Determine the mass fraction of substances in the solution obtained as a result of successive dissolution

Determine the mass fraction of substances in the solution obtained as a result of successive dissolution in 150 ml. water 5.75g. sodium and 8.1 g. zinc oxide.

Given:
V (H2O) = 150 ml
m (Na) = 5.75 g
m (ZnO) = 8.1 g

Find:
ω (products) -?

1) 2Na + 2H2O => 2NaOH + H2 ↑;
ZnO + 2NaOH + H2O => Na2 [Zn (OH) 4];
2) m (H2O) = ρ * V = 1 * 150 = 150 g;
3) n (Na) = m / M = 5.75 / 23 = 0.25 mol;
4) n total (NaOH) = n (Na) = 0.25 mol;
5) n (ZnO) = m / M = 8.1 / 81 = 0.1 mol;
6) n (Na2 [Zn (OH) 4]) = n (ZnO) = 0.1 mol;
7) m (Na2 [Zn (OH) 4]) = n * M = 0.1 * 179 = 17.9 g;
8) n react. (NaOH) = n (ZnO) * 2 = 0.1 * 2 = 0.2 mol;
9) n rest. (NaOH) = n total (NaOH) – n re. (NaOH) = 0.25 – 0.2 = 0.05 mol;
10) m rest. (NaOH) = n rest. * M = 0.05 * 40 = 2 g;
11) n (H2) = n (Na) / 2 = 0.25 / 2 = 0.125 mol;
12) m (H2) = n * M = 0.125 * 2 = 0.25 g;
13) m solution = m (H2O) + m (Na) + m (ZnO) – m (H2) = 150 + 5.75 + 8.1 – 0.25 = 163.6 g;
14) ω rest. (NaOH) = m rest. * 100% / m solution = 2 * 100% / 163.6 = 1.22%;
15) ω (Na2 [Zn (OH) 4]) = m * 100% / m solution = 17.9 * 100% / 163.6 = 10.94%.

Answer: The mass fraction of NaOH is 1.22%; Na2 [Zn (OH) 4] – 10.94%.

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