Quiz 8 of 12

2016 Chemistry WAEC Theory Past Questions

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Question 1

(a) What are nucleons?

Answer: Nucleons refer to protons and neutrons. They are found in the nucleus of an atom. They are nuclear particles which are protons and neutrons.

 

(b) State Graham's law of diffusion.

Answer: Graham’s law of diffusion states that, at constant temperature and pressure, the rate of diffusion of a gas is inversely proportional to the square root of its density.

Mathematically, \( \scriptsize r \propto  \normalsize \frac{1}{\sqrt{d}} \)

 

(c) Explain briefly why aluminium does not corrode easily.

Answer: Aluminium oxide layer forms on the surface of the metal. The oxide layer forms a protective coating. This coating prevents aluminium from further attack. It is impermeable to water or air.

 

(d) State three examples of periodic properties.

Answer: 

 

(e) State two reasons why real gases deviate from ideal gas behaviour.

Answer: 

 

(f) List three uses of fractional distillation in industry.

Answer: 

 

(g) What factors determine the selective discharge of ions at the electrodes during electrolysis?

Answer: 

  1. The position of the ions in the electrochemical series
  2. Concentration of the ion in the electrolyte
  3. Nature of the electrodes used.

 

(h) State the type of reaction represented by each of the following equations:

i. C2H2  +  Br2 →  C2H5Br  +  Br

Answer: Substitution reaction

ii. C2H4   +  Br2 →  C2H4Br2

Answer: Addition reaction

 

(i) Name the products formed when butane burns in a limited supply of air.

Answer:

 

(j) List three methods of separating a solid from a liquid.

Answer:

  1. Filtraton
  2. Crystallization
  3. Evapoartion
  4. Decantation

Question 2

a) Consider the following atoms: \(\scriptsize ^R_T X\: ;\: ^S_TX\)

(i) State the phenomenon exhibited by the two atoms.

Answer: Isotopy

(ii) What is the difference between the atoms?

Answer: They have different mass numbers due to the difference in the number of neutrons

(iii) Give two examples of elements that exhibit the phenomenon stated in (ai)

Answer:

(iv) lf T is 17, write the electron configuration of the element

Answer: \( \scriptsize _{17} X = 2, \:8,\:7 \)

= 1S22S22P63S23P5

 

(b)(i) State two differences between metals and non-metals with respect to their:

I. Physical properties

Answer: 

Metals

Non – metals

Good conductor of heat and electricity

Poor conductor of heat and electricity

Malleable {can be beaten into sheets}

Non – malleable

Solid at room temperature except for mercury

Solid, liquid, or gaseous at room temperature

High meting point

Low melting point

 

II. Chemical properties.

Answer: 

Metals

Non – metals

Lose their valence electrons easily

Gain or share their valence electrons easily

Form oxides that are bases

Form oxides that are acidic neutral

Are good reducing agents

Are good oxidizing agents

Have lower electronegativity

Have higher electronegativity

Have low ionization energy

Have high ionization energy

(ii) Give one example of each for the following compounds:

I. An amphoteric oxide;

II. A hydride which evolves hydrogen when reacted with water;

Ill. A trioxocarbonate (IV) salt which is readily decomposed on heating;

IV. A chloride salt which is readily hydrolyzed in water.

Answer: 

I. Amphoteric oxides are: Al2O3; ZnO; PbO; BeO

II. Hydrides which evolve hydrogen when reacted with water are: CaCO3; MgH2; KH; LiH

III. Trioxocarbonate (iv) salts which are readily decomposed on heating are: Li2CO3; BeCO3; MgCO3; CaCO3; ZnCO3; PbCO3

IV. Carbonate salts which are readily hydrolyzed in water are: NH4Cl; AlCl3; MgCl2; SiCl4

 

(c)(i) State three characteristic properties of transition metals.

Answer:

(ii) Write the electron configuration of \(\scriptsize _{30}Zn\)

Answer: 30Zn ; 1S22S22P63S23P63d104S2

(iii.) Explain briefly why zinc is not considered as a typical transition element.

Answer: Zinc has a completely filled 3rd orbital and therefore does not have unpaired d-orbital and cannot have variable oxidation state.

