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Chemistry Past Questions and Answers

Waec Chemistry Questions

Question 71:

Locally produced soap in which wood ash is used as the base is usually soft because the wood ash contains a lot of

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A Sodium ions
B Potassium ions
C Lithium ions
D Calcium ions
E Magnesium ions

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Question 72:

Why is potassium fluoride added to the electrolyte in the extraction of sodium from fused sodium chloride?

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A Pure sodium chloride does not conduct electricity
B Potassium fluoride prevents the sodium produced from attacking the electrodes
C Potassium fluride increases conductivity
D Potassium fluride reduces the temperature at which sodium chloride fuses
E The potassium fluride acts as a catalyst

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Question 73:

The rate of the hydrogen in the reaction Zn_(s) + 2HCI _(aq) â†’ ZnCI _2(g) + H _2(aq) + H _2(g) can be increased by

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A Using Zinc powder instead of Zinc granules
B Using dilute instead of concentrated hydrochloric acid
C Cooling the container in which the mixture is placed
D Using an alloy of zinc instead of pure zinc
E Using hydrogen chloride gas instead of hydrochloric acid solution

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Question 74:

Octane number is highest in petrol containing a high proportion of

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A Heptane
B Octane
C 2-methylpentane
D 2, 4-dimethylpentane
E 2,2,4-trimethylpentane

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Question 75:

Given the following half-cell reaction; 2Cl_(aq) â†’ CI_2(g) + 2e, how many mole of electrons will be required to produce 1.12dm³ of chlorine gas at s.t.p? (Molar volume of a gas at s.t.p. = 22.4dm ³)

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A 1.00
B 0.40
C 0.20
D 0.10
E 0.01

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