WAEC Past Questions and Answers

8,256.

If the solubility of KHCO₃ is 0.40 mole dm^{-3 at room temperature , calculate the mass of KHCO₃ in 100dm³ of the solution at this temperature. [KHCO₃ = 100hmol]}

4.0g

10.0g

40.0g

100.0g

View answer & explanation

Correct answer is A

No explanation has been provided for this answer.

8,257.

Which of the following compounds dissolves in water to form a solution with pH below 7?

Sodium tetraoxosulphate (VI)

Potassium hydroxide

Ammonium chloride

Sodium trioxocarbonate (IV)

View answer & explanation

Correct answer is C

No explanation has been provided for this answer.

8,258.

Which of the following is an acid salt?

NH₄CI

MgSO₄ 7H₂O

CH₃COONa

NaHCO₃

View answer & explanation

Correct answer is D

No explanation has been provided for this answer.

8,259.

An exothermic reaction is one which involves

attainment of dynamic equilibrium

loss of heat to the surrounding

evolution of gas as it proceeds

positive change in value of enthalpy

View answer & explanation

Correct answer is B

No explanation has been provided for this answer.

8,260.

30cm3 pf hydrogen at s.t.p combine with 20cm3 of oxygen to form steam according to the following equation 2H2(g) + O2(g) → 2H2O(g).

Calculate the total volume of the gaseous mixture at the end of the reaction

50cm³

35cm³

30cm³

25cm³

View answer & explanation

Correct answer is B

2H\(_2\)(g) + O\(_2\)(g) → 2H\(_2\)O(g).

2 volumes of H\(_2\)(g) and 1 volume of O\(_2\)(g) produced 2 volumes of H\(_2\)O\(_2\)

ratio of reacting volumes

30cm\(^3\) + 15cm\(^3\) → 30cm\(^3\)

30cm\(^3\) of Hydrogen requires 15cm\(^3\) of oxygen to produce 30cm\(^3\) of water.

Excess oxygen: 20cm\(^3\) – 15cm\(^3\) = 5cm\(^3\)

Total volume of gaseous mixture: 5cm\(^3\) of Oxygen + 30cm\(^3\) of Water = 35cm\(^3\)