 

(d) Consider the reaction represented by the following equation:-

Na2CO3(aq)  +  MgCl2(aq) → NaCl(aq)  +  MgCO3(aq)

Calculate the mass of sodium trioxocarbonate (IV) needed to produce 3.36 of magnesium trioxocarbonate (IV). [C = 12.0, O = 16.0, Na = 23.0, Mg = 24:0 ]

Solution

Na2CO3(aq)  +  MgCl2(aq) → NaCl(aq)  +  MgCO3(aq)

Na2CO3  =  (2 x 23)  +  (12)  +  (3 x 16)  = 106

MgCO3  = (24)  +  (12)  +  (16 x 3)  = 84

From the equation

84g of MgCO3 was produced from 106g NaCO3

    3.36g of MgCO3 will be produced from xg NaCO3

84g is to 106g

as 

3.36 is to xg

\( \frac{84}{106} = \frac{3.36}{x} \)

x = \( \frac{106 \: \times \: 3.36}{84} \)

= 4.24g

Question 3

(a)  (i) Define structural isomerism

Answer: Structural isomerism is the existence/occurrence of two or

(ii) State the class of alkanols to which each of the following compounds belongs:

I. CH3C(CH3)2OH

II. CH3CH(CH3)CH2OH

III. CH3CH2(CH3)OH

Answer:

 

(b) (i) Write the formulae of the products formed in the following reactions:

I. CH3CH2COOH \( \overset{K_{(s)}}{\normalsize \rightarrow}\:  \) CH3CH2COOK  +  H2

II. CH3CH2COOH \( \underset{Con.\: H_2SO_4}{\overset{C_4H_2OH,\: heat}{\normalsize \rightarrow}} \) CH3CH2COOC4H9  +  H2O

III. CH3CH2CH2CH2OH \( \underset{excess}{\overset{H^+\: KMnO_4}{\normalsize \rightarrow}} \)  CH2CH2CH2COOH  +  H2O

(ii) Name the major product(s) of each of the reactions in (b)(i).

*Potassium propanoate

*Butyl propanoate

*Butanoic acid

 

(c) A gaseous hydrocarbon R of mass 7.0g occupies a volume of 2.24dm3 at s.t.p. If the percentage composition by mass of hydrogen is 14.3, determine its

(i) empirical formula;

(ii) molecular formula.

[ H = 1.00, C = 12.0, Molar volume of gas at s.t.p, = 22.4 dm\(_2\)

Solution

Given: Gas R; mass of gass 7.0g; volume of gas = 2.24dm3 at s.t.p

Mass percentage of hydrogen = 14.3%

Find: Empirical formula, Molecular formula!

(I) Empirical formular

%  of carbon by mass = 100 - 14.3 = 85.7%

  C H
% composition 85.7 14.3
Number of atoms 12 1
Ration of atoms \( \frac{85.7}{12}\) \( \frac{14.3}{1}\)
  = 7.1415 =14.3
Divide by smaller Number \( \frac{7.1415}{7.1415}\) \( \frac{14.3}{7.1415}\)
  = 1 = 2

Empirical formular = CH2

II Molecular formular

2.24dm3 has a mass of 7.0g

22.4dm3 would have a mass of xg

x = \( \frac{22.4 \: \times \: 7}{2.24} \)

= 70g

(CH2)n  = 70

{(12) + (1 x 2)n} = 70

(12 + 2)n = 70

14n = 70

n = \( \frac{70}{14} \)

n = 5

molecular formular (CH2)n

= (CH2)5 = C5H10

 

(d) Draw the structures of the isomers of the alkene with molecular formula C4H8

Question 4

(a)(i) Name a suitable drying agent for the preparation of carbon (IV) oxide in the laboratory.

Answer:

(ii) Using one chemical test, distinguish between carbon (II) oxide and carbon (IV) oxide.

Answer: Pass/bubble each gas into lime water. If lime water turns milky, then CO2 is present. If no reaction, then CO is the gas present.

 

(b)(i) Describe briefly how oxygen and nitrogen could be obtained separately from air on an industrial scale

Answer:

(ii) State how a lighted splint can be used to distinguish between samples of oxygen and nitrogen.

