Chemistry 2020 Past Questions | WAEC

Study the following Chemistry past questions and answers for JAMBWAEC  NECO and Post-JAMB. Get prepared with official past questions and answers for upcoming examinations.

46. which of the following quantities is a molar quantity?

  • A. Molarity
  • B. Molar mass
  • C. Mass concentration
  • D. Molality

47. Dilution factor is the?

  • A. amount of distilled water that is added to the concentrated solution to dilute it
  • B. Quantity of distilled water added to l dm33 of the concentrated solution to give the dilute solution
  • C. number of times the volume of the concentrated solution is diluted to give the dilute solution
  • D. act of diluting the concentrated solution to obtain the dilute solution

48.  Calcium chloride is an ionic compound. Which of the following statements account for its ionic character?

  1. Calcium has high ionization energy.  II. Calcium has low ionization energy. III. Chlorine has high electron afinity. IV. Chlorine has high 1onization energy.
  • A. I and Il only
  • B. 1, II and IV only
  • C. II, IIl and IV only
  • D. I, II, III and IV

49. An example of a biodegradable pollutant is?

  • A. plastic
  • B. sewage
  • C. carbon (II) oxide
  • D. hydrogen sulphide

CHEMISTRY 2020 WAEC QUESTIONS THEORY WITH SOLUTIONS

  1. (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: CH3 + CH3OH-> (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 + H2SO4 → ZnOS4 + H2 . If 3.75g of Zn dust was added to excess H2SO4. Calculate the number of molecules of hydrogen gas produced. [ Zn = 65.0, Na = 6.02 X1023 ].

 (f) State one effect of global warming.

(g) Consider the following reaction equation:

  1. Pb(NO3) +H2S –> PbS + 2HNO3;
  2. H2+ C2H4→ C2H6.
  3. 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.

(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 → MgCl2 + H2. 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.

  1. (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: 2SO2 + O2   2SO3 ΔH = -395.7 kJ mo-l

(i) Why is the SO3 produced during the reaction not dissolved directly in water to form H2SO4? (ii) Why is the H2SO4 regarded as a heavy chemical? (iii) State the property exhibited by tetraoxosulphate (VI) acid in each of the following reaction equations.

  1. Pb(NO3)2+ H2SO4→ PbSO4+ 2HNO3 (d) Write a balanced chemical equation for the reaction between propanol and sodium
  1. (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.

4.(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

  1. All your burette readings (initial and final), as well as the size of your pipette, must be recorded but no account of the experimental procedure is required. All calculations must be done in your answer booklet.

A is a solution containing 5.00 g of HNO33 in 500 cm\(^3) of solution. B is a solution of NaOH of unknown concentration.

(a) Put A into the burette and titrate it with 20.0 cm33 or 25.0 cm33 portions of B using methyl orange as an indicator. Repeat the titration to obtain concordant titre values. Tabulate your results and calculate the average volume of acid used. Equation of the reaction is HNO3(aq)3 + NaOH(aq) → NaNO3(aq)3 + H2O(l)

(b) From your results and the information provided. calculate the: (i) concentration ot A In mol dm-3

(ii) concentration of B in mol dm-3

(iii) concentration of B in gdm-3

 (iv) mass of NaNO33 formed. If 250 cm3 of NaOH were neutralised. [Molar mass of NaOH = 40g mol−1, NaNO3 = 85 gmol−1. Credit will be given for strict adherence to the instructions. for observations precisely recorded and for accurate inferences. All tests, observations and inferences must be clearly entered in this booklet, in ink, at the time they are made.

  1. C is an organic compound. Carry out the following exercises on C. Record your observations and identity any gas(es) evolved. State the conclusions you draw from the results of each test.

(a) Put about 10 drops of C on a watch glass and ignite it using a burning splint.

(b)(i) Put about 1 cm33 of C in a test tube and add about 1 cm33 of distilled water. Shake the test tube.

(ii) Put about 1 cm3 of C in a test tube and add about 2 cm3 of acidified K2Cr2O7 solution. Warm the mixture gently and leave to stand for 5 minutes.

(c) Put few crystals of specimen D in a test tube and add about 2cm3 of C followed by about 2 cm3 of 10 % NaOH(aq) Shake the test tube vigorously.

(d) State the class of compounds to which C belongs.
 

  1. (a) A zinc salt, E when heated strongly, produced a brown gas with pungent smell, a colourless gas that rekindled a glowing splint, and a residue that was allowed to cool.

(i) identify the salt E.

(ii) Write an equation for the decomposition of E.

(iii) State what would be observed when the residue was allowed to cool.

(b) Describe how 250cm3 of 0.2 mol dm33 H2SO4 could be prepared from 150 cm3 of a 1.0 mol dm33 stock solution of the acid.

(c) State the effect of aqueous solution of Al2(SO4)3 on litmus paper

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