Calcium carbonate decomposes on heating to form calcium oxide and carbon dioxide - Edexcel - GCSE Chemistry - Question 10 - 2019 - Paper 1

Percentage yield can be calculated using the formula:

$ext{Percentage Yield} = \left( \frac{\text{Actual Yield}}{\text{Theoretical Yield}} \right) \times 100$

Actual yield of CaO = 5.450 g

Theoretical yield of CaO = 5.600 g

Plugging in the values:

$\text{Percentage Yield} = \left( \frac{5.450}{5.600} \right) \times 100 = 97.3\%$

The possible reason for the mass of solid left being less than expected is:

A some solid was lost from the crucible.

The data in Figure 11 indicates a decreasing trend in the mass of solid remaining as time progresses. This is expected as the heating process causes the calcium carbonate to decompose, which results in a gradual loss of mass due to the release of carbon dioxide gas (CO₂). Initially, there is a greater mass loss, which slows down as the reaction approaches completion.

It is impossible to be sure the reaction is complete because the remaining mass of solid may still contain unreacted calcium carbonate or other substances. Without further experimental data, one cannot confirm that all reactants have been fully converted to products.

To calculate the relative formula mass of calcium carbonate (CaCO₃), we add the atomic masses of its constituent elements:

• C: 12 g/mol
• O: 16 g/mol (there are 3 O atoms)
• Ca: 40 g/mol

Therefore,

$\text{Relative Formula Mass of CaCO₃} = 12 + (3 \times 16) + 40 = 100 ext{ g/mol}$

Atom economy is calculated using the formula:

$\text{Atom Economy} = \left( \frac{\text{Mass of Desired Product}}{\text{Total Mass of Reactants}} \right) \times 100$

Mass of desired product (CaO) = 56 g/mol

Total mass of reactants (CaCO₃) = 100 g/mol

Thus,

$\text{Atom Economy} = \left( \frac{56}{100} \right) \times 100 = 56\%$