When an excess of sodium hydroxide solution was reacted with 16 g of silicon, 22.4 liters of hydrogen

When an excess of sodium hydroxide solution was reacted with 16 g of silicon, 22.4 liters of hydrogen were obtained. Calculate the mass fraction of silicon in the sample taken. How many grams of silicon oxide (IV) was in it? How many grams of 60% alkali solution was required for the reaction.

Given:
m tech. (Si) = 16 g
V (H2) = 22.4 L
ω (NaOH) = 60%

To find:
ω (Si) -?
m (SiO2) -?
m solution (NaOH) -?

1) 2NaOH + Si + H2O => Na2SiO3 + 2H2 ↑;
2) n (H2) = V (H2) / Vm = 22.4 / 22.4 = 1 mol;
3) n clean. (Si) = n (H2) / 2 = 1/2 = 0.5 mol;
4) m clean. (Si) = n pure. (Si) * M (Si) = 0.5 * 28 = 14 g;
5) ω (Si) = m pure. (Si) * 100% / m tech. (Si) = 14 * 100% / 16 = 87.5%;
6) m (SiO2) = m tech. (Si) – m pure. (Si) = 16 – 14 = 2 g;
7) n (NaOH) = n (H2) = 1 mol;
8) m (NaOH) = n (NaOH) * M (NaOH) = 1 * 40 = 40 g;
9) m solution (NaOH) = m (NaOH) * 100% / ω (NaOH) = 40 * 100% / 60% = 66.7 g.

Answer: The mass fraction of Si is 87.5%; weight of SiO2 – 2 g; weight of NaOH solution – 66.7 g.