Neco Model Questions Vol1 2021 Chemistry Question 4

A gravimetric analysis was carried out to determine the amount of calcium in a sample of unknown composition. The procedure was as follows: 1. A 0.500 g sample of the unknown solid was accurately weighed and transferred to a 250 mL beaker. 2. To the beaker, 100 mL of 0.200 M sodium carbonate solution was added and the mixture was gently heated until a white precipitate of calcium carbonate formed and the solution became clear. 3. The precipitate was filtered, washed with de‑ionised water and dried to constant mass. The mass of the dried CaCO₃ precipitate was recorded as 0.312 g. 4. The dried precipitate was then placed in a crucible and heated strongly in a muffle furnace at 900 °C for 30 min to convert it to calcium oxide (CaO). After cooling in a desiccator, the mass of the CaO obtained was 0.176 g. Using the data above, answer the following questions: