What is the mass, in grams, of 2.90×10−3 mol of ammonium phosphate?

0.432 g First, calculate the molar mass of ammonium phosphate by looking up the atomic mass of each element in ammonium phosphate Nitrogen = 14.0067 Hydrogen = 1.00794 Oxygen = 15.999 Phosphorus = 30.973762 Each molecule of ammonium phosphate has 3 Nitrogen, 12 Hydrogen, 1 Phosphorus, and 4 Oxygen atoms. Multiply the number of each type of atom with the atomic mass of each type of atom and add the results. m = 3 * 14.0067 + 12 * 1.00794 + 30.973762 + 4 * 15.999 m = 149.0851 So one mole of ammonium phosphate has a mass of 149.0851 g Since you have 2.90x10-3 moles, just multiply by the molar mass m = 2.90x10^-3 * 149.0851 = 0.432347 g Since you only have 3 significant figures for the number of moles, round the result to 3 significant figures giving 0.432 g