WAEC Chemistry 2025 Objective — Question 29
Question 29 of 50 from the West African Examinations Council (WAEC) Chemistry 2025 Objective paper, with the correct answer and a full explanation.
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The percentage by mass of water in Na2CO3.10H2O is [Na2CO3 = 106, H2O = 18]
- A. 68.4%
- B. 62.9%Correct
- C. 9.7%
- D. 6.3%
Explanation
Molar mass of Na2CO3.10H2O = 286 g/mol (given). Mass of water = 10 x 18 = 180 g. Percentage of water = (180g/286g) x 100% = 62.93%.
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