Answer: 

 

(c)(i) Give one reason why bauxite is usually preferred as the ore for the extraction of aluminium.

Answer:

(ii). List two main impurities. usually present in bauxite.

Answer: 

(iii) State the function of sodium hydroxide solution in the extraction of aluminium from its ore.

Answer: To dissolve the aluminium so that the impurities can be filtered off.

(iv) Explain briefly why it is difficult to extract aluminium by chemical reduction of aluminium oxide

Answer: Aluminium is very reactive to be reduced by the commonly known reducing agents during extraction due to very strong electrovalent bonding

(v) Write an equation for the reaction of aluminium oxide with aqueous sodium hydroxide.

Answer:

Al2O3  +  2NaOH →  NaAlO2 + H2O

or

Al2O3  +  2NaOH  +  3H2O   →   2NaA(OH)4

 

(d) (i)The melting and boiling points of sodium chloride are 801C and 1413°C, respectively. Explain briefly why sodium chloride does not conduct electricity at 25°C but does so at 801°C and 1413°C.

Answer:  At 25°C, solid (state) sodium chloride ions are not free. Between 801°C and 1413°C, liquid sodium chloride ions are free.     

(ii) State the reason why sodium metal is stored under paraffin oil in the laboratory.

Answer: Sodium metal reacts quickly with moisture and carbon (iv) oxide when exposed.

 

(e)(i) State what would be observed when aqueous sodium trioxocarbonate(IV) is added to a solution containing iron (III) ions

Answer: 

(ii) Write a balanced equation for the reaction in (e)(i).

Answer: 

3Na2CO3(aq)  +  2Fe3+ → Fe2(CO3)3(g)  +  6Na+(aq) 

Question 5

(a)(i) Determine the oxidation number of sulphur in Na2S2O3

Answer: Na2S2O3 = O

2(+1)  +  2(S)  +  3(-2)  = 0

2S  = 6 – 2 = 4

S = +2

(ii) Name the allotropes of sulphur.

Answer:

(iii) State two ways in which the structure of graphite and diamond are similar.

Answer:

 

(b)(i) Name two greenhouse gases.

Answer: 

 

(ii) State one effect of an increased level of greenhouse gases on the environment.

Answer: Global warming/climate change

(iii) State one source from which nitrogen (I) oxide is released into the environment.

Answer: 

(iv) Write a chemical equation to show the effect of heat on each of the following compounds:

(I) KNO3(s)

Answer: 

KNO3(S) \(\overset{heat}{ \rightarrow} \)2KNO2(S)  +  O2(g)

(II) AgNO3(s)

Answer: 

AgNO3(S) \(\overset{heat}{ \rightarrow} \) 2Ag(s)  +  NO2(g)  + O2(g)

 

(c)(i)Describe briefly how pure crystals of calcium chloride could be obtained from a solution of calcium chloride

Answer: By heating the solution to concentrate it. Leave in a warm place. Partially evaporate solution and allow to cool. Filter crystals. Pick out crystals. Dry with filter paper.

(ii) Explain briefly each of the following observations:

I. Ammonia gas is highly soluble in water;

Answer: Ammonia readily associates with water molecules through hydrogen bonding.

II. Boiling point of chlorine is lower than that of iodine

Answer: Chlorine molecules are smaller

 

(d) Consider the reaction represented by the following equation:- 

2NaCl(s)  + H2SO4(aq) → Na2SO4(aq) + 2HCl(g)

Calculate the volume of HCl gas that can be obtained at s.t.p. from 5.85 g of sodium. chloride.

[Na = 23.0; Cl = 35.5; molar volume of gas at s.t.p. = 22.4dm3]

Solution:

Given: mass of NaCl = 5.85g, s.t.p,

NaCl = 23.0 + 35.5 = 58.5g

HCl = 1 + 35.5 = 36.5

According to the equation

2NaCl = 2 x 58.5g of NaCl equivalent 2 x 36.5g of HCl

5.85g of NaCl equivalent x g of HCl

x = \( \frac{2 \: \times \: 36.5 \: \times \: 5.85 }{2 \: \times \: 58.5} \)

x = 3.65g

∴ Volume at s.t.p = \( \frac{3.65 }{36.5} \scriptsize \: \times \: 22.4 \)

= 2.24dm3

Question 1

(a) What are nucleons?

