Study Guide: Moles and stoichiometry practice problems Concept of mole/molar ratio
1) How many moles of sodium atoms correspond to 1.56 x 10 21 atoms of sodium?
2) How many moles of Al atoms are needed to combine with 1.58 mol of O atoms to make aluminum oxide,
Al 2 O 3 ?
3) How many moles of Al are in 2.16 mol of Al 2 O 3 ?
4) Aluminum sulfate, Al 2 (SO 4 ) 3 , is a compound used in sewage treatment plants.

a. Construct a pair of conversion factors that relate moles of aluminum to moles of sulfur for this
compound
b. Construct a pair of conversion factors that relate moles of sulfur to moles of Al 2 (SO 4 ) 3
c. How many moles of Al are in a sample of this compound if the sample also contains 0.900 mol
S?
d. How many moles of S are in 1.16 mol Al 2 (SO 4 ) 3 ?

5) How many moles of H 2 and N 2 can be formed by the decomposition of 0.145 mol of ammonia, NH 3 ?
6) What is the total number of atoms in 0.260 mol of glucose, C 6 H 12 O 6 ?
7) What is the mass of 1.00 mol of each of the following elements?

a. Sodium b. Sulfur c. Chlorine
8) Determine the mass in grams of each of the following:

a. 1.35 mol Fe b. 24.5 mol O c. 0.876 mol Ca d. 1.25 mol Ca 3 (PO 4 ) 2
e. 0.625 mol Fe(NO 3 ) 3 f. 0.600 mol C 4 H 10 g. 1.45 mol (NH 4 ) 2 CO 3

9) Calculate the number of moles of each compound:

a. 21.5 g CaCO 3 b. 1.56 g NH 3 c. 16.8 g Sr(NO 3 ) 2 d. 6.98 g Na 2 CrO 4

Percent composition and empirical formulas
10) Calculate the percentage composition by mass of each element in the following compounds:

a. NaH 2 PO 4 b. NH 4 H 2 PO 4 c. (CH 3 ) 2 CO

Balancing equations 11)Write the equation that expresses in acceptable chemical shorthand the following
statement: “Iron can be made to react with molecular oxygen (O 2 ) to give iron oxide with the formula Fe 2 O 3 ”

12) Balance the following reactions:
a. Ca(OH) 2 + HCl  CaCl 2 + H 2 O
b. AgNO 3 + CaCl 2  Ca(NO 3 ) 2 +AgCl
c. Fe 2 O 3 + C  Fe + CO 2
d. NaHCO 3 + H 2 SO 4  Na 2 SO 4 + H 2 O + CO 2
e. C 4 H 10 + O 2  CO 2 +H 2 O
f. Mg(OH) 2 + HBr  MgBr 2 + H 2 O
g. Al 2 O 3 + H 2 SO 4  Al 2 (SO 4 ) 3 + H 2 O
h. KHCO 3 + H 3 PO 4  K 2 HPO 4 + H 2 O + CO 2
i. C 9 H 10 O + O 2  CO 2 + H 2 O

Stoichiometry
13) Chlorine is used by textile manufacturers to bleach cloth. Excess chlorine is destroyed by its reaction with
sodium thiosulfate, Na 2 S 2 O 3 :

Na 2 S 2 O 3(aq) + 4Cl 2(g) + 5H 2 O (aq)  2NaHSO 4(aq) + 8HCl (aq)
a. How many moles of Na 2 S 2 O 3 are needed to react with 0.12mol of Cl 2 ?
b. How many moles of HCl can form from 0.12mol of Cl 2 ?
c. How many moles of H 2 O are required for the reaction of 0.12mol of Cl 2 ?
d. How many moles of H 2 O react if 0.24mol HCl is formed?

14) The incandescent white of a fireworks display is caused by the reaction of phosphorous with O 2 to give
P 4 O 10 .
a. Write the balanced chemical equation for the reaction.
b. How many grams of O 2 are needed to combine with 6.85g of P?
c. How many grams of P 4 O 10 can be made from 8.00g of O 2 ?
d. How many grams of P are needed to make 7.46g P 4 O 10 ?

15) In dilute nitric acid, HNO 3 , copper metal dissolves according to the following equation:

3Cu (s) + 8HNO 3(aq)  3Cu(NO 3 ) 2(aq) + 2NO (g) + 4H 2 O (aq)
How many grams of HNO 3 are needed to dissolve 11.45g of Cu?