Quiz 2 of 12

2020 Chemistry WAEC Theory Past Questions

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Question 1

(a)(i). State Faraday’s first law of electrolysis.

Answer: Faraday’s first law of electrolysis states that the mass of a substance/element deposited/liberated/discharged at the electrode is directly proportional to the quantity of electricity that passes through the electrolyte.

(ii). Distinguish between a strong electrolyte and a weak electrolyte.

Answer: A strong electrolyte ionizes or dissociates completely in an aqueous solution. A weak electrolyte ionizes or dissociates only partially in water or aqueous solution.  

 

(b). State one chemical property of ethyne.

Answer: - It combusts or burns in oxygen/air - it undergoes polymerization reaction - it undergoes addition reaction - it undergoes substitution/precipitation reaction  

 

(c)(i). What is meant by the term unsaturated hydrocarbon?

Answer: Unsaturated hydrocarbons are hydrocarbons with at least a double bond or a triple bond or a multiple bond between a pair of carbon atoms in their molecule.

(ii). Complete the following reaction. CH3COOH + CH3OH →

Answer:  CH3COOH + CH3OH CH3COOCH3 + H2O

(iii). Name one major product formed in the reaction in 1(c)(ii).

Answer: Methylethanoate  

 

(d). State one way by which the rate of esterification could be increased.

- addition of concentrated H2SO4

- removal of the ester as soon as it is formed

- increase the concentration of one of the reactants

[Any one ].  

 

(e). Consider the reaction represented by the following equation:

Zn(s) + H2SO4(aq) → ZnSO4(aq) + H2(g)

If 3.75g of Zn dust was added to excess H2SO4(aq), calculate the number of molecules of H2 gas produced.

Answer: From the equation for the reaction,

65g of Zn ≡ 1 mole of H2

65g of Zn ≡ 1 x 6.02 x 1023 of H2

3.75g of Zn  ≡ \( \frac{3.75 \: \times \: 6.02 \: \times \: 10^{23}}{65} \)

= 3.47 x 1022 molecules of H2  

 

(f). State one effect of global warming.

Answer:

- severe climate change

- sea level rising

- flooding of low-lying areas

- severe drought

- depletion of coral reefs

- melting of ice at the polar regions

- Disturbing the balance of the ecosystem  

[Any one].

 

(g). Consider the following reaction equations

A. Pb(NO3)2 + H2S   → PbS + 2HNO3;

B. H2 + C2H4  → C2H6

C. Zn(OH)2 + 2OH-  → Zn(OH)4]2-

(i). Which of the equations represent(s) redox process?

Answer: Equation B:  H2 + C2H4  → C2H6

(ii). State the change in oxidation number of the species that are oxidized or reduced.

Answer: The oxidation state of

 

(h) (i). State two main concepts of Bohr’s model of an atom.

Answer:

- an electron in an atom revolves around the nucleus in a circular orbit

- each electron posses a discrete energy/energy of an electron is quantized

- movement of an electron from a higher energy level to a lower energy level leads to the emission of energy

[Any two]

(ii). State the limitation of the model.

Answer: - The model cannot explain more complicated spectral lines other than the simple spectral lines observed in hydrogen - The model also assumes that electrons possess known position and momentum at the same time which is in violation of Heisenberg Uncertainty Principle.  

 

(i). List three factors that could influence the equilibrium position of a reversible reaction.

Answer: - pressure/volume - concentration - temperature  

 

(j). Calcium trioxocarbonate (IV) powder was added to equimolar solutions of hydrochloric acid. State one:

(i). similarity in the observation in both reactions

Answer: Effervescence/gas is given off

(ii).difference in the observation in both reactions.

Answer: Reaction involving HCl will be more vigorous (HCl is a strong acid). The reaction involving ethanoic acid will be less vigorous (ethanoic acid is a weak acid).

Question 2

(a). Consider the following compounds.

(i). What is the relationship between the compounds label A and B?

Answer: They are geometric isomers/cis-trans isomers

(ii). Name each of the compounds A and B.