Answer: Nucleons refer to protons and neutrons. They are found in the nucleus of an atom. They are nuclear particles which are protons and neutrons.

 

(b) State Graham's law of diffusion.

Answer: Graham’s law of diffusion states that, at constant temperature and pressure, the rate of diffusion of a gas is inversely proportional to the square root of its density.

Mathematically, \( \scriptsize r \propto  \normalsize \frac{1}{\sqrt{d}} \)

 

(c) Explain briefly why aluminium does not corrode easily.

Answer: Aluminium oxide layer forms on the surface of the metal. The oxide layer forms a protective coating. This coating prevents aluminium from further attack. It is impermeable to water or air.

 

(d) State three examples of periodic properties.

Answer: 

 

(e) State two reasons why real gases deviate from ideal gas behaviour.

Answer: 

 

(f) List three uses of fractional distillation in industry.

Answer: 

 

(g) What factors determine the selective discharge of ions at the electrodes during electrolysis?

Answer: 

  1. The position of the ions in the electrochemical series
  2. Concentration of the ion in the electrolyte
  3. Nature of the electrodes used.

 

(h) State the type of reaction represented by each of the following equations:

i. C2H2  +  Br2 →  C2H5Br  +  Br

Answer: Substitution reaction

ii. C2H4   +  Br2 →  C2H4Br2

Answer: Addition reaction

 

(i) Name the products formed when butane burns in a limited supply of air.

Answer:

 

(j) List three methods of separating a solid from a liquid.

Answer:

  1. Filtraton
  2. Crystallization
  3. Evapoartion
  4. Decantation

Question 2

a) Consider the following atoms: \(\scriptsize ^R_T X\: ;\: ^S_TX\)

(i) State the phenomenon exhibited by the two atoms.

Answer: Isotopy

(ii) What is the difference between the atoms?

Answer: They have different mass numbers due to the difference in the number of neutrons

(iii) Give two examples of elements that exhibit the phenomenon stated in (ai)

Answer:

(iv) lf T is 17, write the electron configuration of the element

Answer: \( \scriptsize _{17} X = 2, \:8,\:7 \)

= 1S22S22P63S23P5

 

(b)(i) State two differences between metals and non-metals with respect to their:

I. Physical properties

Answer: 

Metals

Non – metals

Good conductor of heat and electricity

Poor conductor of heat and electricity

Malleable {can be beaten into sheets}

Non – malleable

Solid at room temperature except for mercury

Solid, liquid, or gaseous at room temperature

High meting point

Low melting point

 

II. Chemical properties.

Answer: 

Metals

Non – metals

Lose their valence electrons easily

Gain or share their valence electrons easily

Form oxides that are bases

Form oxides that are acidic neutral

Are good reducing agents

Are good oxidizing agents

Have lower electronegativity

Have higher electronegativity

Have low ionization energy

Have high ionization energy

(ii) Give one example of each for the following compounds:

I. An amphoteric oxide;

II. A hydride which evolves hydrogen when reacted with water;

Ill. A trioxocarbonate (IV) salt which is readily decomposed on heating;

IV. A chloride salt which is readily hydrolyzed in water.

Answer: 

I. Amphoteric oxides are: Al2O3; ZnO; PbO; BeO

II. Hydrides which evolve hydrogen when reacted with water are: CaCO3; MgH2; KH; LiH

III. Trioxocarbonate (iv) salts which are readily decomposed on heating are: Li2CO3; BeCO3; MgCO3; CaCO3; ZnCO3; PbCO3

IV. Carbonate salts which are readily hydrolyzed in water are: NH4Cl; AlCl3; MgCl2; SiCl4

 

(c)(i) State three characteristic properties of transition metals.

Answer:

(ii) Write the electron configuration of \(\scriptsize _{30}Zn\)

Answer: 30Zn ; 1S22S22P63S23P63d104S2

(iii.) Explain briefly why zinc is not considered as a typical transition element.

Answer: Zinc has a completely filled 3rd orbital and therefore does not have unpaired d-orbital and cannot have variable oxidation state.

