Hydrates
1.
Cupric chloride, CuCl
CuCl
2
.
x H
2
, when heated to 100°C is dehydrated. If 0.235g of
O gives 0.185g of CuCl
2
on heating, what is the value of x? What is its name?
2
2.
If “Epsom Salt,” MgSO
4
.
xH
2
O is heated to 250°C, all the water of hydration is lost.
On heating a 1.687 g sample of the hydrate, 0.824 g of MgSO
4
remains. What is the formula of the hydrate? What is its name?
(MgSO
4
.
7H
2
O; magnesium sulfate heptahydrate)
Combustion Analysis/% Composition
3.
A 0.537 g sample of a substance containing only carbon, hydrogen, and oxygen was burned in air to produce 1.030 g of CO
2
and 0.632 g of H
2
O. What is the empirical formula of the substance? What is the percent composition of the original substance?

4.
What is the percent composition by mass of the following compounds: a.
b.
Calcium carbonate
Copper (II) oxide c.
Magnesium hydroxide
(40.0% Ca, 12.0% C, 48.0 %O)
(79.9% Cu, 20.1% O)
5.
A sample of iron oxide contains 70% Fe and 30%O. What is the mass of Fe in 137g of the iron oxide? (95.9g)
6.
Suppose you dig up a copper ore and 85.0% of it is the copper (II) oxide from question 4b. a.
If you have 750 kg of this copper ore, how much of it is copper (II) oxide? b.
How much copper metal could be recovered from this 750 kg of ore?
7.
The makers of “Citrical” (calcium citrate) claim their calcium is “better absorbed” than the calcium from Tums. If you assume a 750 mg tablet is 60% calcium citrate
(the rest is sugar, starch, etc.), what mass of calcium do you get from 3 of these tablets? (The citrate ion is C
6
(24.1% Ca, 325mg Ca)
H
5
O
73-
; determine the formula and the % calcium first).

Empirical and Molecular Formulas
8.
An ionic compound is 44.8%K, 18.4%S, and 36.8%O. What is the empirical formula and the name of the compound? (Hint: check list of polyatomic ions) (K potassium sulfate)
2
SO
4
;
9.
You are called to investigate a murder. You analyze the substance found at the site and find its percent composition is 40.0%C, 6.6%H, and 53.4%O. You analyze further to find its actual molar mass = 180 g/mol. What is the molecular formula for this compound? (C
6
H
12
O
6
)
10.
You analyze some iron ore for your mining company. You recover 35.0g of iron from 50.0g of an iron oxide. What is the empirical formula and NAME for this iron oxide (i.e. what is its Roman numeral?) (Fe
2
O
3
; iron (III) oxide)
11.
What is the empirical formula for a compound that is 43.4%C, 1.2%H, 38.6%O, and
16.9%N?

12.
A compound made from nitrogen and oxygen is found to be 74.1% oxygen. Find the empirical formula. List three possible molecular formulas for this compound.
13.
How many nitrogen atoms are in 59.0g of ammonium phosphate?
14.
The compound methyl butanoate (an ester) smells like apples. It’s percent composition is: 58.8%C, 9.9%H, and 31.3%O. If its molar mass is 306 g/mole, what is the molecular formula?
15.
A forensic scientist is given a white substance that is thought to be cocaine. The substance is found to have the following percent composition: 49.48%C, 5.19%H,
28.85%N, and 16.48% O. What is the empirical formula for this substance? Is the substance cocaine? (The formula for cocaine is C
17
H
2
NO
4
)

General Mole Conversions with Atoms and Molecules
16.
How many molecules are there in 24 grams of FeF
3
?
17.
How many grams are there in 2.3 x 10 24 atoms of silver?