25 g of a mixture of zinc and zinc oxide was treated with a 40% potassium hydroxide solution with a density of 1.39 g / ml, the volume of the evolved gas was 4.48 liters. Determine the volume of the used solution.
Zn + 2KOH + 2H2O → K2 [Zn (OH) 4] + H2
ZnO + 2KOH + H2O → K2 [Zn (OH) 4]
m (mixture) = 25 g
n (H2) = 4.48 / 22.4 = 0.2 mol
m (Zn) = 0.2 x 65 = 13 g
m (ZnO) = 25 – 13 = 12 g
n (ZnO) = 12 / (65 + 16) = 0.15 mol
m (KOH total) = (0.4 + 0.3) x 56 = 39.2 g
m = ω x V x ρ
⇒ 39.2 = 0.4 x 1.39 x V
V = 70.5 ml
Answer: the volume of the consumed solution is 70.5 ml.
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