LAB: Percentage Yield of Copper
Objective
Using a chemical reaction between iron and copper(II) chloride, determine the number of amount of copper produced and the percentage yield of the copper.
Brief Overview
The chemical reaction to be used is this:
Fe(s) + CuCl2(aq) ---> FeCl2(aq) + Cu(s)
This reaction has a 1:1 mole ratio between iron used and copper produced. The iron will be provided by two iron nails. The copper will initially be in the form of Cu2+ ions in solution.
Safety
1) Wear goggles and an apron during the entire lab, including setting up and cleaning up.
2) Solutions can be spilled when being transferred. Pour solutions with proper care.
Materials List
250 mL beaker, stirring rod, heat lamps or drying oven, sandpaper, electronic balance, copper (II) chloride, two iron nails, distilled water
Procedure
1) Obtain two iron nails, use the electronic balance to weigh both nails. Do them together, not separately. Record this value (to the 0.001 place) in your data table.
2) Using a pencil, write group member's names (initials are OK) and the class period on the empty 250-mL beaker.
3) Zero the balance. Then weigh the beaker. Record this value (to the 0.01 place) in your data table.
Part One: Reacting the iron and copper(II) chloride
5) Put one, rounded spoonful of copper(II) chloride into the 250-mL beaker and record its mass.
6) Using the distilled water bottle, put about 50 mL of distilled water into the 250-mL beaker. Note: this amount is approximate. Use the beaker markings (read from the bottom up) to guide you. Gently swirl the beaker to hasten the CuCl2 dissolving.
7) Place the two nails into the solution. As you do this, watch the nail surface closely. Observe the reaction for 2-3 minutes
8) With more distilled water, fill the beaker to the 150 mL mark, reading from the bottom up. As the water is added use the nails to stir the solution to dissolve any remaining CuCl2. Observe the nails for 2-3 minutes.
9) Allow the nails to sit in the copper(II) chloride solution undisturbed over night.
Part Two: cleaning the copper produced
10) Handle the two nails by the exposed portion, however do not remove them yet from the solution. Shake off the copper adhering to the nails. The copper will settle to the bottom. Rub the two nails together to scrape off as much copper as possible.
11) Pull the nails out of the solution and rinse them off with distilled water, keeping the rinse water in the beaker. DO NOT rinse off the nails into the sink.
12) Set the nails aside on a paper towel and allow to air dry, then weigh them on the electronic balance. Record the value in your data table.
13) Decant means to pour off a liquid while the solid remains in the container. Decant the liquid in the beaker while keeping the solid copper in the beaker. Here is how:
a) start the faucet water gently running in the sink; it does not to be running hard.
b) hold a stirring rod in one hand and the beaker in the other. Bring the stirring rod to the beaker's pouring lip. One person should do the decanting, not two.
c) slowly pour the liquid off while trying to keep the solid undisturbed.
d) do not pour off the last 5 mL of solution. In this manner, you will minimize the loss of solid during decanting. Please realize you will lose some solid, the point is to minimize it.
14) Add about 20 mL of distilled water to the copper, swirl and let the copper settle. Decant into the sink. Add another 20 mL of distilled water, swirl and decant. When done with decanting, let the faucet water run for about 2 minutes and then shut it off.
15) Place your beaker under the heat lamps or in the drying oven, as directed by the teacher.
Part Three: weighing the copper produced
16) When dry, remove from drying oven, allow to cool off and weigh. Record the value in your data table.
Data
Mass of two iron nails (before) / gMass of 250-mL beaker (empty) / g
Mass of beaker + CuCl2 / g
Mass of CuCl2 / g
Mass of two iron nails (after) / g
Mass of 250-mL beaker + dry copper / g
Observations: record observations in a table
Calculations:
1) Calculate moles of iron lost by nails.
2) Calculate moles of copper produced.
3) Calculate the molar ratio of iron lost to copper produced.
4) Find the limiting reactant.
5) Calculate the theoretical yield of copper.
6) Calculate the amount of excess reactant.
7) Calculate the % yield of copper.
Discussion:
1) What is the theoretical mole ratio of iron to copper from the equation? What is the actual mole ration of iron to copper from your data? How do these ratios compare? Explain.
2) What is the excess reactant? If you added more of the excess reactant to the beaker, would you expect more copper to be produced? Explain.
3) Describe 4 possible errors with possible improvements to your lab procedure, telling what the affect on the results would be.
Conclusion:
Describe the relationship between the limiting reactant and the excess reactant. Explain the role of each in producing the products.