Question

Passing an electric current through a sample of water (H2O) can cause the water to decompose into hydrogen gas (H2) and oxygen gas (O2) according to the following equation. 2H2O 2H2 + O2 The molar mass of H2O is 18.01 g/mol. The molar mass of O2 is 32.00 g/mol. What mass of H2O, in grams, must react to produce 50.00 g of O2?

Answer 1

Answer: The mass of water that must be reacted is 56.28 grams.

Explanation:

To calculate the number of moles, we use the equation:

$\text{Number of moles}=\frac{\text{Given mass}}{\text{Molar mass}}$      ....(1)

Given mass of oxygen = 50 g

Molar mass of oxygen = 32.00 g/mol

Putting values in equation 1, we get:

$\text{Moles of oxygen}=\frac{50g}{32g/mol}=1.5625mol$

For the given chemical equation:

$2H_2O\rightarrow 2H_2+O_2$

By Stoichiometry of the reaction:

1 mole of oxygen is produced when 2 moles of water is reacted.

So, 1.5625 moles of oxygen is produced when = $\frac{2}{1}\times 1.5625=3.125mol$ of water is reacted.

To calculate the mass of water, we use equation 1:

Moles of water = 3.125 moles

Molar mass of water = 18.01 g/mol

Putting values in equation 1, we get:

$3.125mol=\frac{\text{Mass of water}}{18.01g/mol}\\\\\text{Mass of water}=56.28g$

Hence, the mass of water that must be reacted is 56.28 grams.