\(2 \ H_2 + O_2 \to 2 \ H_2O\)
2 moles of H₂ : 1 mole of O₂ : 2 moles of H₂O
number of moles of H₂ : number of moles of H₂O = 1 : 1
\(m_{H_2}=10 \ g \\
M_{H_2}=2 \ \frac{g}{mol} \\
n_{H_2}=\frac{10 \ g}{2 \frac{g}{mol}}=5 \ mol\)
There are 5 moles of hydrogen so there must be 5 moles of water too.
\(n_{H_2O}=5 \ mol \\
M_{H_2O}=18 \ \frac{g}{mol} \\
m_{H_2O}=5 \ mol \times 18 \ \frac{g}{mol}=90 \ g\)
The mass of H₂O is 90 g.
