Copper forms two oxides, Cu2O and CuO - AQA - GCSE Chemistry - Question 8 - 2019 - Paper 1

The excess hydrogen must be burnt off to prevent any unreacted hydrogen from escaping into the environment, as hydrogen is highly flammable and poses a risk of explosion.

To find the mass of copper and water produced, we can refer to Table 5:

• Mass of copper: The mass of the oxide of copper before heating is 115.47 g. After heating for 2 minutes, the mass is 114.62 g. Thus, the mass of copper produced can be calculated as follows:

$\text{Mass of copper} = 115.47\,g - 114.38\,g = 1.09\,g$

• Mass of water: The total mass of tube B and contents at start was 120.93 g, and after the reaction, it is 123.38 g. Therefore, the mass of water produced is:

$\text{Mass of water} = 123.38\,g - 120.93\,g = 2.45\,g$

To determine which equation is correct for the formation of 2.54 g of copper and 0.72 g of water, we shall analyze the mole ratio and compatibility:

• In Equation 1 (Cu2O), 1 mole of Cu2O produces 2 moles of Cu and 1 mole of H2O.
• In Equation 2 (CuO), 1 mole of CuO produces 1 mole of Cu and 1 mole of H2O.

Using relative atomic masses, we can see which ratio fits:

• For Equation 1, with 0.04 moles of Cu2O:

$0.04 \text{ moles Cu} = 0.08 \text{ g} \quad (2\,Cu)$

• For Equation 2, with 0.04 moles of CuO:

$0.04 \text{ moles Cu} = 0.04 \text{ g} \quad (1\,Cu)$

Thus, the data aligns more closely with Equation 1 for this experiment as it accounts for both copper and water produced.