To find the answer to this question we need to first have the reaction well balanced, which we already have:
2K + 2 H2O -> 2KOH + H2
Something to notice here is that to form 1 molecule of H2 we need 2 molecules of K, so we have a ratio of 2:1 (K:H2).
Now we have to find out how many moles of K we have in this reaction when we have 6.32g of K, the atomic mass for K is 39.09g/mol:
39.09g = 1 mol
6.32g = x moles
x = 0.16 moles of K
So in this reaction we have 0.16 moles of K, and according to our 2:1 ratio, we have to divide this 0.16 by 2, therefore, 0.16 moles of K means 0.08 moles of H2 in the reaction. Now let's find the mass of H2, the molar mass of H2 is 2.014g/mol
1 mol = 2.014g
0.08 moles = x grams
x = 0.16 grams of H2
