CHEM 5013 - Applied Chemical Principles
Suggested problems for Quiz on Thursday October 24
1. Calculate the molar mass of each of the following to 3 significant figures:
a. Ammonium Phosphate
(NH4)3PO4 = (3 x 14.0) + (12 x 1.00) + 31.0 + (4 x 16.0) = 149 g/mole
b. Cobalt (II) Chlorate
Co(ClO3)2 = 58.9 + (2 x 35.5) + (6 x 16.0) = 226 g/mole
c. Iodine Tetrachloride
ICl4 = 127 + (4 x 35.5) = 269 g/mole
2. How many atoms and moles of atoms (or ions) are in one mole of each of the following
compounds?
a. Magnesium Chloride
MgCl2
One mole of MgCl2 contains 1 mole of Magnesium ions (6.02 x 1023
Magnesium ions) and 2 moles of Chloride ions (12.04 x 1023 Chloride ions)
b. Ammonium Hydroxide NH4OH
One mole of NH4OH contains 1 mole of Ammonium ions (6.02 x 1023
Ammonium ions) and 1 mole of Hydroxide ions (6.02 x 1023 Hydroxide
ions). OR One mole of NH4OH contains 1 mole of nitrogen atoms (6.02 x
1023 Nitrogen atoms), 5 moles of Hydrogen atoms (30.1 x 1023) Hydrogen
atoms and 1 mole of Oxygen atoms (6.02 x 1023 Oxygen atoms)
c. Oxygen Gas
O2
1 mole of O2 contains 2 moles of oxygen atoms (12.04 x 1023 Oxygen
atoms)
3. What is the mass in grams for each of the following?
a. 5.00 moles of Silver Phosphate Ag3PO4 = 418.7 g/mole
5.00 moles x 418.7 grams
1 mole
=
2094 grams
b. 7.50 moles of Diphosphorus Pentoxide P2O5 = 142 g/mole
7.50 moles x 142 grams
1 mole
=
1065 grams
4. a. How many atoms are in 4.55 moles of aluminum metal?
6.02 x 1023 atoms x 4.55 moles
1 mole
=
2.74 x 1024 atoms
b. How many atoms are in 4.55 moles of copper metal?
Same calculation as 4a. It does not matter what the material is, 4.55 moles of
any element contains 2.74 x 1024atoms!!!
c. How many atoms are in 4.55 moles of hydrogen gas (remember it is a molecule!)?
2.74 x 1024 atoms x
2 H atoms
1 H molecule
=
5.84 x 1024 atoms
d. How many molecules are in 4.55 moles of hydrogen gas?
Same calculation as 4a. 4.55 moles of Hydrogen gas contains 2.74 x 1024
molecules of Hydrogen!!
5. A 175.5 gram sample of water contains how many water molecules?
175.5 g x 1 mole = 9.75 moles H2O x 6.02 x 1023 molecules = 5.87 x 1024 molecules
18.0 g
1 mole
6. You have a sample that contains 5.75 x 1035 molecules of water.
a. How many moles of water is this sample?
5.75 x 1035 molecules x
1 mole
=
23
6.02 x 10 molecules
9.55 x 1011 moles
b. What is the mass in grams of this water sample?
9.55 x 1011 moles x 18 grams
1 mole
=
1.72 x 1013 grams
7. How many moles are present in each of the following amounts:
a. 34 grams of Copper (II) Sulfate
CuSO4 = 159.5 g/mole
34 g x 1 mole
159.5 g
=
0.213 mole
b. 75 grams of Sulfur Dioxide
SO2 = 64 g/mole
75 g x 1 mole
64 g
=
1.17 moles
8. What is the mass in grams of 5.00 x 1023 atoms of Gold?
5.00 x 1023 atoms x
1 mole
= 0.831 moles Au x 197 grams = 163.6 g
6.02 x 1023 atoms
1 mole
FYI – This would have a value of $7,606 at current market value of $1318 per
ounce of gold!!!
9. The active ingredient of some shampoos ammonium lauryl sulfate. The molecular formula
of this compound is CH3(CH2)11OSO3NH4. Calculate the mass percent of each element in
this ingredient (the percent composition).
Molar Mass = (12x12g/mol)+(29x1g/mol)+(4x16g/mol)+14g/mol+32g/mol = 283g/mol
%C = (12x12g/mol) x 100 = 50.9%
283 g/mol
%S=
32g/mol x 100 = 11.3%
283 g/mol
%H = (29x1g/mol)
283 g/mol
x 100 = 10.2%
%N=
14 g/mol x 100 = 4.9%
283 g/mol
%O = (4x16g/mol)
283 g/mol
x 100 = 22.6%
10. NutraSweet has the following percent composition by mass: 57.14%C, 6.16%H, 9.52% N,
and 27.18%O.
a. What is the empirical formula of NutraSweet?
(Assume 100 grams total mass), then
Moles C = 57.14 grams x 1 mole = 4.76 moles C
12 g
Moles H = 6.16 grams x 1 mole = 6.16 moles H
1g
Moles N = 9.52 grams x 1 mole = 0.68 moles N
14 g
Moles O = 27.18 grams x 1 mole = 1.70 moles O
16 g
The divide all subscripts by 0.68 to give  C7H9N1O2.5
Finally, multiply by 2 to give whole number subscripts  C14H18N2O5
b. What is the molecular formula of NutraSweet if the molecular weight is 294 amu?
Empirical Formula weight = (14x12g/mol)+(18x1g/mol)+(2x14g/mol)+(5x16g/mol)
= 294 g/mol thus, Molecular form. equals empirical form.