Chapter 9 Problems a, 9.18 b and 9.38 a

Citric acid with a molecular mass 192 amu Mass %: C 37.50, H 4.21 and O Determine molecular formula starting from g citric acid How many moles of each in g? C: g x g x 1 mole = g12.01 g H: g x 4.21 g x 1 mole = g1.01 g

Citric acid with a molecular mass 192 amu – cont’d O: g x g x 1 mole = g16.00 g Empirical formula C: 3.125/3.125 = 1 H: 4.17/3.125 = 1.33 O: 3.643/3.125 = What is the multiplier? 6

Citric acid with a molecular mass 192 amu – cont’d C6HxOyC6HxOyC6HxOyC6HxOy x = 1.33 * 6 = 7.98 y = * 6 = C6H8O7C6H8O7C6H8O7C6H8O7 This is the …..

Citric acid with a molecular mass 192 amu – cont’d Empirical formula Empirical formula mass is … 6 * * * = amu What is the molecular formula? Same as empirical formula

Citric acid C 6 H 8 O 7 Going Backward Knowing the formula, can we calculate % mass composition? Does it matter if we have empirical or molecular formula?

Problem 9.18 b) % composition of Na in NaCN Na: 1 * = amu C: 1 * = amu N: 1 * = amu Total = amu %Na by mass = (22.99/49.01) * 100 = %

Problem 9.38 a) Mass in grams of mole of SO 2 S: 1 * = O: 2 * = Sum = mole * (64.06 g/1mole) = g Significant figures? How many molecules of SO 2 in mole?