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Solving Stoichiometry Problems

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Mass-Mass Problems

Solving 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

MASS B VOLUME B

MOL “A”

MOL “B”

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”

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

Molar mass: C = 6 x 12 = 72

C6H12O6 H = 12 x 1 = 12

O = 6 x 16 = 96

180 g/mol

0.0083 molC6H12O6 x 6 H2O = 0.050 molH2O

1 C6H12O6

1.5 g C6H12O6

180 g/mol C6H12O6

Molar mass: H = 2 x 1 = 2

H2O O = 1 x 16 = 16

18g/mol

0.090 g H2O

0.050mol x 18g/mol

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