Silicon was placed in the sodium hydroxide solution. Evolution of 56 liters of hydrogen occurred.

Silicon was placed in the sodium hydroxide solution. Evolution of 56 liters of hydrogen occurred. Determine the mass of the alkali solution consumed for the reaction if the mass fraction of NaOH in it was 20%.

1. Let’s write down the equality of chemical interaction:

2NaOH + Si + H2O = Na2SiO3 + 2H2.

2. Find the chemical amount of hydrogen (Vm – molar volume, constant equal to 22.4 l / mol):

n (H2) = V (H2) / Vm = 56 L / 22.4 L / mol = 2.5 mol.

3. Using the equality of chemical interaction, we find the chemical amount and, as a result, the mass of sodium hydroxide:

n (NaOH) = n (H2) = 2.5 mol.

m (NaOH) = n (NaOH) * M (NaOH) = 2.5 mol * 40 g / mol = 100 g.

4. Find the mass of the sodium hydroxide solution:

m (solution) = m (NaOH) * 100% / ω (NaOH) = 100 g * 100% / 20% = 500 g.

Answer: m (solution) = 500 g.