Hello all I encountered the following problems: What is the formula weight of: a. potassium phosphate b. iron(III) oxide c. diphosphorous pentasulfide I know that the formula for (a) is K2S04. Hence I know there are 2K's 1 S and 4 O's. After obtaining the atomic masses, I sum them all up. The answer is 212.3 amu but I dont get this. Any help would be appreciated Thanks!