Answer:

A is trans-1,2-dichloroethane

B is cis-1,2-dichloroethane

(iii). Will the chemical compound of A and B be the same?

Answer: Yes/ Their chemical properties will be the same.

(iv). Give the reason for the answer in 2(a) (iii).

Answer:

- They have the same functional group

- They possess the same atoms arranged in the same way

 

(b)(i). Give two characteristics features of boiling.

Answer:

- boiling occurs at a specific temperature

- boiling occurs throughout the liquid

- bubbles are formed during boiling which rises to the surface

- Liquid particles change to vapour when the pressure of the liquid equals atmospheric pressure

[Any two]

(ii). What will be the effect of each of the following conditions on the boiling point of water?

(I) Addition of crystals of sodium chloride.

Answer: increases the boiling point of water

(II) Reduction of the atmospheric pressure.

Answer:  lowers the boiling point of water

(iii). State one way in which boiling differs from evaporation.

Answer:

Boiling Evaporation
Occurs at a specific temperature Occurs at all temperatures
Occurs throughout the liquid Occurs only at the surface of the liquid
Does not cause cooling Cause cooling
Caused by an external source of energy/not spontaneous Caused by internal energy/spontaneous
Bubbles are observed No bubbles observed
Not affected by humidity Affected by humidity
It releases heat to the surrounding It absorbs heat from the surrounding

[Any one]

 

(c)(i). Differentiate between an unsaturated solution and a saturated solution.

Answer:

Unsaturated solution Saturated solution
Can dissolve more solute at that temperature Cannot dissolve more solute at that temperature
Does not contain undissolved solute at that temperature Contains dissolve solute at that temperature

(ii). State two ways by which a saturated solution could be made to dissolve more solute.

Answer:

- increasing the temperature of the solution

- Increasing the volume of the solvent

(iii). State one factor that could affect the solubility of a solid in a liquid.

Answer:

- temperature

- nature of the solvent

- volume of solvent

- nature of the solute

[Any one]

 

(d)(i). Define the term mole.

A mole is the amount of substance which contains Avogadro’s number/6.02x1023 particles of that substance. OR

A mole is the amount of substance containing as many particles as are there in 12g of carbon-12.

 

(ii). Consider the following reaction equation:

Mgo(s) + 2HCl(aq) → MgCl2(aq) + H2O(l)

Find the Mass of MgO

Answer:

moles of HCl, n = cv

n = \( \frac{25\: \times \: 0.1}{1000} \)

= 0.025miles

From the equation for the reaction mole of MgO to HCl = 1:2

Molar mass of MgO = 24 + 16 = 40g/mol

Mass of MgO = ½ x 0.0025 x 40

= 0.050g

 

(e). State three physical properties of metals.

Answer:

- Except mercury (which is liquid) all metals are solids at room temperature.

- Metals are lustrous

- Metals are malleable. They can be hammered into thin sheets

- Metals are ductile

- All metals are hard (except sodium and potassium) but not brittle

- Metals are good conductors of heat and electricity

- Metals have high density and are very heavy

- Metals have high melting and boiling points

- Metals are sonorous

[Any three]

Question 3

(a). In an equilibrium reaction between gases Q2 and R2 to form QR, the energy content of the reactants is 100kJ and that of the product is 54kJ. The energy content of the activated complex is 210 kJ.

(i). Draw an energy profile diagram for the reaction.

(ii). Determine the:

I. Activation energy of the reaction;

Answer: Activation energy = 210 – 100 = 110 kJ

II. Enthalpy change  ΔH of the reaction.

Answer:

ΔH = Hp - Hr

 = 54 – 100 = -46kJ/mol

 

(iii). Write a balanced equation for the reaction.

Answer: Q2(g) – R2(g) ⇌  2QR(g)

(iv). State whether the reaction is exothermic or endothermic.

Answer: The reaction is an exothermic reaction.

(v). Give a reason for the answer in 3(a)(iv).

Answer:

The enthalpy change ΔH is negative/the reaction liberated heat to the environment/the energy of the reactant is higher than the energy of the product.

 

(b). Consider the following table:

Element E F G H
Atomic number 7 9 12 13

 

(i). Write the electronic configuration for each element.

