WAEC Chemistry 2022 Objective — Question 15

Question 15 of 50 from the West African Examinations Council (WAEC) Chemistry 2022 Objective paper, with the correct answer and a full explanation.

If 5.0g of marble reacts with 25.0 cm³ hydrochloric acid, which of the following combinations has the fastest reaction rate?

A. Marble chips and 2.0 mol dm⁻³ HCl(aq)
B. Marble chips and 2.5 mol dm⁻³ HCl(aq), powdered marble and 2.5 mol dm⁻³ HCl(aq)
C. Powdered marble and 2.5 mol dm⁻³ HCl(aq)Correct
D. Powdered marble and 2.0 mol dm⁻³ HCl(aq)

Explanation

Powdered marble reacts faster than marble chips because the powder provides a larger surface area of contact with the acid, and using the higher acid concentration (2.5 mol dm⁻³) further increases the rate.

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