1. Limiting/Excess Reagent Problem
Stacy McFadden Pd. 7

2. Calculate the moles and masses(g) for each chemical in the reaction, if g of Aluminum is reacted with 15.8 g of Lithium Hydroxide

3. Write a complete and balanced equation
Al Li(OH)  3Li Al(OH)3

4. Draw a column for each chemical
Al Li(OH)  3Li Al(OH)3

5. Draw a line to separate the columns into two rows
Al Li(OH)  3Li Al(OH)3

6. Write the amounts given in the appropriate columns
Al Li(OH)  3Li Al(OH)3
12.2 g
15.8 g

7. Convert the amounts given into moles
Convert the amounts given into moles. Since Al has less moles than Li(OH), You only have to worry about the top half
Al Li(OH)  3Li Al(OH)3
12.2 g
12.2g x 1mole g = .452 moles
15.8 g g x 1mole g =.660

8. In each of the other columns write the moles of given (x) a fraction
Al Li(OH)  3Li Al(OH)3
12.2 g moles x / moles x / moles x /
12.2g x 1mole g = .452 moles
15.8 g g x 1mole g =.660

9. The Numerator of the fraction is the coefficient of that column
Al Li(OH)  3Li Al(OH)3
12.2 g moles x 3/ moles x 3/ moles x 3/
12.2g x 1mole g = .452 moles
15.8 g g x 1mole g =.660

10. The denominator of the fraction is the coefficient of the given column
Al Li(OH)  3Li Al(OH)3
12.2 g moles x 3/ moles x 3/ moles x 1/1
12.2g x 1mole g = .452 moles
15.8 g g x 1mole g =.660

11. Do math and label as moles
Al Li(OH)  3Li Al(OH)3
12.2 g moles x 3/ moles x 3/ moles x 1/1
12.2g x 1mole = moles = 1.36 moles = .452 moles g = .452 moles
15.8 g g x 1mole g =.660

12. Covert all moles to grams
Al Li(OH)  3Li Al(OH)3
12.2 g moles x 3/ moles x 3/ moles x 1/1
12.2g x 1mole = moles = 1.36 moles = .452 moles g
1.36moles x g moles x g moles x g mole mole mole = .452 moles = 32.6 g = g = g x x
3.0237
15.8 g g x 1mole g =.660 moles

13. Verify the law of conservation of mass
Al Li(OH)  3Li Al(OH)3
12.2 g moles x 3/ moles x 3/ moles x 1/1
12.2g x 1mole = moles = 1.36 moles = .452 moles g
1.36moles x g moles x g moles x g mole mole mole = .452 moles = 32.6 g = g = g x x
15.8 g g g x 1mole g g =.660 moles

14. ANSWER - Li(OH) Which Chemical is the Limiting Reagent?
(Given chemical in the smaller set of stoichiometry) Al
Which Chemical is the Excess Reagent? (Given Chemical in the larger set of stoichiometry)
- Li(OH)
What is the Amount of Excess??
g g