Answer:

E – 1s2 2s2 2p3

F – 1s2 2s2 2p5

G – 1s2 2s2 2p6 3S2

H – 1s2 2s2 2p6 3S2 3P1

(ii). State

(I) two elements that are metals.

Answer: Elements H and G

(II) The element(s) most likely to form ions with a charge of +3.

Answer: Element H

(III) the element(s) which belong to group (VII) on the periodic table;

Answer: Element F

(IV)the formula of the compound formed between F and G.

Answer: Element GF2

 

(c). Define the term isotopy.

Answer:  Isotopy is the existence of atoms of the same element with the same atomic number but a different mass number or nucleon number or number of neutrons.

OR

Isotopy is the phenomenon where atoms of the same element have the same atomic number but a different mass number or nucleon number or number of neutrons.

 

(d). Name the three building blocks of matter.

Answer:  Atoms, Ions, and Molecules

FOR CANDIDATES IN NIGERIA AND THE GAMBIA

Question 4

(a)(i). in the laboratory preparation of dry chlorine gas, state the:

(I) reagent used.

Answer: Conc. HCl and KMnO4 or MnO2 i.e. concentrated hydrochloric acid and potassium tetraoxomanganate (VII) or manganese (IV) oxide

(II) drying agent used;

Answer: Conc. Tetraoxosulphate (VI) acid or Conc. H2SO4

(III) the mode of collection.

Answer: Upward displacement of air i.e. downward delivery

 

(ii). Write the equation for the preparation of chlorine.

Answer:

16HCl(aq) + 2KMnO4(aq) → 2MnCl2(aq) + 2KCl(aq) + 8H2O(l) + 5Cl2(g)

OR

MnO2 + 4HCl → MnCl2(aq) + NaClO3(aq) + 3H2O(l)

(iii). Write an equation to show how chlorine reacts with hot concentrated NaOH.  

Answer: 3Cl2(g) + 6NaOH(aq)  →  5NaCl(aq) + NaClO3(aq) + 3H2O(l)

 

(b)(i). Name the main raw materials used for the extraction of iron in the blast furnace.

Answer: Haematite; Limestone and Coke

(ii). Write the equation of the reaction taking place in the blast furnace.

Answer:

C(s) + O2(g) →  CO2(g)

C(s) + CO2(g) → 2CO(g)

Fe2O3 + 3CO ⇌  2Fe + 3CO2

CaCO3 →  CaO + CO2

CaO + SiO2 →  CaSiO3

(iii). What is the name given to iron obtained directly from the blast furnace?

Answer: Pig iron

(iv). State why the iron named in 4(b)(iii) has a relatively low melting point.  

Answer: Because of the presence of impurities in it.

 

(c). The following equation represents one of the steps involved in the contact process.

2SO2(g) + O2(g)  → 2SO3(g)   H = -395.7kJmol-1

(i). Why is the SO3 produced during the reaction not dissolve directly in water to form H2SO4?

Answer: The dissolution of SO3 in water is highly exothermic. This dissolution produces a mist of acid droplets.

(ii). Why is H2SO4 regarded as a heavy chemical?

Answer:

- H2SO4 is produced on a large scale

- H2SO4 is used as raw material in many industrial processes

- H2SO4 is in high demand by industries

(iii). State the property exhibited by tetraoxosulphate (VI) acid in each of the following reaction equations.

(I) Pb(NO3)2 + H2SO4(aq) → PbSO4(s) + HNO3(aq)

Answer: Displacement/precipitating agent

(II) H2S(g) + H2SO4(aq) → S(s) + 2H2O(l) + SO2(g)

Answer: Oxidizing agent

(d) Write a balanced chemical equation for the reaction between propanol and sodium.

Answer:

2CH3CH2CH2OH + 2Na →  2CH3CH2CH2ONa + H2

OR

2C3H7OH + 2Na  →   2C3H7ONa + H2

Question 5

(a)(i). Name two gases that can be used to perform the fountain experiment.

Answer:

-ammonia

- hydrogen chloride

- sulphur (IV) oxide

[Any two]

(ii). What is the aim of the experiment?

