Mass-Mass Problems
SOLVING STOICHIOMETRY PROBLEMS
TYPES OF STOICHIOMETRY PROBLEMS
Major categories of stoichiometry problems are:
1.) mass-mass problems
2.) mass-volume problems
3.) volume-volume problems
STOICHIOMETRY
MASS A
VOLUME A
MOL “A”
MASS B
VOLUME B
MOL “B”
SOLVING MASS-MASS PROBLEMS
In a mass-mass problem, you are given the mass
of one substance and are asked to find the mass
of another substance.
STEP 1:
Convert the given mass to moles using molar mass
of given.
Given mass of substance “A” ÷ molar mass of substance “A” = Mol “A”
STEP 2:
Determine the number of moles for the
unknown by using molar ratio of the
coefficients in the balanced equation.
Mol “A” x molar ratio “B” = Mol “B”
“A”
STEP 3:
Convert the number of moles for the unknown
into grams using molar mass of the unknown.
Mol “B” x molar mass of unknown = Mass “B”
EXAMPLE
The average person drinks 2 L of water each day, yet
eliminates about 2.5 L. Where do you think the
extra water comes from? It is produced when food
is metabolized in the body. Metabolism is the sum
of all the chemical reactions that occur in the body.
In one series of reactions, glucose (C6H12O6) is
burned in oxygen to produce carbon dioxide and
water. What mass of water is produced from 1.5 g
of glucose? The balanced equation for this reaction
is:
C6H12O6 + 6O2  6CO2 + 6H2O
CALCULATE THE MOLAR MASS OF THE GIVEN
SUBSTANCE: C6H12O6
Molar mass: C = 6 x 12 = 72
C6H12O6
H = 12 x 1 = 12
O = 6 x 16 = 96
180 g/mol
CONVERT GRAMS OF GLUCOSE (C6H12O6) TO
MOLES OF WATER (H2O).
1.5 g C6H12O6
180 g/mol C6H12O6
0.0083 molC6H12O6 x
6 H2O = 0.050 molH2O
1 C6H12O6
CALCULATE MOLAR MASS OF UNKNOWN
SUBSTANCE: H2O
Molar mass: H = 2 x 1 = 2
H2O
O = 1 x 16 = 16
18g/mol
CONVERT MOLES OF WATER (H2O) TO GRAMS OF
WATER (H2O).
0.090 g H2O
0.050mol x 18g/mol
PRACTICE PROBLEMS
1. In a thermite reaction, powdered aluminum
reacts with iron (III) oxide to produce aluminum
oxide and molten iron. What mass of aluminum
oxide is produced when 2.3 g of aluminum
reacts with iron (III) oxide? The balanced
equation is: 2Al + Fe2O3  2Fe + Al2O3
2. Determine the mass of sodium hydroxide
produced when 0.25g of sodium reacts with
water according to the following equation:
2Na + 2H2O  2NaOH + H2
3. What mass of bromine (Br2) is produced
when fluorine reacts with 1.72 g of
potassium bromide. The balanced equation
is: 2F + 2KBr  2KF + Br2