Formal Lab
Limiting Reactant and Percentage Yield in a Chemical Reaction
Introduction
Reactants in any chemical reaction must react in proportions that are dictated by their coefficients in the balanced
reaction. This relationship is based on a mole ratio. The reactant that is completely used up is called the limiting reactant,
and the reactant that is left over is called the excess reactant. The limiting reactant is used to calculate how much product
should be theoretically produced (theoretical yield). For reactions carried out in the lab, the actual yield of the product is
often less than the theoretical yield. The percentage yield is used to compare how efficient a reaction is by comparing the
amount of product produced in the experiment to the amount of product that should be produced according to the
stoichiometry calculation. 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.
Aluminum + Copper(II)chloride 
*****************************************Prelab***************************************************
This lab takes the whole class period so you must have your Title block, Purpose, Table 1 and Table 2 prepared before class
on the day of the lab.
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Lab Report Details
Title Block
Complete a title block at the top of your page. Include a descriptive title, your name, your partner’s name, the date the lab
was performed and the date the lab is due.
Purpose
In two or three sentences record the purpose of the lab. Be specific.
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.
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
DRY 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 duty aluminum foil
Clean beaker for waste
Procedure
Set Up
Carefully read over the procedure and create your data table using the proper format.
Put on your apron and safety goggles. DO NOT take them off until the lab is done.
Obtain your materials. Clean and DRY all equipment.
Reacting Aluminum and Copper (II) Chloride
4. Add about 1.5 g of copper (II) chloride to beaker 1. Record the exact mass including all available significant digits in Table 1.
5. Add about 50 mL of water to beaker 1. Stir to dissolve.
6. Record your physical description of the Al and copper(II)chloride solution in Table 2 under reactants. (colour, clarity, state)
7. Cut out a piece of aluminum foil 8 cm x 12 cm and fold it twice lengthwise. Record the mass of Al in Table 1(it should be
about 0.5g).
8. 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.
9. Clamp the iron ring on the stand and place the beaker on the wire gauze (on the iron ring). Heat GENTLY with the burner
(slow boil) for about 5 minutes or until the solution changes colour. Reduce heat if foaming develops.
10.
Turn off the burner and allow the solution to cool until you can hold it in your hands.
1.
2.
3.
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Formal Lab
Isolating the Copper
11. To get copper all alone in beaker 1, remove the aluminum and remaining solution from beaker 1. To do this, use tweezers to
carefully shake the aluminum foil and dislodge the copper from it, then pour the liquid into the clean waste beaker.
If pieces of copper fall into the waste beaker, move them back to beaker 1 using the tweezers.
12. Add about 50 mL of water to beaker 1 to wash the copper and stir. Pour the water into the 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.
13. Repeat another wash.
14. Spread the copper pieces on the bottom of beaker 1 with the stir rod.
15. Heat GENTLY to evaporate all water. Hold the watch glass over the beaker periodically to check for condensation. If you
see condensation, there is still water in the copper. When no condensation appears, heat for 1 more minute. Make sure the
copper does not turn black!
16. Turn off the Bunsen burner and let the beaker cool before recording the mass of copper. Never put a hot beaker on the
balance- it will destroy the balance!
Clean Up
17. Dispose of all metals and solutions in the metal waste bucket. Clean up your work and glassware. Return all the cleaned
materials back to their place. Wipe down your lab bench with water.
18. Obtain data from the other groups in your class.
Calculations
1.
2.
Write the balanced chemical equation including the states. (4 marks)
Calculate the following showing all steps and units.
a) Limiting Reactant. Calculate the limiting reactant for your experiment. (5 marks)
b) Theoretical Yield. Use the limiting reactant to calculate the theoretical mass of copper produced in your experiment.
(3 marks)
c) Percent yield. Use the theoretical yield and experimental yield to calculate percent yield for your experiment. (3 marks)
Discussion
Sum up your results in paragraph form
* Name the type of reaction that occurred. Say what your reactants are and what each looked like before the reaction. Say what
your products were and what each of them looked like after the reaction. Note any changes in the colour of the solution. (6 marks)
*Say which reactant was the limiting reactant according to your calculations. Explain how your physical observations support (or
do not support) this calculation. (3 marks)
*Say what the percent yield was for your experiment.
Was your experiment accurate? (compare to theoretical) Explain.
Was your experiment precise? (compare to class data) Explain.
Discuss why the percent yield is not exactly equal to your theoretical yield. (6 marks)
*Discuss the strengths and limitations of the methods you used. Explain any failed methods and suggest reasons for why they
failed. Say how the experiment could be improved. (4 marks)
*Discuss the importance of knowing the percent yield in the field of chemistry. (2 marks)
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.
Observation Data Tables
- Appropriate titles at the top (2)
- Well organized and neat (numbers are aligned) (1)
- Units are in the headings (1)
- Contains all relevant data, sig figs and observations (Table 1:3 marks)(Table 2:8 marks)
General Communication
-Overall clarity, neatness, spelling and grammar
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Inquiry
Experimental Technique
-Reflected by the significant digits shown and the accuracy of the results
Calculations
-See mark distribution in calculation instructions
Discussion Questions
-See mark distribution in discussion instructions
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Formal Lab
Table 1:
Mass
Beaker 1
Beaker 1 +
Copper(II)chloride
Copper(II)chloride
Aluminum
Beaker 1 + Copper
Copper
Table 2:
Chemical
Physical Description
Reactants
Products
Revised Oct 2013
Formal Lab
Revised Oct 2013