Answer: To demonstrate the extreme/high solubility of NH3/HCl/SO2 in water.

(iii). Describe briefly, the fountain experiment.

Answer: A flask fitted with a glass jet is filled with NH3 gas or HCl gas or SO2 gas. Water is injected through the inlet of the flask. The water dissolves the gas and causes a fountain through the jet.

 

(b)(i). Name two chemical industries.

Answer:

- Paint 

- Textiles

- Fertilizers

- Plastic

- Pharmaceuticals

- Petrochemical industry

[Any two of the above]

(ii). State three effects of the chemical industry on the community in which it is sited.

Answer:

- An improved standard of living

- Development of the community

- Job opportunities

- Pollution of land, air, water, etc.

[Any three]

 

(c)(i). Name three products of the destructive distillation of coal.

Answer:

- coke

- coal tar

- coal gas

- ammoniacal liquor

[Any three]

(ii). Give one use each of any two of the products named in 5(c)(i).

Answer:

- Coke is used in fuel/production of water gas/extraction of metals

- Coal tar is used in the synthesis of chemicals/perfumes/dyes/paints/drugs/plastics/explosives/tarring of roads

- Coal gas is used as fuel in homes and industries

- Ammoniacal liquor is used in the production of fertilizer

[Any two].

 

(d)(i). Name two substances responsible for the hardness in water.

Answer:

- calcium hydrogen trioxocarbonate (IV)

- magnesium hydrogen trioxocarbonate (IV)

- calcium tetraoxosulphate (VI)

- magnesium tetraoxosulphate (VI)

- iron (III) chloride

[Any two]

(ii). State two methods of the removal of hardness in water.

Answer:

-    boiling/distillation

[Any two].

(iii). State two advantages of hard water.

Answer:

- calcium ions in the water are good for children’s teeth and bones

-  It helps to reduce heart diseases

-  Does not dissolve lead pipes

 - Tastes better than soft water

-  Provides calcium salts used in the manufacturing of food in plants

-  Production of the exoskeleton of animals/shells

[Any two].

Question 1

(a)(i). State Faraday’s first law of electrolysis.

Answer: Faraday’s first law of electrolysis states that the mass of a substance/element deposited/liberated/discharged at the electrode is directly proportional to the quantity of electricity that passes through the electrolyte.

(ii). Distinguish between a strong electrolyte and a weak electrolyte.

Answer: A strong electrolyte ionizes or dissociates completely in an aqueous solution. A weak electrolyte ionizes or dissociates only partially in water or aqueous solution.  

 

(b). State one chemical property of ethyne.

Answer: - It combusts or burns in oxygen/air - it undergoes polymerization reaction - it undergoes addition reaction - it undergoes substitution/precipitation reaction  

 

(c)(i). What is meant by the term unsaturated hydrocarbon?

Answer: Unsaturated hydrocarbons are hydrocarbons with at least a double bond or a triple bond or a multiple bond between a pair of carbon atoms in their molecule.

(ii). Complete the following reaction. CH3COOH + CH3OH →

Answer:  CH3COOH + CH3OH CH3COOCH3 + H2O

(iii). Name one major product formed in the reaction in 1(c)(ii).

Answer: Methylethanoate  

 

(d). State one way by which the rate of esterification could be increased.

- addition of concentrated H2SO4

- removal of the ester as soon as it is formed

- increase the concentration of one of the reactants

[Any one ].  

 

(e). Consider the reaction represented by the following equation:

Zn(s) + H2SO4(aq) → ZnSO4(aq) + H2(g)

If 3.75g of Zn dust was added to excess H2SO4(aq), calculate the number of molecules of H2 gas produced.

Answer: From the equation for the reaction,

65g of Zn ≡ 1 mole of H2

65g of Zn ≡ 1 x 6.02 x 1023 of H2

3.75g of Zn  ≡ \( \frac{3.75 \: \times \: 6.02 \: \times \: 10^{23}}{65} \)

= 3.47 x 1022 molecules of H2  

 

(f). State one effect of global warming.

