Theoretical Yield – amount of product that is predicted using stoichiometry

Actual Yield – amount of product that is obtained in an experiment

Percent Yield – compares the mass of product obtained by experiment with the mass of product determined by stoichiometric calculations

Reasons For Low Yield

1. Sources of error. (Experimental procedures)

2. Impurities in reagents used (different grades of chemicals)

3. Side reactions (other products formed)

4. Reactions are reversible

Reasons for High Yield

1. Sources of error (experimental procedures)

Solving Percent Yield Problems

• First, determine the theoretical yield (how much you should get) using stoichiometry

• Second using the experimental/ actual yield, use the formula.

% yield = Experimental yield x 100% theoretical yield

Example 1: In a particular experiment 10.0 g of sugar should be produced but only 0.664 g is produced. What is the percentage yield?

% yield = x 100

= x 100 = 6.64 %

Experimental yield theoretical yield

0.664 g 10.0g

Example 2: Aluminium reacts with oxygen to form aluminium oxide. If 635g of Aluminium

oxide is obtained from reacting 1150g of aluminium, what is the percentage yield?

• Al + O2 Al2O3

• 4Al + 3O2 2Al2O3

Step 1: Write out the balanced chemical equation

• Step 2: Fill in chart with information you know

Balanced

Equation4Al 3O2

2Al2O3

Mole Ratio

4 3 2

Mass (m) 1150gMolar Mass (M)

26.98g/mol

Moles (n)

Step 3: Convert given mass into moles (n=m/M)

= 42.59 mol of Al

Moles of Al = 1150g

27.0g/mol

Part 1: Find the theoretical yield through stoichmetry (how much you should have got)

Fill in chart with information you know

Balanced

Equation4Al 3O2

2Al2O3

Mole Ratio

4 3 2

Mass (m) 1150gMolar Mass (M)

26.98g/mol

Moles (n) 42.59 mol

Step 4: Use moles of given substance to find moles of required substance (mole to mole ratio)

4Al + 3O2 2Al2O3 x mols of Al2O3 = 2 mol of Al2O3 42.59 mol of Al 4mol of Al

42.59 mols of Al 2 mol of Al2O3

4 mol Al

or

X

= 21.31 mols of Al2O3

= 21.31 mols of Al2O3

Fill in chart with information you know

Balanced

Equation4Al 3O2

2Al2O3

Mole Ratio

4 3 2

Mass (m) 1150gMolar Mass (M)

26.98g/mol 102g/mol

Moles (n) 42.59 mol

21.31 mol

Step 5: Convert moles of required substance to the mass (m=n x M)

mass of Al2O3 = 21.31 mol of Al2O3 X 102g/mol

= 2173 g of Al2O3

This is your theoretical yield

Part 2: Calculate Percent Yield

% yield = x 100

= x 100 = 29.2 %

Experimental yield theoretical yield

635 g 2173g

Step 6: Using experimental and theoretical yield find percent yield

Iron (III) oxide reacts with carbon monoxide to produce carbon dioxide and iron. If 300g of iron is produced when 425 of iron ore is used. What is the percentage yield?

Step 1: Write out the balanced chemical equation

Fe2O3 + 3CO 2Fe + 3CO2

m= 425g m= ?

Example 3:

• Step 2: Fill in chart with information you know

Balanced

EquationFe2O3 3CO 2Fe 3CO2

Mole Ratio

1 3 2 3

Mass (m) 425g ? g

Molar Mass (M)

159.7 g/mol

Moles (n)

Step 3: Convert given mass into moles (n=m/M)

Moles of Fe2O3 = 425g

159.7g/mol= 2.66 mol of Fe2O3

Part 1: Find the theoretical yield through stoichmetry (how much you should have got)

• Fill in chart with information

Balanced

EquationFe2O3 3CO 2Fe 3CO2

Mole Ratio

1 3 2 3

Mass (m) 425g ? g

Molar Mass (M)

159.7 g/mol

Moles (n) 2.66mol

Step 4: Calculate the number of mols of the required substance (mol to mole ratio)

Fe2O3 + 3CO 2Fe + 3CO2

x mols of Fe = 2 mol of Fe 2.66 mols of Fe2O3 1mol of Fe2O3

2.66 mols of Fe2O3 2 mol of Fe

1 mols Fe2O3

or

X

= 5.32 mols of Fe

= 5.32 mols of Fe

• Fill in chart with information

Balanced

EquationFe2O3 3CO 2Fe 3CO2

Mole Ratio

1 3 2 3

Mass (m) 425g ? g

Molar Mass (M)

159.7 g/mol

55.85 g/mol

Moles (n) 2.66mol 5.32 mol

Step 5: Convert moles of required substance to the mass

mass of Fe = 5.32 mols of Fe X 55.85g/mol of Fe

= 297g of Fe

Part 2: use percent yield formula

% yield = x 100

= x 100 = 101 %

Experimental yield theoretical yield

300 g 297g

Step 6: Using experimental and theoretical yield find percent yield