42617228-8-Salts

FORM 4 CHEMISTRY CHAPTER 8: SALTS________________________________________________________________________________________________

CHAPTER 8: SALTS

A. SALTS

Learning Outcomes You should be able to: state examples of salts used in daily life explain the meaning of salt identify soluble and insoluble salts describe the preparation of soluble salts describe the purification of soluble salts by recrystallisation list physical characteristics of crystals describe the preparation of insoluble salts write chemical and ionic equations for reactions used in the preparation of

salts design an activity to prepare a specified salt construct ionic equations through the continuous variation method solve problems involving calculation of quantities of reactants or products in stoichiometric

reactions

Activity 1: Definition and uses of salts

1. A salt is a ……………………..……… formed when the ……………….. ion in an …………… is

replaced by a ……………. ion or an ………………….. ion.

2. Match the following salts with their uses.

Salts UsesBarium sulphate, BaSO4 Pesticide Hydrated calcium sulphate, CaSO4

Bleaching agent

Iron sulphate heptahydrate, FeSO4.7H2O

Paint for yellow line on road

Ammonium nitrate, NH4NO3 Barium meals for patients who need to take X-ray of their stomach and intestine

Copper(II) sulphate, CuSO4 Nitrogenous fertilizerSodium chloride, NaCl Toothpaste Sodium hydrogen carbonate, NaHCO3

Iron pills for anaemia

Sodium nitrite, NaNO2 Baking powderSodium hypochlorite, NaOCl Food preservativeTin(II) fluoride SnF2 Flavouring agentBarium chromate(VI) Plaster of Paris for broken bone

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Activity 2: Identify soluble and insoluble salt

1. Complete the table below.

Compound Solubility in waterAmmonium saltsSodium and potassium saltsEthanoate saltsNitrate saltsChloride saltsSulphate saltsCarbonate saltsMetal oxidesMetal hydroxides

2. State whether each of the following salt is soluble or insoluble in water.

No Formula of salt Solubility in water ( , X )

No Formula of salt Solubility in water ( , X )

1 PbCO3 21 MgCO3

2 NaCl 22 KCl3 CaSO4 23 (NH4)2SO4

4 AgNO3 24 Cu(NO3)2

5 K2CO3 25 SnCO3

6 FeCl3 26 CaCl2

7 Na2SO4 27 BaSO4

8 NH4NO3 28 KNO3

9 CuSO4 29 Ag2CO3

10 PbCl2 30 MgCl2

11 ZnCO3 31 ZnSO4

12 Ca(NO3)2 32 Ba(NO3)2

13 Na2CO3 33 FeCO3

14 AgCl 34 NH4Cl15 PbSO4 35 Fe(NO3)3

16 Pb(NO3)2 36 MgSO4

17 (NH4)2CO3 37 BaCO3

18 HgCl2 38 ZnCl2

19 Na2SO4 39 FeSO4

20 NaNO3 40 Mg(NO3)2

2

Water

Na+

K+

NH4+

Ba2+

Ca2+

Pb2+Pb2+

Ag+

Hg2+NO3

-

Water

SO4 2-

Cl- CO3 2-

Na+

K+

NH4+

NO3 -Ba2+

Ca2+

Pb2+

Pb2+

Ag+

Hg+


Activity 3: Write the general equations for reactions used in the preparation of soluble salts

1. Complete these general equations for preparing soluble salts.

a. Acid + alkali …………… + …………………….

b. Acid + metal …………… + ……………………

c. Acid + base …………… + …………………….

d. Acid + metal carbonate …………........... + ……………… + ……………………….

Note: Reaction a is used to prepare soluble salts of ........................................, .................................... and ............................................. Reaction b, c and d are used to prepare soluble salts except ammonium salts, sodium salts or potassium salts.