Answer:

- severe climate change

- sea level rising

- flooding of low-lying areas

- severe drought

- depletion of coral reefs

- melting of ice at the polar regions

- Disturbing the balance of the ecosystem  

[Any one].

 

(g). Consider the following reaction equations

A. Pb(NO3)2 + H2S   → PbS + 2HNO3;

B. H2 + C2H4  → C2H6

C. Zn(OH)2 + 2OH-  → Zn(OH)4]2-

(i). Which of the equations represent(s) redox process?

Answer: Equation B:  H2 + C2H4  → C2H6

(ii). State the change in oxidation number of the species that are oxidized or reduced.

Answer: The oxidation state of

 

(h) (i). State two main concepts of Bohr’s model of an atom.

Answer:

- an electron in an atom revolves around the nucleus in a circular orbit

- each electron posses a discrete energy/energy of an electron is quantized

- movement of an electron from a higher energy level to a lower energy level leads to the emission of energy

[Any two]

(ii). State the limitation of the model.

Answer: - The model cannot explain more complicated spectral lines other than the simple spectral lines observed in hydrogen - The model also assumes that electrons possess known position and momentum at the same time which is in violation of Heisenberg Uncertainty Principle.  

 

(i). List three factors that could influence the equilibrium position of a reversible reaction.

Answer: - pressure/volume - concentration - temperature  

 

(j). Calcium trioxocarbonate (IV) powder was added to equimolar solutions of hydrochloric acid. State one:

(i). similarity in the observation in both reactions

Answer: Effervescence/gas is given off

(ii).difference in the observation in both reactions.

Answer: Reaction involving HCl will be more vigorous (HCl is a strong acid). The reaction involving ethanoic acid will be less vigorous (ethanoic acid is a weak acid).

Question 2

(a). Consider the following compounds.

(i). What is the relationship between the compounds label A and B?

Answer: They are geometric isomers/cis-trans isomers

(ii). Name each of the compounds A and B.

Answer:

A is trans-1,2-dichloroethane

B is cis-1,2-dichloroethane

(iii). Will the chemical compound of A and B be the same?

Answer: Yes/ Their chemical properties will be the same.

(iv). Give the reason for the answer in 2(a) (iii).

Answer:

- They have the same functional group

- They possess the same atoms arranged in the same way

 

(b)(i). Give two characteristics features of boiling.

Answer:

- boiling occurs at a specific temperature

- boiling occurs throughout the liquid

- bubbles are formed during boiling which rises to the surface

- Liquid particles change to vapour when the pressure of the liquid equals atmospheric pressure

[Any two]

(ii). What will be the effect of each of the following conditions on the boiling point of water?

(I) Addition of crystals of sodium chloride.

Answer: increases the boiling point of water

(II) Reduction of the atmospheric pressure.

Answer:  lowers the boiling point of water

(iii). State one way in which boiling differs from evaporation.

Answer:

Boiling Evaporation
Occurs at a specific temperature Occurs at all temperatures
Occurs throughout the liquid Occurs only at the surface of the liquid
Does not cause cooling Cause cooling
Caused by an external source of energy/not spontaneous Caused by internal energy/spontaneous
Bubbles are observed No bubbles observed
Not affected by humidity Affected by humidity
It releases heat to the surrounding It absorbs heat from the surrounding

[Any one]

 

(c)(i). Differentiate between an unsaturated solution and a saturated solution.

Answer:

Unsaturated solution Saturated solution
Can dissolve more solute at that temperature Cannot dissolve more solute at that temperature
Does not contain undissolved solute at that temperature Contains dissolve solute at that temperature

(ii). State two ways by which a saturated solution could be made to dissolve more solute.

Answer:

- increasing the temperature of the solution

- Increasing the volume of the solvent

(iii). State one factor that could affect the solubility of a solid in a liquid.

Answer:

- temperature

- nature of the solvent

- volume of solvent

- nature of the solute

[Any one]

 

(d)(i). Define the term mole.

A mole is the amount of substance which contains Avogadro’s number/6.02x1023 particles of that substance. OR

A mole is the amount of substance containing as many particles as are there in 12g of carbon-12.

