABHYAAS CLASSES BY ROHIT SIRwww.abhyaasclasses.in
ABHYAAS CLASSES
BY R
OHIT SIR
31) Which of the following alkali metals gives hydrated salts?
a) Li b) Na c) K d) Cs
Solution
a) Li(Lithium)
Li+ ion can attract water molecules easily than any other alkali metal ion, because of its
small size. Therefore, lithium forms hydrated salts.
32) Which of the alkaline earth metal carbonates is thermally the most stable?
a) MgCO3 b) CaCO3 c) SrCO3 d) BaCO3 e) BeCO3
Solution
d) BaCO3
BaCO3 is thermally more stable, as both Ba2+
ion and CO32-
ions are large leading to the
formation of a stable lattice.
CONTACT US @ 08889388421ABHYAAS CLASSES BY ROHIT SIR
ABHYAAS CLASSES BY ROHIT SIRwww.abhyaasclasses.in
ABHYAAS CLASSES
BY R
OHIT SIR