2. Using the general equations in question 1, complete the following chemical equation. It may also be necessary to balance the equation.

a. NaOH + HCl ………………….. + ……………………….

b. Mg + H2SO4 …………… + …………………….

c. (i) CuO + HCl …………… + ……………………

(ii) Zn(OH)2 + HNO3 .............................. + .........................

d. MgCO3 + H2SO4 …………… + ……………… + ……………………….

3. Deduce the identity of the acid, metal, salt or other product by filling in the missing details in this table of preparation of soluble salt

Method of preparation Reactants Salt Formed Other

product

a) Acid + alkali ...................... + ……………… Sodium chloride Hydrogen

b) Acid + metal Zinc + sulphuric acid ……………………… …………….

c) Acid + base ……………… + ……………… Zinc sulphate Water

d) Acid + metal carbonate

……………… + ……………… Magnesium sulphate …………… + ..................

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Activity 4: Write out the procedure for the preparation of soluble salts of sodium, potassium and ammonium

Soluble salt Sodium chloride, NaCl

Name two chemical substances to prepare the salt

1. …………..…………………………..

2. ………………………………………

Chemical equation

Diagram Procedure

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Activity 5: Write out the procedure for the preparation of soluble salts (except sodium salts, potassium salts or ammonium salt)

Soluble salt Copper(II) sulphate, CuSO4


1. …………..…………………………..

2. ………………………………………Chemical equation

Diagram Procedure

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Activity 6: Write chemical and ionic equations for reactions used in the preparation of insoluble salts

1. Insoluble salts can be prepared by ………………….. reaction (double decomposition reaction). In this

reaction, two soluble salts solutions are mixed together to form the ....................... salt. The first soluble

salt solution contains the ..................... of the insoluble salt and the second soluble salt solution contains

the ...................... of the insoluble salt.

Soluble salt solution + Soluble salt solution Insoluble salt MX containing cation M+ containing anion X-

Chemical equation : AgNO3 (aq) + NaCl (aq) AgCl (s) + NaNO3(aq)

Ionic equation : Ag+ (aq) + Cl- (aq) AgCl (s)

2. Preparation of insoluble salts

Example 1: Barium sulphate, BaSO4

Solution 1: ……………………… Solution 2: ……….…....................

Chemical equation: ………………………………………………

Ionic equation: ……………………………………………………

Observation: A white precipitate is formed

Example 2: Copper(II) carbonate, CuCO3

Solution 1: ………………………………… Solution 2: ……………………………………….

Chemical equation : ………………………....................................

Ionic equation : ……………………………………………………....

Observation : A ……………….. precipitate is formed

Example 3: Lead(II) chromate(VI), PbCrO4

Solution 1: ……………………………………. Solution 2: …………………………………............

Chemical equation : …………………………………………

Ionic equation : …………………………………………….

Observation : A ………………............... precipitate is formed

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Activity 7: Describe the preparation of insoluble salts

Insoluble salt Lead(II) iodide, PbI2


1. …………..…………………………..

2. ………………………………………

Chemical equation

Ionic equation

Diagram Procedure

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Activity 8: Physical characteristics of crystals

Complete the physical characteristics of crystals in the spaces given below

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Activity 9: Construct ionic equation for the formation of lead(II) chromate(VI) using the continuous variation method

Figure 1

Figure 1 shows seven test tubes for the reaction between lead(II) nitrate Pb(NO3)2 0.5 mol dm-3 and potassium chromate(VI) K2CrO4 0.5 mol dm-3.

(a) (i) Using a ruler, measure the height of lead(II) chromate(VI) precipitate formed. Record the readings in Table 1.

Test tube 1 2 3 4 5 6 7

Volume of lead(II) nitrate solution /cm3 5.00 5.00 5.00 5.00 5.00 5.00 5.00

Volume of potassium chromate(VI) solution

/cm31.00 2.00 3.00 4.00 5.00 6.00 7.00

Height of precipitate / cm

Table 1

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Test tube 2… 2.00.cm3 of potassium chromate (VI solution), test tube 3…3.00 cm3 varying the volumes of potassium chromate(VI) solution .........