 

(d) Consider the reaction represented by the following equation:-

Na2CO3(aq)  +  MgCl2(aq) → NaCl(aq)  +  MgCO3(aq)

Calculate the mass of sodium trioxocarbonate (IV) needed to produce 3.36 of magnesium trioxocarbonate (IV). [C = 12.0, O = 16.0, Na = 23.0, Mg = 24:0 ]

Solution

Na2CO3(aq)  +  MgCl2(aq) → NaCl(aq)  +  MgCO3(aq)

Na2CO3  =  (2 x 23)  +  (12)  +  (3 x 16)  = 106

MgCO3  = (24)  +  (12)  +  (16 x 3)  = 84

From the equation

84g of MgCO3 was produced from 106g NaCO3

    3.36g of MgCO3 will be produced from xg NaCO3

84g is to 106g

as 

3.36 is to xg

\( \frac{84}{106} = \frac{3.36}{x} \)

x = \( \frac{106 \: \times \: 3.36}{84} \)

= 4.24g

Question 3

(a)  (i) Define structural isomerism

Answer: Structural isomerism is the existence/occurrence of two or

(ii) State the class of alkanols to which each of the following compounds belongs:

I. CH3C(CH3)2OH

II. CH3CH(CH3)CH2OH

III. CH3CH2(CH3)OH

Answer:

 

(b) (i) Write the formulae of the products formed in the following reactions:

I. CH3CH2COOH \( \overset{K_{(s)}}{\normalsize \rightarrow}\:  \) CH3CH2COOK  +  H2

II. CH3CH2COOH \( \underset{Con.\: H_2SO_4}{\overset{C_4H_2OH,\: heat}{\normalsize \rightarrow}} \) CH3CH2COOC4H9  +  H2O

III. CH3CH2CH2CH2OH \( \underset{excess}{\overset{H^+\: KMnO_4}{\normalsize \rightarrow}} \)  CH2CH2CH2COOH  +  H2O

(ii) Name the major product(s) of each of the reactions in (b)(i).

*Potassium propanoate

*Butyl propanoate

*Butanoic acid

 

(c) A gaseous hydrocarbon R of mass 7.0g occupies a volume of 2.24dm3 at s.t.p. If the percentage composition by mass of hydrogen is 14.3, determine its

(i) empirical formula;

(ii) molecular formula.

[ H = 1.00, C = 12.0, Molar volume of gas at s.t.p, = 22.4 dm\(_2\)

Solution

Given: Gas R; mass of gass 7.0g; volume of gas = 2.24dm3 at s.t.p

Mass percentage of hydrogen = 14.3%

Find: Empirical formula, Molecular formula!

(I) Empirical formular

%  of carbon by mass = 100 - 14.3 = 85.7%

  C H
% composition 85.7 14.3
Number of atoms 12 1
Ration of atoms \( \frac{85.7}{12}\) \( \frac{14.3}{1}\)
  = 7.1415 =14.3
Divide by smaller Number \( \frac{7.1415}{7.1415}\) \( \frac{14.3}{7.1415}\)
  = 1 = 2

Empirical formular = CH2

II Molecular formular

2.24dm3 has a mass of 7.0g

22.4dm3 would have a mass of xg

x = \( \frac{22.4 \: \times \: 7}{2.24} \)

= 70g

(CH2)n  = 70

{(12) + (1 x 2)n} = 70

(12 + 2)n = 70

14n = 70

n = \( \frac{70}{14} \)

n = 5

molecular formular (CH2)n

= (CH2)5 = C5H10

 

(d) Draw the structures of the isomers of the alkene with molecular formula C4H8

Question 4

(a)(i) Name a suitable drying agent for the preparation of carbon (IV) oxide in the laboratory.

Answer:

(ii) Using one chemical test, distinguish between carbon (II) oxide and carbon (IV) oxide.

Answer: Pass/bubble each gas into lime water. If lime water turns milky, then CO2 is present. If no reaction, then CO is the gas present.

 

(b)(i) Describe briefly how oxygen and nitrogen could be obtained separately from air on an industrial scale

Answer:

(ii) State how a lighted splint can be used to distinguish between samples of oxygen and nitrogen.

Answer: 

 

(c)(i) Give one reason why bauxite is usually preferred as the ore for the extraction of aluminium.

