This question is about gases - Edexcel - GCSE Chemistry Combined Science - Question 2 - 2022 - Paper 1

The gas that bleaches damp litmus paper is B. chlorine. Chlorine is known for its bleaching properties as it reacts with the dye in the litmus paper.

To find the mass of solid remaining, we first need the molar mass of calcium carbonate (CaCO₃) which is approximately 100 g/mol. The reaction produces calcium oxide (CaO) and carbon dioxide (CO₂).

Given:

• Mass of CaCO₃ = 5.000 g
• Molar mass of CaO = 56 g/mol
• Molar mass of CO₂ = 44 g/mol

Using stoichiometry, we can calculate the mass of CO₂ produced:

1. Calculate moles of CaCO₃:

   $n = \frac{mass}{molar mass} = \frac{5.000 ext{ g}}{100 ext{ g/mol}} = 0.0500 ext{ mol}$

2. In the decomposition reaction:

   • 1 mol CaCO₃ produces 1 mol CaO and 1 mol CO₂.

Thus, 0.0500 mol of CaCO₃ will produce:

• 0.0500 mol of CaO
• 0.0500 mol of CO₂

3. Calculate the mass of CO₂:

   $mass_{CO₂} = 0.0500 ext{ mol} \times 44 ext{ g/mol} = 2.20 ext{ g}$

4. Finally, subtract the mass of CO₂ from the initial mass:

   $mass_{remaining} = 5.000 ext{ g} - 2.20 ext{ g} = 2.80 ext{ g}$

Thus, the mass of solid remaining is 2.80 g.