WAEC Chemistry 2019 Objective — Question 20
Question 20 of 50 from the West African Examinations Council (WAEC) Chemistry 2019 Objective paper, with the correct answer and a full explanation.
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A sample of air was bubbled into water. The pH of the water slowly changed from 7 to 6. Which of the following gases in the sample caused the change?
- A. Carbon(IV) oxideCorrect
- B. Carbon(II) oxide
- C. Nitrogen
- D. Oxygen
Explanation
A drop in pH (7→6) indicates the gas is acidic in water. Carbon(IV) oxide (CO2) forms a weakly acidic solution (carbonic acid); CO, N2 and O2 are neutral in water.
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