1. Find the percent composition of the following compounds:
a) KClO3
b) calcium hydroxide
2. Find the empirical formula of the following compounds:
a) a compound which is 41.3% C, 10.4% H, and 48.2% N.
b) a compound containing 1.92 grams of Mn and 1.12 grams of oxygen.
c) a compound which is 65.1% Cu, 32.8% O and 2.1% H. Also name the compound.
d) sample of amino acid glycine contains 1.56 g C, 0.333 g H, 2.08 g O, and 0.910 g N.
3. A hydrocarbon fuel is fully combusted with 18.214 g of oxygen to yield 23.118 g of carbon dioxide and
4.729 g of water. Find the empirical formula for the hydrocarbon.
4. After combustion with excess oxygen, a 12.501 g of a petroleum compound produced 38.196 g of carbon
dioxide and 18.752 of water. A previous analysis determined that the compound does not contain oxygen.
Establish the empirical formula of the compound.
5. In the course of the combustion analysis of an unknown compound, 12.923 g of carbon dioxide, 6.608 g of
water and 2.057 g of nitrogen was measured. The complete combustion of 11.014 g of the compound needed
10.573 g of oxygen. What the compound’s empirical formula?
6. 12.915 g of a biochemical substance was burned in an atmosphere of 50.123 g of oxygen. Subsequent
analysis of the gaseous result yielded 18.942 g carbon dioxide, 7.749 g of water and 36.347 g of oxygen.
Determine the empirical formula of the substance.
7. 33.658 g of oxygen was used to completely react with a sample of a hydrocarbon in a combustion reaction.
The reaction products were 33.057 g of carbon dioxide and 10.816 g of water. Ascertain the empirical formula
of the compound.
1. a) 1 mole KClO3 = (39.1 g K) + (35.4 g Cl) + (3 x 16.0 = 48.0 g O) = 122.5 g
% K = 39.1/122.5 = 31.9% K;
% Cl = 35.4/122.5 = 28.9 % Cl;
% O = 48.0/122.5 = 39.2% O
b) calcium hydroxide = Ca(OH)2
1 mole Ca(OH)2 = (40.08 g Ca) + (2 x 16.0 = 32.0 g O) + (2 x 1.008 = 2.02 g H) = 74.1 g
% Ca = 40.08/74.1 = 54.1% Ca;
% O = 32.0/74.1 = 43.2% O;
% H = 2.02/74.1 = 2.73% H
2.
a) In 100 g of the compound:
41.3 g C x (1 mol C/12.0 g C) =
3.44 mol C
10.4 g H x (1 mol H/1.01 g H) =
10.4 mol H
48.2 g N x (1 mol N/14.0 g N) = 3.44 mol N
Ratio: C: 3.44/3.44 = 1; H: 10.4/3.44 = 3; N: 3.44/3.44 = 1;
CH3N
b) In 100 g of the compound:
1.92 g x (1 mol Mn/54.9 g) = 0.350 mol Mn
1.12 g x (1 mol O/16.0 g) = 0.700 mol O
Ratio: Mn: 0.0350/0.0350 = 1; O: 0.0700/0.0350 = 2;
MnO2
c) In 100 g of the compound:
65.1 g Cu x (1 mol Cu/63.5 g C) = 1.03 mol Cu
32.8 g O x (1 mol O/16.0 g O) = 2.05 mol O
2.1 g H x (1 mol H/1.0 g H) = 2.1 mol H
Ratio: Cu: 1.03/1.03 = 1; O: 2.05/1.03 = 2; N: 2.1/1.03 = 2;
Cu(OH)2 (it contains copper, so it's ionic) name = copper(II) hydroxide
d) In 100 g of the compound:
1.56 g C x (1 mol C/12.0 g C) = 0.130 mol C
0.333 g H x (1 mol H/1.01 g H) = 0.333 mol H
2.08 g O x (1 mol O/16.0 g O) = 0.130 mol O
0.910 g N x (1 mol N/14.0 g N) = 0.0650 mol N
Ratio: C: 0.130 /0.0650 = 2; H: 0.333/0.0650 = 5; O: 0.130 /0.0650 = 2;
N: 0.0650 /0.0650 = 1;
C2H5O2N
3. A hydrocarbon fuel is fully combusted with 18.214 g of oxygen to yield 23.118 g of carbon dioxide and
4.729 g of water. Find the empirical formula for the hydrocarbon.
4. After combustion with excess oxygen, a 12.501 g of a petroleum compound produced 38.196 g of carbon
dioxide and 18.752 of water. A previous analysis determined that the compound does not contain oxygen.
Establish the empirical formula of the compound.
5. In the course of the combustion analysis of an unknown compound, 12.923 g of carbon dioxide, 6.608 g of
water and 2.057 g of nitrogen was measured. The complete combustion of 11.014 g of the compound needed
10.573 g of oxygen. What the compound’s empirical formula?
6. 12.915 g of a biochemical substance was burned in an atmosphere of 50.123 g of oxygen. Subsequent
analysis of the gaseous result yielded 18.942 g carbon dioxide, 7.749 g of water and 36.347 g of oxygen.
Determine the empirical formula of the substance.
7. 33.658 g of oxygen was used to completely react with a sample of a hydrocarbon in a combustion reaction.
The reaction products were 33.057 g of carbon dioxide and 10.816 g of water. Ascertain the empirical formula
of the compound.