4) How many grams of O2 must react with 983.4 g of carbon to make C6H12O6? 983.4g C x
1 mol C x 12.0g C
1 mol C6H12O6 6 mol C
x
6 mol O x 1 mol C6H12O6
1 mol O2 2 mol O
x
32.0g O2 1 mol O2
=
1311g O2
5) What is the percent composition of each element in ammonium acetate? NH4C2H3O2 = 77.03g/mol %N = (14.0/77.03) x 100% = 18.2% N %H = (7.07/77.03) x 100% = 9.18% H %C = 24.0/77.03 x 100% = 31.2% C %O = 32.0/77.03 x 100% = 41.5% O
6) What is the percent composition of each element in aluminum sulfate? Al2(SO4)3 = 342g/mol %Al = 54.0/342 x 100% = 15.8% Al % S = (32.1 x 3)/342 x 100% = 28.2% S %O = (16 x 7)/342 x 100% = 56.1% O
7) A compound is 26.28% carbon, 3.68% hydrogen, and the rest is oxygen. The molecular weight is 548.32 g/mole. What are the empirical and molecular formulas? 26.28g C x
1 mol C = 12.0g C
70.04g O x
1 mol O 16.0 g O
=
4.38 mol O
3.68 g H
1 mol H 1.01g H
=
3.64 mol H
x
2.19 mol C
Mole Ratio = 2.19 : 3.64 : 4.38 = 3 : 5 : 6 Empirical Formula = C3H5O6 Empirical Forumla Mass = 137.05g/mol 548.32/137.05 = 4, so Molecular Formula = C12H20O24
8) A sample of a compound is decomposed into its constituent elements, to give 150.9 g carbon, 15.87 g hydrogen, and 301.6 g oxygen. The molecular weight is 149.09 g/mole. What are the empirical and molecular formulas? 150.9g C
x 1 mol C 12.0g C
15.87g H x
1 mol H 1.01g H
301.6g O x
1 mol O 16.0g O
= 12.58 mol C = 15.71 mol H =
18.86 mol O
Mole ratio = 12.58 : 15.71 : 18.85 = 4 : 5 : 6 Empirical Formula = C4H5O6 Empirical Formula Mass = 149.05g/mol 149.09/149.05 = 1, so Molecular Formula = C4H5O6
9) A compound is 17.15% carbon, 2.88% hydrogen, and the rest is oxygen. The molecular weight is 280.12 g/mole. What are the empirical and molecular formulas? 17.15 g C x 1 mol C = 1.429 mol C 12.0 g C 79.97 g O x
1 mol O = 4.998 mol O 16.0 g O
2.88 g H
1 mol H = 2.85 mol H 1.01 g H
x
Mole Ratio = 1.429 : 2.85 : 4.998 Empirical Formula = C2H4O7 Empirical Formula Mass = 140.0g/mol 280.12/140.0 = 2, so Molecular Formula = C4H8O14
10) 987.0 g of a gas occupies 168.4 L at STP. What is the molecular weight of the gas? 987.0 g x 168.4 L
22.4 L 1 mol
= 131.3 g/mol
11) A compound, “A3N2” is 91.93% mystery element A, and the rest is nitrogen. What is the atomic weight of A? What is the identity of A? 8.07 g N x