 

(ii). Consider the following reaction equation:

Mgo(s) + 2HCl(aq) → MgCl2(aq) + H2O(l)

Find the Mass of MgO

Answer:

moles of HCl, n = cv

n = \( \frac{25\: \times \: 0.1}{1000} \)

= 0.025miles

From the equation for the reaction mole of MgO to HCl = 1:2

Molar mass of MgO = 24 + 16 = 40g/mol

Mass of MgO = ½ x 0.0025 x 40

= 0.050g

 

(e). State three physical properties of metals.

Answer:

- Except mercury (which is liquid) all metals are solids at room temperature.

- Metals are lustrous

- Metals are malleable. They can be hammered into thin sheets

- Metals are ductile

- All metals are hard (except sodium and potassium) but not brittle

- Metals are good conductors of heat and electricity

- Metals have high density and are very heavy

- Metals have high melting and boiling points

- Metals are sonorous

[Any three]

Question 3

(a). In an equilibrium reaction between gases Q2 and R2 to form QR, the energy content of the reactants is 100kJ and that of the product is 54kJ. The energy content of the activated complex is 210 kJ.

(i). Draw an energy profile diagram for the reaction.

(ii). Determine the:

I. Activation energy of the reaction;

Answer: Activation energy = 210 – 100 = 110 kJ

II. Enthalpy change  ΔH of the reaction.

Answer:

ΔH = Hp - Hr

 = 54 – 100 = -46kJ/mol

 

(iii). Write a balanced equation for the reaction.

Answer: Q2(g) – R2(g) ⇌  2QR(g)

(iv). State whether the reaction is exothermic or endothermic.

Answer: The reaction is an exothermic reaction.

(v). Give a reason for the answer in 3(a)(iv).

Answer:

The enthalpy change ΔH is negative/the reaction liberated heat to the environment/the energy of the reactant is higher than the energy of the product.

 

(b). Consider the following table:

Element E F G H
Atomic number 7 9 12 13

 

(i). Write the electronic configuration for each element.

Answer:

E – 1s2 2s2 2p3

F – 1s2 2s2 2p5

G – 1s2 2s2 2p6 3S2

H – 1s2 2s2 2p6 3S2 3P1

(ii). State

(I) two elements that are metals.

Answer: Elements H and G

(II) The element(s) most likely to form ions with a charge of +3.

Answer: Element H

(III) the element(s) which belong to group (VII) on the periodic table;

Answer: Element F

(IV)the formula of the compound formed between F and G.

Answer: Element GF2

 

(c). Define the term isotopy.

Answer:  Isotopy is the existence of atoms of the same element with the same atomic number but a different mass number or nucleon number or number of neutrons.

OR

Isotopy is the phenomenon where atoms of the same element have the same atomic number but a different mass number or nucleon number or number of neutrons.

 

(d). Name the three building blocks of matter.

Answer:  Atoms, Ions, and Molecules

FOR CANDIDATES IN NIGERIA AND THE GAMBIA

Question 4

(a)(i). in the laboratory preparation of dry chlorine gas, state the:

(I) reagent used.

Answer: Conc. HCl and KMnO4 or MnO2 i.e. concentrated hydrochloric acid and potassium tetraoxomanganate (VII) or manganese (IV) oxide

(II) drying agent used;

Answer: Conc. Tetraoxosulphate (VI) acid or Conc. H2SO4

(III) the mode of collection.

Answer: Upward displacement of air i.e. downward delivery

 

(ii). Write the equation for the preparation of chlorine.

Answer:

16HCl(aq) + 2KMnO4(aq) → 2MnCl2(aq) + 2KCl(aq) + 8H2O(l) + 5Cl2(g)

OR

MnO2 + 4HCl → MnCl2(aq) + NaClO3(aq) + 3H2O(l)

(iii). Write an equation to show how chlorine reacts with hot concentrated NaOH.  

Answer: 3Cl2(g) + 6NaOH(aq)  →  5NaCl(aq) + NaClO3(aq) + 3H2O(l)

 

(b)(i). Name the main raw materials used for the extraction of iron in the blast furnace.

