Waec Chemistry 2020 Past Questions and Answers

Question 51:

• WAEC 2020

(a)(i) State Faraday's first law of electrolysis. (ii) Distinguish between a strong electrolyte and a weak electrolyte
(b) State one chemical property of ethyne.
(c)( i) What is meant by the tern unsaturated hydrocarbon? (ii) Complete the following reaction equation: CH\(_3\) + CH\(_3\)OH-> (iii) Name the major product formed in the cation stated in 1(c)(ii).
(d) State one way by which the rate of esterification could be increased.
(e) Consider the reaction represented by the following equation: Zn + H\(_2\)SO4 → ZnOS\(_4\) + H\(_2\) . If 3.75g of Zn dust was added to excess H\(_2\)SO\(_4\). Calculate the number of molecules of hydrogen gas produced. [ Zn = 65.0, Na = 6.02 X10\(^23\) ].
(f) State one effect of global warming.
(g) Consider the following reaction equation:
A. Pb(NO\(_3\)) +H\(_2\)S --> PbS + 2HNO\(_3\);
B. H\(_2\) + C\(_2\)H\(_4\) → C\(_2\)H\(_6\).
C. Zn(OH)\(_2\) + 2OH → [ Zn(OH)\(_4\) ]\(^2\).
(i) Which of the equations represent(s) redox process? (ii) State the change in Oxidation number of the species that are oxidized or reduced. (h)(i) State two of the main concepts of Bohr's model of the atom. (ii) State the limitations of Bohr's model. (i) List three factors that could influence the equilibrium position of a reversible reaction. (j) Calcium trioxocarbonate(iv) powder is added to separate equimolar solutions of hydrochloric acid and ethanoic acid. State one: (i) similarity in the observation in both reactions: (ii) difference in the observation in both reactions.

Question 52:

• WAEC 2020

WAEC 2020



(a) Consider the following compounds: (i) What is the relationship between the compounds labeled A and B? (ii) Name each of compounds A and B. (iii) Will the chemical properties of compounds A and B be the same? (iv) Give the reason for the answer stated in 2(a)(ii).
(b)(i) Give two characteristic features of boiling, (ii) What would be the effect of each of the following conditions on the boiling point of water? I. Addition of crystals of sodium chloride. II. Reduction of the atmospheric pressure. (iii) State one way in which boiling differs from evaporation.
(c)(i) Differentiate between an unsaturated solution and a saturated Solution. (ii) State two ways by which a saturated solution could be made to dissolve more solute. (iii) State one factor that could affect the solubility of a solid in a liquid. (d)(i) Define the term mole .
(ii) Consider the following reaction equation: MgO + 2HCI → MgCl\(_2\) + H\(_2\). What mass of magnesium Oxide is needed to neutralize 25.0 cm3 of 0.1 mol dm-3 hydrochloric acid? [O= 16.0; Mg = 24.0]. (e) State three physical properties of metals.

Question 53:

• WAEC 2020

WAEC 2020

(a) In the laboratory preparation of dry chlorine gas, state the: I. reagents used; II. drying agent III. the mode of collection.
(i) Write the equation for the preparation of chlorine gas. (iii) Write an equation to show how chlorine reacts with hot concentrated NaOH.
(b)i). Name the main raw materials used for the extraction of iron in the blast furnace. (ii) Write the equations of the reactions taking place in the blast furnace.
(iii) What is the name given to the iron obtained directly from the blast furnace? (iv) State why the iron named in 4(b)(iii) have a relatively low melting point?
(c) The following equation represents one of the reaction steps involved in the contact process: 2SO\(_2\) + O\(_2\) ⇌ 2SO\(_3\) ΔH = -395.7 kJ mo-l
(i) Why is the SO\(_3\) produced during the reaction not dissolved directly in water to form H\(_2\)SO\(_4\)? (ii) Why is the H\(_2\)SO\(_4\) regarded as a heavy chemical? (iii) State the property exhibited by tetraoxosulphate (VI) acid in each of the following reaction equations.
I. Pb(NO\(_3\))\(_2\) + H\(_2\)SO\(_4\)→ PbSO\(_4\) + 2HNO\(_3\) (d) Write a balanced chemical equation for the reaction between propanol and sodium

Question 54:

• WAEC 2020

WAEC 2020

(a) In an equilibrium reaction between gases Q and R, to form QR, the energy content of the reactants is 100 KJ and that of the product is 54 kJ. 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 il. enthalpy change ΔH of the reaction. (iii) Write a balanced equation for the reaction. (iv) Give a reason for the answer given in 3(C)(iv). (iv) State whether the reaction is exothermic or endothermic.
(b) Consider the following table:

Element	E	F	G	H
Atomic number	7	9	12	13

(i) Write the electron configuration for each of the elements. Element E, F, G, H 12 13 (ii) State: I. two elements that are metals; II. the elements(s) most likely to form an ion with a charge of +3; III. the element(s) which belong(s) to group VII. on the periodic table; IV. the formula of the compound formed between F and G. Atomic
(c) Define the term isotopy (d) Name the three building blocks of matter.

Question 55:

• WAEC 2020

.(a)(i) Name two gases that can be used to perform the fountain experiment. (ii) What is the aim of he fountain experiment? (iii) Describe briefly the fountain experiment.
(b)(i) Name two chemical industries. (ii) State three effects of a chemical industry on the community in which it is sited.
(c)(i) Name three products of the destructive distillation of coal. (ii) Give one use each of any two of the products named in 5(c)(1).
(d)(i) Name two substances responsible for hardness in water. (ii) State two methods for the removal of hardness in water. (iii) State two advantages of hard water.