In 3.3 moles of potassium sulphide (K2S), there are 363.99 g. Let's first calculate the molar mass of K2S (Mr) which is the sum of atomic masses (Ar) of its elements. According to the periodic table, Ar(K) = 39.1 g/mol and Ar(S) = 32.1 g/mol. Mr(K2S) = 2Ar(K) + Ar(S) = 2 * 39.1 + 32.1 = 110.3 g/mol. Thus, there are 110.3 g per 1 mol. There will be x grams in 3.3 moles. 110.3 g : 1 mol = x : 3.3 mol. x = 110.3 g * 3.3 mol : 1 mol = 363.99 g.