Answer: Haematite; Limestone and Coke

(ii). Write the equation of the reaction taking place in the blast furnace.

Answer:

C(s) + O2(g) →  CO2(g)

C(s) + CO2(g) → 2CO(g)

Fe2O3 + 3CO ⇌  2Fe + 3CO2

CaCO3 →  CaO + CO2

CaO + SiO2 →  CaSiO3

(iii). What is the name given to iron obtained directly from the blast furnace?

Answer: Pig iron

(iv). State why the iron named in 4(b)(iii) has a relatively low melting point.  

Answer: Because of the presence of impurities in it.

 

(c). The following equation represents one of the steps involved in the contact process.

2SO2(g) + O2(g)  → 2SO3(g)   H = -395.7kJmol-1

(i). Why is the SO3 produced during the reaction not dissolve directly in water to form H2SO4?

Answer: The dissolution of SO3 in water is highly exothermic. This dissolution produces a mist of acid droplets.

(ii). Why is H2SO4 regarded as a heavy chemical?

Answer:

- H2SO4 is produced on a large scale

- H2SO4 is used as raw material in many industrial processes

- H2SO4 is in high demand by industries

(iii). State the property exhibited by tetraoxosulphate (VI) acid in each of the following reaction equations.

(I) Pb(NO3)2 + H2SO4(aq) → PbSO4(s) + HNO3(aq)

Answer: Displacement/precipitating agent

(II) H2S(g) + H2SO4(aq) → S(s) + 2H2O(l) + SO2(g)

Answer: Oxidizing agent

(d) Write a balanced chemical equation for the reaction between propanol and sodium.

Answer:

2CH3CH2CH2OH + 2Na →  2CH3CH2CH2ONa + H2

OR

2C3H7OH + 2Na  →   2C3H7ONa + H2

Question 5

(a)(i). Name two gases that can be used to perform the fountain experiment.

Answer:

-ammonia

- hydrogen chloride

- sulphur (IV) oxide

[Any two]

(ii). What is the aim of the experiment?

Answer: To demonstrate the extreme/high solubility of NH3/HCl/SO2 in water.

(iii). Describe briefly, the fountain experiment.

Answer: A flask fitted with a glass jet is filled with NH3 gas or HCl gas or SO2 gas. Water is injected through the inlet of the flask. The water dissolves the gas and causes a fountain through the jet.

 

(b)(i). Name two chemical industries.

Answer:

- Paint 

- Textiles

- Fertilizers

- Plastic

- Pharmaceuticals

- Petrochemical industry

[Any two of the above]

(ii). State three effects of the chemical industry on the community in which it is sited.

Answer:

- An improved standard of living

- Development of the community

- Job opportunities

- Pollution of land, air, water, etc.

[Any three]

 

(c)(i). Name three products of the destructive distillation of coal.

Answer:

- coke

- coal tar

- coal gas

- ammoniacal liquor

[Any three]

(ii). Give one use each of any two of the products named in 5(c)(i).

Answer:

- Coke is used in fuel/production of water gas/extraction of metals

- Coal tar is used in the synthesis of chemicals/perfumes/dyes/paints/drugs/plastics/explosives/tarring of roads

- Coal gas is used as fuel in homes and industries

- Ammoniacal liquor is used in the production of fertilizer

[Any two].

 

(d)(i). Name two substances responsible for the hardness in water.

Answer:

- calcium hydrogen trioxocarbonate (IV)

- magnesium hydrogen trioxocarbonate (IV)

- calcium tetraoxosulphate (VI)

- magnesium tetraoxosulphate (VI)

- iron (III) chloride

[Any two]

(ii). State two methods of the removal of hardness in water.

Answer:

-    boiling/distillation

[Any two].

(iii). State two advantages of hard water.

Answer:

- calcium ions in the water are good for children’s teeth and bones

-  It helps to reduce heart diseases

-  Does not dissolve lead pipes

 - Tastes better than soft water

-  Provides calcium salts used in the manufacturing of food in plants

-  Production of the exoskeleton of animals/shells

[Any two].