### Chemistry Past Questions

4111

Which of the following scientists discovered the electrons?

• A. Joseph J. Thompson
• D. Ernest Rutherford
WAEC 2021
4112

(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

 Element A B C Ionization energy KJ mol$$^{-1}$$ 619 518 594

(d)(i) State which of the elements is the strongest reducing agent.

(ii) Give a reason for the answer stated in (d)(i)

(e) State Graham's law of diffusion

(f) Consider the following salts: Mg(NO$$_{3}$$)$$_{2}$$, CaCO$$_{3}$$, Na$$_{2}$$SO$$_{4}$$. State which of the salts is/are:
(ii) insoluble in water.

(g) Classily each of the following products as addition polymer or condensation polymer:
(i) protein:
(ii) perspex:
(iii) nylon.

(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 pH value in everyday life.

WAEC 2021
4113

(a)i. State two characteristics of a homologous series.

(ii) Explain briefly why there are differences in the reaction of ethane and ethene.

(b) When crystals of sodium chloride were warmed with concentrated tetraoxosulphate( VI) acid, a gas was evolved.
(i) Name the gas.
(ii) State two physical properties of the gas.
(iii) Write a balanced chemical equation for the reaction.

(c)i. What are hydrocarbons?
(ii) State two natural sources of hydrocarbons.
(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

WAEC 2021
4114

(a) In an experiment, 25.0 cm$$^{3}$$ of H$$_{2}$$SO$$_{4}$$ completely neutralized 24.0 cm$$^{3}$$ of a 0.1 50 mol dm$$^{-3}$$ aqueous KOH using a suitable indicator.

(i) Write a balanced chemical equation for the reaction.

(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.
- Explain briefly why the magnesium ribbon burns in carbon(lV) oxide although the gas does not support combustion.
- Calculate the percentage mass of nitrogen in magnesium trioxonitrate (V). |N = 140. O = 16.0. Mg = 24.01]

(c) Consider the following organic compound: CH$$_{3}$$CH$$_{2}$$CH = CHCOOH.

(i) State two chemical reactions which could he sed te identify the compound.

(ii) What would be observed in each of the reactions stated in c(i)

(d) Describe briefly how soap is manufactured using pellets of sodium hydroxide and vegetable oil

(e) Define the term electronegativity

WAEC 2021
4115

(a) What is the structure of:

(i) graphite:
(ii) diamond
(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:

- aeration;
- screening
- sedimentation.

(ii) Name two substances responsible for hardness in water.

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

(iv) Give one disadvantage of hard water

(c)i). Describe briefly the extraction of tin from its ore.

(ii) Write a balanced chemical equation for the reaction.

(iii) Write an equation for the reaction of tin with:
- oxygen;
- chlorine.

WAEC 2021