Calculate the theoretical yield and % yield of copper.

Question

EX: Aluminum was reacted with copper(II) chloride according to the following reaction: 

2 Al(s) + 3 CuCl2(aq) → 2 AlCl3(aq) + 3 Cu(s)

Mass of aluminum (g)	3.35
Mass of copper(II) chloride (g)	12.50
Theoretical Yield-mass copper (g)	FILL IN
Mass of filter paper (g)	1.25
Mass of filter paper + copper (g)	5.30
Actual Yield-Mass copper (g)	FILL IN

1. Calculate the Theoretical yield of Copper.

2. Calculate the % Yield of Copper in this process.

3. How will the % copper be affected if the filter paper was still wet when the mass of filter paper and copper was made? (% higher, % lower, % unchanged).____________________ thoroughly explain your selection. You may include calculations to assist in your explanation.

Answer 1

First calculate moles of each reactant:

3.35g Al = 0.124 mol

12.5g CuCl2 = 0.0929 mol

When you have amounts for both reactants you need to determine which one is limiting:

Divide each by its coefficient in the balanced equation and compare

0.124 mol Al / 2 = 0.62

0.0929 mol CuCl2 / 3 = 0.310 (smaller value, so this is the limiting reactant

Use the limiting reactants amount to calculate the theoretical yield of Cu:

In the balanced equation the coefficient of CuCl2 and Cu are the same, so the moles of Cu produced is the same as the moles of CuCl2 that is reacted.

0.0929 mol CuCl2 = 0.0929 mol Cu

0.0929 mol Cu = 5.90g Cu (this is the theoretical yield)

The actual yield is obtained by subtracting the filter mass from the Mass of filter paper + copper

5.30 - 1.25 = 4.05g

To answer questions about lab errors, determine which measurement will be affected by the error and then follow that through the calculation. If the filter paper was still wet then the "Mass of filter paper + copper" would be too high. This measurement was used to find the actual yield. If it is too high, then the actual yield would be too high. If the actual yield is too high then the percent yield would be too high.