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

The percentage yield is calculated using the formula:

$\text{Percentage Yield} = \left( \frac{\text{actual yield}}{\text{theoretical yield}} \right) \times 100$

1. Actual yield of CaO is given as: 5.450 g.
2. Theoretical yield of CaO: 5.600 g.

Now, substituting the values in:

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

Thus, the percentage yield of calcium oxide is 97.3%.

The data shows a decreasing trend in the mass of solid remaining as time progresses. This indicates that calcium carbonate is decomposing into calcium oxide and carbon dioxide as heat is applied. The rapid decrease in mass during the initial minutes reflects the release of carbon dioxide gas, with the rate of mass loss slowing down over time as the reaction approaches completion.

It is impossible to be sure the reaction is complete because the data only shows decreasing mass without reaching a stable endpoint. The solid remaining may still contain unreacted calcium carbonate, and the mass may continue to decrease if further carbon dioxide is released.

To find the relative formula mass of calcium carbonate, we sum the relative atomic masses:

1. Carbon (C) = 12
2. Oxygen (O) = 16 x 3 = 48 (since there are 3 oxygen atoms)
3. Calcium (Ca) = 40

Total = 12 + 48 + 40 = 100

Thus, the relative formula mass of calcium carbonate, CaCO₃, is 100.

Atom economy measures the efficiency of a reaction in terms of the amount of desired product formed. It is calculated as:

$\text{Atom Economy} = \left( \frac{\text{mass of desired product}}{\text{total mass of reactants}} \right) \times 100$

1. Desired product (CaO) mass = 56 g.
2. Total mass of reactants (CaCO₃) mass = 100 g.

Now substituting the values in:

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

Thus, the atom economy for the formation of calcium oxide is 56%.