Let's write the chemical equation:
[tex]2Na+2H_2O\to2NaOH+H_2,[/tex]Using the mass of sodium (Na), we can calculate the number of moles of sodium:
[tex]120g\text{ Na}\cdot\frac{1\text{ mol Na}}{23\text{ g Na}}=5.217\text{ mol Na,}[/tex]2 mol of Na produces 1 mol of hydrogen gas (2 moles because hydrogen gas contains 2 moles).
We can calculate the number of hydrogen moles required like this:
[tex]5.217\text{ mol Na}\cdot\frac{2\text{ mol H}}{2\text{ mol Na}}=5.217molH_2,[/tex]Now, to calculate the mass of hydrogen, we're going to use the molar weight, like this:
[tex]5.217molH_2\cdot\frac{1gH_2}{1\text{ mol }H_2}=5.217gH_2\text{.}[/tex]So, hydrogen will be 5.217 g produced by 120 g of sodium.
