WAEC 2023 Chemistry | Essay

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Question 1 View Details
What is transition element?
Question Parts
(a)
Consider the electron configuration of the following elements: \[ \begin{array}{l} A=2: 8: 6 ; B=2: 8: 2 ; C=2: 8: 1 ; \\ D=2: 8: 8 \end{array} \] State the element which forms a: (i) double charged cation;
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Question 2 View Details
In an experiment, 20.0 cm³ of a solution containing 4 g dm⁻³ of sodium hydroxide was neutralized by 8.0 cm³ of dilute tetraoxosulphate (VI) acid:
Question Parts
(a)
(i) write a balanced equation for the reaction; (ii) calculate the concentration of the acid in mol dm⁻³.
(b)
(i) State two postulates of the Kinetic theory of gases which real gases do not obey. (ii) Explain briefly why gases do not obey the postulates stated in 2b(i)
(c)
(i) name the compound; (ii) name the two structural isomers of the compound; (iii) state the chemical process involved in the preparation of the compound from starch; (iv) write the chemical equation for the steps involved in the process in 2(c)(iii); (v) name two enzymes involved in the process in 2(c)(iii).
(d)
Explain briefly the term structural isomerism.
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Question 3 View Details
A compound contains 52.2% C, 13.1% H and Oxygen only. The vapour density of the compound is 23.
Question Parts
(a)
(i) Determine its empirical formula; (ii) Determine its molecular formula; (iii) The compound reacts with sodium metal to produce hydrogen gas and when warmed with acidified KMnO₄ gives a solution which turns from purple to colourless. It also forms a sweet smelling liquid when heated with ethanoic acid in the presence of concentrated H₂SO₄. I. name the functional group present in the compound; II. draw the structural formula of the compound. [H=1.0, C=12.0, O=16.0]
(b)
Outline the chemical equations for the production of ethanol from cooked cassava.
(c)
(i) Explain briefly why a piece of aluminium does not react with water. (ii) How can a pure sample of aluminium chloride crystals be prepared from aluminium.
(d)
Describe how water can be separated from aqueous CuSO₄.
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Question 4 View Details
Starting with calcium chloride, describe briefly how a solid sample of calcium trioxocarbonate (IV) can be prepared in the laboratory.
Question Parts
(a)
(b) With relevant equations outline the procedure for the purification of impure copper.
(c)
(i) Copper reacts with concentrated trioxonitrate (V) acid: write a balanced chemical equation for the reaction; (ii) state what would be observed in the reaction; (iii) state why the copper is oxidized; (iv) an excess of copper is added to 25.0 cm³ of 16.0 mol dm⁻³ NHO₃. Calculate the volume of the gas formed at s.t.p. [H=1.0, N=14.0, O=16.0, Cu=63.0; Molar volume of gas at s.t.p. =22.4 cm³]
(d)
(i) Pure HNO₃ is a colourless liquid but when exposed to air, it turns yellow-ish-brown in colour. Explain briefly this observation. (ii) Write a balanced equation for the laboratory preparation of hydrogen trioxonitrate (V) acid.
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Question 5 View Details
Describe how iron and aluminium reacts with each of the following substances:
Question Parts
(a)
(i) dilute H₂SO₄; (ii) dilute HNO₃.
(b)
(i) Write an equation for the burning of sulphur in air. (ii) Name the catalyst used in the contact process. (iii) In the contact process, why is an excess of air used? (iv) Why is it necessary to cool the catalyst used in 5b(ii) (v) Give a reason why the air used in the contact process needs to be as clean as possible. (vi) State two reasons why SO₂ should not be discharged into the atmosphere.
(c)
(i) State the reagent and condition used in the laboratory preparation of chlorine. (ii) State two uses of chlorine.
(d)
(i) Name the drying agents for each of the following gases: I. hydrogen; II. sulphur (IV) oxide; III. ammonia. (ii) State the components of the following alloys: I. Bronze; II. Brass.
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