How much hydrogen sulfide is required for the reaction with 28 g of KOH.

Reaction equation: 2KOH + H2S = K2S + 2H2O
According to the periodic table, we determine the molar mass of potassium hydroxide M = 39 + 16 + 1 = 56 g / mol.
Find the amount of potassium hydroxide substance n = m / M = 28 g / 56 g / mol = 0.5 mol.
By reaction with 2 mol of hydroxide, 1 mol of hydrogen sulfide reacts, which means 0.5 / 2 = n (H2S) / 1. n (H2S) = 0.25 mol.
Let us find the volume of hydrogen sulfide V = n * Vm, where Vm = 22.4 l / mol is the molar volume, a constant value for all gases under normal conditions. V (H2S) = 0.25 mol * 22.4 L / mol = 5.6 L.