Chemistry 2AChemistry 2A-c w2009 c w2009 (Ch3(Ch3-5)315)31Example: Given that a compound contains 44.9% K, 18.4% S, and 36.7% O by weight, calculate the empirical formula.Solution: # mol K = 44.9 g/(39.1 g/mol)=1.148 mol# mol S = 18.4 g/(32.066 g/mol)=0.574 mol# mol O = 36.7 g/(15.999 g/mol)=2.294 molThe empirical formula is K2SO4.III. % Composition and chemical formulaExample: Given that a compound has the following % composition: 78.16% B and 21.84% H, calculate the empirical formula. If the molecular weight of this compound is 27.67 amu, what is the molecular formula?Solution: # mol B = 78.16 g/(10.811 g/mol)=7.23 mol# mol H = 21.84 g/(1.008 g/mol)=21.67 molEmpirical formula BH3; formula weight = (10.811 + 3x1.008) amu =13.835 amuMolecular formula = B2H6
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