Fixed the volumes of lead (II) nitrate solution at 5.00 cm3.

1 2 3 4 5 6 7


(b) Based on Table 1, draw a graph of the height of the precipitate against volume of potassium chromate (VI) solution on the graph paper.

(c) On the graph that you have drawn in (b), (i) mark and write the minimum volume of potassium chromate(VI) solution needed for complete reaction

with 5.00 cm3 of lead(II) nitrate solution 0.5 mol dm-3.

(ii) Calculate the number of moles of chromate(VI) ions that has reacted with 1 mole of lead(II) ions.

(iii) Write the ionic equation for the formation of lead(II) chromate(VI).

………………………………………………………………………………………………………………(d) What can you observe about the height of the precipitate in Figure 1?

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………..(e) What is your inference based on your answer in (d)?

……………………………………………………………………………………………………………….

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FORM 4 CHEMISTRY CHAPTER 8: SALTS________________________________________________________________________________________________Activity 10: Solve problems involving calculation of quantities of reactants or products in stoichiometric reactions

Example 1: A student prepares copper (II) nitrate by reacting copper (II) oxide with 100 cm3

1.5 mol dm-3 nitric acid. Calculate the mass of copper (II) oxide needed to react completely with the acid. [Relative atomic mass: Cu, 64; O, 16]

Solution:

Chemical equation: CuO + 2HNO3 Cu(NO3)2 + H2O Mole ratio : 1 mole 2 mole 1 mole 1 mole Number of mole of CuO = 1 x Number of moles of HNO3 2

Number of mole of CuO = 1 x 0.15 = 0.075 mole 2

Mass of CuO = 0.075 x (64 + 16) = 6 g

Question:

1. Excess zinc powder is added to react completely with 50 cm3 of 2.0 mol dm-3 hydrochloric acid.(a) Write an ionic equation for the reaction between zinc and hydrochloric acid.

(b) Calculate the number of moles of hydrochloric acid used.

(c) Calculate the volume of hydrogen gas liberated at room conditions.[Molar volume: 24 dm3 mol-1]

2 Excess magnesium carbonate powder, MgCO3, is reacted with 100 cm3 of a 1 mol dm-3 sulphuric acid H2SO4 , What is the mass of magnesium sulphate formed?[Relative atomic mass : Mg =24, O=16, S = 32 ]

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FORM 4 CHEMISTRY CHAPTER 8: SALTS________________________________________________________________________________________________3. 0.12 g of magnesium reacts with excess hydrochloric acid to produce hydrogen gas. [Relative atomic

mass: H, 1; Mg, 24, CI, 35.5. Molar volume: 24 dm3 mol-1 at room conditions] Fnd the (a) mass of salt formed (b) volume of gas produced

4. A sample of insoluble silver chloride is prepared by mixing 50 cm3 of 1.0 mol dm-3 silver nitrate solution and z cm3 of 0.5 mol dm3 sodium chloride solution. [Relative atomic mass: Ag, 108; C,l 35.5]

(a) Write the chemical equation for the reaction between silver nitrate and sodium chloride.

(b) Calculate the volume, z, of the sodium chloride needed to react completely with the silvernitrate solution.

(b) Calculate the mass of silver chloride obtained.

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FORM 4 CHEMISTRY CHAPTER 8: SALTS________________________________________________________________________________________________B. QUALITATIVE ANALYSIS OF SALTS

Learning Outcomes You should be able to:

state the meaning of qualitative analysis make inferences on salts based on their colour and solubility in water describe tests for the identification of gases describe the action of heat on salts describe the tests for anions state observation of reaction of cations with sodium hydroxide solution and ammonia

solution describe confirmatory tests for Fe2+, Fe3+, Pb2+ and NH4

+

Activity 11: Qualitative analysis

1. Qualitative analysis of a salt is a chemical technique used to identify the ……...... that are present in a

salt by analysing its ………………. and ……………………. properties. Physical tests include colour

and solubility in water. Chemical tests include test for gases, test for anions and test for cations.