Answer:

(ii). List two main impurities. usually present in bauxite.

Answer: 

(iii) State the function of sodium hydroxide solution in the extraction of aluminium from its ore.

Answer: To dissolve the aluminium so that the impurities can be filtered off.

(iv) Explain briefly why it is difficult to extract aluminium by chemical reduction of aluminium oxide

Answer: Aluminium is very reactive to be reduced by the commonly known reducing agents during extraction due to very strong electrovalent bonding

(v) Write an equation for the reaction of aluminium oxide with aqueous sodium hydroxide.

Answer:

Al2O3  +  2NaOH →  NaAlO2 + H2O

or

Al2O3  +  2NaOH  +  3H2O   →   2NaA(OH)4

 

(d) (i)The melting and boiling points of sodium chloride are 801C and 1413°C, respectively. Explain briefly why sodium chloride does not conduct electricity at 25°C but does so at 801°C and 1413°C.

Answer:  At 25°C, solid (state) sodium chloride ions are not free. Between 801°C and 1413°C, liquid sodium chloride ions are free.     

(ii) State the reason why sodium metal is stored under paraffin oil in the laboratory.

Answer: Sodium metal reacts quickly with moisture and carbon (iv) oxide when exposed.

 

(e)(i) State what would be observed when aqueous sodium trioxocarbonate(IV) is added to a solution containing iron (III) ions

Answer: 

(ii) Write a balanced equation for the reaction in (e)(i).

Answer: 

3Na2CO3(aq)  +  2Fe3+ → Fe2(CO3)3(g)  +  6Na+(aq) 

Question 5

(a)(i) Determine the oxidation number of sulphur in Na2S2O3

Answer: Na2S2O3 = O

2(+1)  +  2(S)  +  3(-2)  = 0

2S  = 6 – 2 = 4

S = +2

(ii) Name the allotropes of sulphur.

Answer:

(iii) State two ways in which the structure of graphite and diamond are similar.

Answer:

 

(b)(i) Name two greenhouse gases.

Answer: 

 

(ii) State one effect of an increased level of greenhouse gases on the environment.

Answer: Global warming/climate change

(iii) State one source from which nitrogen (I) oxide is released into the environment.

Answer: 

(iv) Write a chemical equation to show the effect of heat on each of the following compounds:

(I) KNO3(s)

Answer: 

KNO3(S) \(\overset{heat}{ \rightarrow} \)2KNO2(S)  +  O2(g)

(II) AgNO3(s)

Answer: 

AgNO3(S) \(\overset{heat}{ \rightarrow} \) 2Ag(s)  +  NO2(g)  + O2(g)

 

(c)(i)Describe briefly how pure crystals of calcium chloride could be obtained from a solution of calcium chloride

Answer: By heating the solution to concentrate it. Leave in a warm place. Partially evaporate solution and allow to cool. Filter crystals. Pick out crystals. Dry with filter paper.

(ii) Explain briefly each of the following observations:

I. Ammonia gas is highly soluble in water;

Answer: Ammonia readily associates with water molecules through hydrogen bonding.

II. Boiling point of chlorine is lower than that of iodine

Answer: Chlorine molecules are smaller

 

(d) Consider the reaction represented by the following equation:- 

2NaCl(s)  + H2SO4(aq) → Na2SO4(aq) + 2HCl(g)

Calculate the volume of HCl gas that can be obtained at s.t.p. from 5.85 g of sodium. chloride.

[Na = 23.0; Cl = 35.5; molar volume of gas at s.t.p. = 22.4dm3]

Solution:

Given: mass of NaCl = 5.85g, s.t.p,

NaCl = 23.0 + 35.5 = 58.5g

HCl = 1 + 35.5 = 36.5

According to the equation

2NaCl = 2 x 58.5g of NaCl equivalent 2 x 36.5g of HCl

5.85g of NaCl equivalent x g of HCl

x = \( \frac{2 \: \times \: 36.5 \: \times \: 5.85 }{2 \: \times \: 58.5} \)

x = 3.65g

∴ Volume at s.t.p = \( \frac{3.65 }{36.5} \scriptsize \: \times \: 22.4 \)

= 2.24dm3