Question

how much hydrogen in grams could be obtained from 4.5L of water?

Answer 1

How much hydrogen in grams could be obtained from 4.5L of water?

Solution

Water volume $V(H_2O) = 4.5L$

Water density $\rho(H_2O) = 1\,\mathrm{kg}\bullet\mathrm{L}^{-4}$

Water molar mass $M_r(H_2O) = 0.018\,\mathrm{kg}\bullet\mathrm{mol}^{-1}$

Hydrogen production

$$\begin{array}{l} 2H_2O \xrightarrow{\text{electrolysis}} 2H_2\uparrow + O_2\uparrow \\ 2H^1 + 2e^- = H_2^0 \\ 2O^{-2} - 4e^- = O_2^0 \\ \end{array}$$

Based on the reaction equation $n(H_2O) = n(H_2)$

n – Number of moles

$$\begin{array}{l} n(H_2O) = n(H_2) = \frac{m(H_2O)}{M_r(H_2O)} = \frac{V(H_2O)}{V(H_2O)} \cdot \frac{\rho(H_2O)}{M_r(H_2O)} = \\ 4.5(L) \cdot 1\,\mathrm{kg}\bullet\mathrm{L}^{-4} \quad /0.018\,\mathrm{kg}\bullet\mathrm{mol}^{-1} = 250\,\mathrm{mol} \\ \end{array}$$

Find hydrogen mass

$$m(H_2) = M_r(H_2) \cdot n(H_2) = 2(g \cdot \mathrm{mol}^{-1}) \cdot 250\,\mathrm{mol} = 500\,\mathrm{g}$$

**Answer**: 500g of hydrogen could be obtained from 4.5 L of water