Limiting Reactant and Percentage Yield in a Chemical Reaction
Introduction: Reactants in any reaction must react in proportions that are dictated by their coefficients in the balanced
reaction. This relationship is based on a mole ratio and not on mass. Reactants that are in lesser amounts will be the limiting
reactant and will determine how much product should be theoretically produced. For reactions carried out in the lab, the
actual yield of the product is often less than the theoretical yield. The difference between the actual yield and the theoretical
yield is calculated as a percentage yield. In this lab you will be studying the reaction of aluminum foil with aqueous copper
(II) chloride to determine the limiting reactant and percentage yield based on the stoichiometric relationship.
Lab Report Details
Title Block and Purpose
Complete a title block at the top of your page and record the purpose of the lab.
Quantitative Observations
Draw and properly title Table 1 for your quantitative observations. Table 1 should contain mass of beaker 1, mass of
beaker 1 and CuCl2 , mass of CuCl2 , mass of aluminum, mass of beaker 1 and Cu, mass of Cu. Include Trial 1, 2, 3, and an
average row. You will complete Trial 1. Trials 1 and 2 will be done by other groups.
Qualitative Observations
Draw and properly title Table 2 for your qualitative observations. Table 2 should contain a physical description (colour,
clarity state) of the reactants (before the reaction) and a description of the products (after the reaction).
Calculations and Analysis
Answer the analysis questions and hand in the rubric with your lab report.
Materials
Apron and goggles
Tall narrow 200mL beaker 1
Stirring rod
Ruler
Bunsen burner
Ring clamp
Retort stand
Wire gauze
Crucible tongs
Forceps (tweezers)
50 mL graduated cylinder
Watch glass
Copper (II) chloride
Heavy dutyAluminum foil
(6 cm X 10 cm strip)
Clean beaker for waste
Procedure
1. Carefully read over the procedure and create your data table using the proper format.
2. Put on your apron and safety goggles. DO NOT take them off until the lab is done.
3. Obtain your materials. Clean and dry all equipment.
4. Add 2 g (or slightly less) of copper (II) chloride to beaker 1. Record the exact mass including all available significant digits
in Table 1.
5. Add 50.0 mL of water to beaker 1. Stir to dissolve.
6. Fold the aluminum foil lengthwise once and again to make a 1.5 cm X 10 cm strip.
7. Coil the foil into a circle and lay on the bottom of the beaker with the copper chloride solution so that the aluminum is
submerged.
8. Clamp the iron ring on the stand and place the beaker on the wire gauze (on the iron ring).
9. Heat GENTLY with the burner for 5 minutes. Ensure a slow boil. Reduce heat if foaming develops.
10. Turn off the burner and allow the solution to cool until you can hold it in your hands.
11. Using the forceps, carefully shake the foil to dislodge the copper from it. Make sure all copper lands in beaker 1.
12. Put the remaining aluminum foil in a clean waste beaker and pick out any copper pieces and return them to beaker 1.
13. Add 50 mL of water to beaker 1 and stir well to wash the copper. Discard most of the water into your waste beaker without
losing any copper pieces. If you lose some copper, pick it out of your waste beaker and return it to beaker 1.
14. Repeat another wash.
15. Spread the copper pieces on the bottom of beaker 1 with the stir rod.
16. Cover the beaker with a watch glass (convex side down) and heat GENTLY to evaporate any water.
17. When it appears dry, remove the watch glass with the crucible tongs and heat gently for 3 more minutes. Make sure the
copper does not turn black, reduce heat!
18. Place a dry cooled watch glass back on top. If condensation appears on the bottom of the watch glass, continue to heat to
remove the water.
19. Repeat steps 18 and 19 until no more condensation appears. Turn off the burner and let cool. Never put a hot beaker on the
balance.
20. Determine the mass of the beaker and copper.
21. Clean up your work area and return all the cleaned materials back to their place. Wipe down your lab bench with soapy
water.
22. Obtain data from two other groups for Trial 2 and 3.
Analysis
1. a) What type of reaction occurred?
b) Write the balanced chemical equation including states.
2. a) Which reactant was in excess? What observation(s) indicated this?
b) Which is the limiting reactant? What observation(s) indicated this?
3. Calculate the following showing all steps and units.
a) Limiting Reactant. Use the average mass of Al from the 3 trials and the average mass of copper(II) chloride from the 3
trials.
b) Theoretical Yield. Use the limiting reactant to calculate the theoretical mass of copper produced.
c) Experimental Yield. Calculate the average mass of copper produced in this reaction.
d) Percent yield. Use the theoretical and experimental yield for this experiment to find percent yield.
5. Discuss accuracy, precision and any error in this experiment in a SHORT paragraph. BE CONCICE!!
SCH-3U
Stochiometry and Percentage Yield in a Chemical Reaction
Communication
Title Block
-Clear, neat, well organized.
-Contains an appropriate title, dates, name and partner’s name.
Purpose
Appropriate general purpose is given in one or two sentences.
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Results - Data Tables
- Appropriate titles at the top
- Well organized and neat (numbers are aligned)
- Units are in the headings
- Contains all relevant data and observations
Overall clarity, neatness, spelling and grammar
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Overall Communication
Inquiry
Experimental Technique reflected by the significant digits
shown and the accuracy of the results
Analysis Question 1
Balanced chemical reaction is complete
Type of reaction identified
Analysis Question 2
Excess and limiting reactants correctly identified and explained
using qualitative and quantitative observations
Analysis Question 3
Limiting reactant, (4)
theoretical yield, (4)
experimental yield and (2)
percent yield (2)
are calculated correctly showing all steps and units
Analysis Question 5
Accuracy and precision, sources of error and ways to improve the
experiment are discussed in a short paragraph
Overall Inquiry
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