WAEC 2021 Chemistry | Essay

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Question 1 View Details
Question Parts
(a)
Distinguish between molecular formula and structural formula.
(b)
List three factors that determine the ionization energy of an atom.
(c)
State the two conditions necessary for the establishment of a chemical equilibrium.
(d)
Consider the following table.
(e)
State Graham's law of diffusion.
(f)
Consider the following salts: \( \mathrm{Mg}\left(\mathrm{NO}_{3}\right)_{2}, \mathrm{CaCO}_{3}, \mathrm{Na}_{2} \mathrm{SO}_{4} \). State which of the salts is/are:
(g)
Classify each of the following products as addition polymer or condensation polymer:
(h)
Define atomic radius.
(i)
Explain briefly why ethanol has a higher boiling point than propane even though they both have comparable molar masses.
(j)
State three significance of the \( p H \) value in everyday life.
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Question 2 View Details
Question Parts
(a)
(i) State two characteristics of a homologous series.
(a)
(ii) Explain briefly why there are differences in the reaction of ethane and ethene.
(b)
(i) When crystals of sodium chloride were warmed with concentrated tetraoxosulphate (VI) acid, a gas was evolved. Name the gas.
(b)
(ii) State two physical properties of the gas.
(b)
(iii) Write a balanced chemical equation for the reaction.
(c)
(i) What are hydrocarbons?
(c)
(ii) State two natural sources of hydrocarbons.
(c)
(iii) A hydrocarbon contains \( 83 \% \) of carbon by mass. Calculate its empirical formula. \( [H=1.0, C=12.0] \)
(d)
Draw and label a diagram of a set-up that could be used to electroplate a copper ornament with silver.
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Question 3 View Details
Question Parts
(a)
(i) In an experiment, \( 25.0 c m^{3} \) of \( \mathrm{H}_{2} \mathrm{SO}_{4} \) completely neutralized \( 24.0 c m^{3} \) of a 0.150 mol dm \( { }^{-3} \) aqueous KOH using a suitable indicator. Write a balanced chemical equation for the reaction.
(a)
(ii) Calculate the concentration of the acid solution.
(b)
(i) A burning magnesium ribbon was placed in a gas jar containing carbon (IV) oxide. Write an equation for the reaction.
(b)
(ii) Explain briefly why the magnesium ribbon burns in carbon (IV) oxide although the gas does not support combustion.
(b)
(ii) Calculate the percentage by mass of nitrogen in magnesium trioxonitrate (V). \( [N=14.0, O=16.0, M g=24.0] \)
(c)
(i) Consider the following organic compound: \( \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}=\mathrm{CHCOOH} \). State two chemical reactions which could be used to identify the compound.
(c)
(ii) What would be observed in each of the reactions stated in 3(c)(i)?
(d)
Describe briefly how soap is manufactured using pellets of sodium hydroxide and vegetable oil.
(e)
Define the term electronegativity.
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Question 4 View Details
Question Parts
(a)
(i) What is the structure of (I) graphite (II) diamond?
(a)
(ii) Explain briefly why diamond is hard and a non-conductor of electricity while graphite is soft and an electrical conductor.
(b)
(i) State what is achieved at each of the following stages in the purification of town water supply: (I) aeration; (II) screening; (III) sedimentation.
(b)
(ii) Name two substances responsible for hardness in water.
(b)
(iii) State two methods for the removal of hardness in water.
(b)
(iv) Give one disadvantage of hard water.
(c)
(i) Describe briefly the extraction of tin from its ore.
(c)
(ii) Write a balanced chemical equation for the reaction.
(c)
(iii) Write an equation for the reaction of tin with: (I) oxygen, (II) chlorine.
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Question 5 View Details
Question Parts
(a)
(i) With the aid of an equation, explain briefly why aluminium metal is not affected by air.
(a)
(ii) In the extraction of aluminium from bauxite, state the: (I) substance used for purifying the ore; (II) composition of the mixture electrolysed.
(b)
ZnO is an amphoteric oxide. Write equations to illustrate this statement.
(b)
(i) List three uses of sodium trioxocarbonate (IV).
(b)
(ii) Explain briefly why a solution of trioxonitrate (V) acid turns yellowish on storage for some time.
(b)
(iii) Describe briefly how trioxonitrate (V) ions could be tested for in the laboratory.
(c)
(i) Write balanced chemical equations for the preparation of hydrogen chloride: (I) using concentrated \( \mathrm{H}_{2} \mathrm{SO}_{4} \) (II) by direct combination of its constituent elements.
(c)
(ii) State one use of hydrogen chloride.
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