2. Complete the table below for the physical properties of some common salts.

Salt Colour

Solid Aqueous solutionPotassium saltsSodium saltsAmmonium saltsCalcium saltsLead(II) saltsZinc salts(with colourless anions)

Carbonate saltsChloride saltsNitrate saltsSulphate salts(with colourless anions)

Iron(II) chlorideIron(II) nitrateIron(II) sulphate

Copper(II) chloride Copper(II) nitrateCopper(II) sulphate

Copper(II) carbonate

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Compound Solubility in waterAmmonium saltsSodium and potassium saltsEthanoate saltsNitrate saltsChloride saltsSulphate saltsCarbonate saltsMetal oxidesMetal hydroxides

Activity 12: Confirmatory tests for gases

Complete the observation for the confirmatory test for gases

Gas Method Diagram ObservationCarbon dioxide

Bubble the gas through limewater

Oxygen Insert a glowing wooden splinter into the test tube

Nitrogen dioxide

Bring a piece of moist blue litmus paper to the mouth of the test tube

Chlorine Bring a piece of moist blue litmus paper to the mouth of the test tube

Ammonia Bring a piece of moist red litmus paper to the mouth of the test tube

.

Bring a lighted wooden splinter to the

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Tests for gases


Hydrogen mouth of the test tube

Hydrogen chloride

Use a glass rod to bring a drop of concentrated ammonia solution to the mouth of test tube

Activity 13: Action of heat on carbonate salts

Most carbonate salts (except sodium carbonate and potassium carbonate) decomposes on heating to produce metal oxide and carbon dioxide gas.

Complete the chemical equations and observations for the action of heat on carbonate salt

Carbonate salt Action of heatPotassium carbonate Sodium carbonate

Do not decomposes

Calcium carbonateMagnesium carbonateAluminium carbonateZinc carbonateIron(III) carbonateLead(II) carbonateCopper(II) carbonate

Decomposes to produce metal oxide and carbon dioxide

Example:

…………… …………… + ……………

Observation :

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Metal oxideColourCopper (II) oxideBlackZinc oxideHot: yellow

Cold: WhiteLead (II) oxideHot: brown Cold: yellowIron(III)

oxideBrown

Lime water turn chalky


Silver carbonate Decomposes to produce metal, oxygen and carbon dioxide

Example:

……………. .……….. + ………….. + …………..

Observation:

Ammonium carbonate Decomposes to produce ammonia, water and carbon dioxide

Example:

………….. …………. + …………... + ……………

Observation:

Activity 14: Action of heat on nitrate salts

Activity: Complete the chemical equation and observation for the action of heat on nitrate salt

Nitrate salts Action of heatPotassium nitrate Sodium nitrate

Decomposes to produce a nitrite salt and oxygen

Example:

………… ………..... + ………….

………… ……….. .. + …. ………

Observation:

Calcium nitrateMagnesium nitrateAluminium nitrateZinc nitrateIron(II) nitrateIron(III) nitrateLead(II)nitrateCopper(II) nitrate

Decomposes to produce metal oxide, nitrogen dioxide and oxygen

Example:

…………. …………. + …………… + ……………

Observation:

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Brown gas released turns moist blue litmus to red

Colourless gas released lights up glowing splinter

Heat Heat


Silver nitrate Decomposes to produce metal, nitrogen dioxide and oxygen

Example:

…………. …………. + …………… + ……………

Observation:

Ammonium nitrate Decomposes to produce nitrous oxide and water

Example:

………… ………..... + ………….

