The equation of reaction between potassium and water.
2K + 2H[sub]2[/sub]O(1) --> 2KOH(aq) + H[sub]2 [/sub]
Find the mass of potassium needed to produce 1.505 x 10[sup]24[/sup] hydorgen molecule.
Let's find the amount of moles of H2: 1.505x1024/6.022 x 1023 = 2.5 mol. From the ballanced equation 2K + 2H2O(1) -> 2KOH(aq) + H2 we can see that potassium has twice mol than H2. v(H2) = 5 mol. The mass of the potassium is 39 g/mol/ * 5 mol = 195 g.