To analyze the situation:
The balanced chemical equation for the decomposition of water is:
\[ 2H_2O \rightarrow 2H_2 + O_2 \]
From the equation, we can see the mole ratio:
- 2 moles of water produce 2 moles of hydrogen and 1 mole of oxygen.
Next, we can calculate the mass of water based on the collected gases:
- The molar mass of hydrogen (H₂) is approximately 2 g/mol.
- The molar mass of oxygen (O₂) is approximately 32 g/mol.
From the problem:
- 112 g of hydrogen gas:
\[ \text{Moles of } H_2 = \frac{112 \text{ g}}{2 \text{ g/mol}} = 56 \text{ moles of } H_2 \]
Since 2 moles of H₂ come from 2 moles of H2O, this corresponds to: \[ \text{Moles of } H_2O = 56 \text{ moles of } H_2 \Rightarrow 56 \text{ moles of } H_2O \]
- 888 g of oxygen gas:
\[ \text{Moles of } O_2 = \frac{888 \text{ g}}{32 \text{ g/mol}} = 27.75 \text{ moles of } O_2 \]
Since 1 mole of O₂ comes from 2 moles of H₂O, this corresponds to: \[ \text{Moles of } H_2O = 27.75 \text{ moles of } O_2 \times 2 = 55.5 \text{ moles of } H_2O \]
To determine the mass of water used, we can use the average of the moles calculated:
-
Using the moles from hydrogen: \[ \text{Mass of } H_2O = 56 \text{ moles} \times 18 \text{ g/mol} = 1008 \text{ g} \]
-
Using the moles from oxygen: \[ \text{Mass of } H_2O = 55.5 \text{ moles} \times 18 \text{ g/mol} = 999 \text{ g} \]
Hence, averaging these values, we can conclude that approximately 1000 g of water were used.
Therefore, based on the law of conservation of mass, the correct response is:
Student B, because of the law of conservation of matter.