What mass of potassium should be taken to prepare an aqueous solution of potassium hydroxide weighing 100 g with a mass fraction of 8%.
1. Let’s write down the reaction of obtaining potassium hydroxide:
2K + 2H2O = 2KOH + H2 ↑;
2.Calculate the mass of potassium hydroxide:
m (KOH) = w (KOH) * m (solution) = 0.08 * 100 = 8 g;
3.Calculate the chemical amounts of hydroxide and metal:
n (KOH) = m (KOH): M (KOH);
M (KOH) = 39 + 16 + 1 = 56 g / mol;
n (KOH) = 8: 56 = 0.143 mol;
n (K) = n (KOH) = 0.143 mol;
4.determine the mass of potassium:
m (K) = n (K) * M (K) = 0.143 * 39 = 5.577 g.
Answer: 5.577 g.
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