Observation:

Activity 15: Confirmatory tests for anions

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Tests for anions


Activity 16: Confirmatory tests for cations (general tests)

1. The presence of cations can be tested using sodium hydroxide solution and ammonia solution. These two alkalis provide hydroxide ions that combine with cations to form metal hydroxides.

2. Except for ammonium ion, most cations will combine with hydroxide ions to form insoluble metal hydroxide (precipitate). The precipitate may or may not be soluble in excess alkali.

3. The colour of the precipitate formed and their solubility in excess alkalis are used to identify the cations.

State whether each of the following precipitate is soluble or insoluble in excess alkali.

Sodium hydroxide solution Ammonia solutionDrop by drop In excess Drop by drop In excess

Soluble ( , X ) Soluble ( , X )Ca2+ White precipitate No changeZn2+ White precipitate White precipitateAl 3+ White precipitate White precipitatePb 2+ White precipitate White precipitateMg2+ White precipitate White precipitateCu 2+ Blue precipitate Blue precipitateFe 2+ Green precipitate Green precipitateFe 3+ Brown precipitate Brown precipitate

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Observe the solubility of precipitate in excess alkali

Drop by drop of alkali(NaOH or NH3)

Solution of cations

Observe the formation of precipitate

Tests for cations

FORM 4 CHEMISTRY CHAPTER 8: SALTS________________________________________________________________________________________________Activity 17: Confirmatory tests for Fe 2+ , Fe 3+ , Pb 2+ and NH 4

+ ions (specific tests)

(A) The table shows below show how confirmatory tests are conducted for ammonium ion, NH4+, iron(II)

ion, Fe2+, iron(III) ion, Fe3+ and lead(II) ion, Pb2+.

Cation Procedure ObservationNH4

+ Method I:

1. About 2 cm3 of ammonium chloride solution is poured into a test tube.

2. About 4 cm3 of dilute sodium hydroxide solution is added to the test tube and the mixture is shaken well.

3. The mixture is carefully heated and the gas liberated is tested with a piece of moist red litmus paper.

Method II:

1. About 2 cm3 of ammonium chloride solution is poured into a test tube.

2. A dropper is used to add Nessler’s reagent drop by drop to the solution.

3. Any change that occurs is noted.

Method I:

The colourless gas released turns red litmus paper blue.

Method II:

A brown precipitate is formed.

Fe2+ 1. About 2 cm3 of iron(II) sulphate solution is poured into a test tube.

2. A dropper is used to add potassium hexacyanoferrate(III) solution, drop by drop into the test tube.

3. Any change that occurs is recorded.

A dark blue precipitate is formed.

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FORM 4 CHEMISTRY CHAPTER 8: SALTS________________________________________________________________________________________________Fe3+ Method I:

1. About 2 cm3 of iron(III) chloride solution is poured into a test tube.

2. A dropper is used to add potassium hexacyanoferrate(II) solution drop by drop into the test tube.

3. Any changes that occurs is recorded.

Method II:

1. About 2 cm3 of iron(III) chloride solution is poured into a test tube.

2. A dropper is used to add potassium thiocyanate solution drop by drop into the test tube.


Method I:

A dark blue precipitate is formed.

Method II:

A blood-red colouration is formed.

Pb2+ Method I:

1. About 2 cm3 of lead(II) nitrate solution is poured into a test tube.

2. A dropper is used to add about 1 cm3 of sodium chloride solution into the test tube.

3. About 3 cm3 of distilled water is added and the mixture is boiled.

4. The mixture is then cooled using running water from the tap.


Method II:

1. About 2 cm3 of lead(II) nitrate is poured into a test tube.

2. A dropper is used to add about 1 cm3

of potassium iodide solution into the test tube.

3. About 3 cm3 of distilled water is added and the mixture is boiled.

4. The mixture is then cooled using running water from the tap.


Method I:

A white precipitate which is soluble in hot water but insoluble in cold water is formed.

Method II:

A yellow precipitate which is soluble in hot water but insoluble in cold water is formed.

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