Question

2NaCl + 2H2O -> 2NaOH + H2 + Cl2
What mass of NaCl would be required to produce 120dm^3 of hydrogen?
What mass of sodium hydroxide would be produced if 120dm^2 of H2 is produced?

Answer 1

First convert 120 cubic decimeter of hydrogen to mol hydrogen.
First you need to know what 1 mole of (every) gas occupies 22.4 L
120 cubic dm = 120 liter (cubic decimeters is the same as liter)
120 L divided by 22.4 L = 5.36 mol H2

The reaction ratio is 2:2;2:1:1
2 mol NaCl reacts with 2 moles of water to produce 2 mole NaOH, 1 mol H2 and 1 mol Cl2.
So when 5.36 moles of H2 are produced, the reaction needed 10.72 moles of NaCl.

Now you calculate the mass of 10.72 mol NaCl.
The molar mass of NaCl = 58.443 g/mol
10.72 * 58.443 = 626.509 gram NaCl

For the NaOH part:
according to the ratio, if 1 mol of H2 is produced, 2 mol of NaOH is produced.
So when 5.36 mol H2 is produced, the reaction produces 10.72 mol NaOH
Calculate the mass of 10.72 mol NaOH
The molar mass of NaOH = 39.997 g/mol
10.72 * 39.997 = 428.768 gram NaOH