Answer:
(b) (i) To determine the percentage by mass of potassium in K₂CO3, we can use the molar masses of the individual elements in the compound. The molar mass of K₂CO₃ is 138.21 g/mol. The molar mass of potassium is 39.098 g/mol and the molar mass of carbon and oxygen is 12.01 and 16.00 respectively.
The mass of potassium in K₂CO₃ is 2*39.098 = 78.196 g
The mass of K₂CO₃ is 138.21 g
percentage of potassium in K₂CO₃ = (mass of potassium / mass of K₂CO₃) * 100 = (78.196 / 138.21) * 100 = 56.6%
(b) (ii) If the crystals of potassium carbonate are a hydrate, K₂CO₃.2H₂O, it means that there is water molecules present in the crystal structure. The mass of water in the hydrate will not contribute to the percentage of potassium in the hydrate. Therefore, the percentage of potassium in the hydrate will be lower than the value stated in (1)