Percent Yield Lab Guidelines

Percent Yield Lab Guidelines
You will prepare a single replacement reaction, write the balanced chemical equation,
calculate the expected value of copper product, and calculate percent yield for your reaction.
Tabulate your copper product data on the back board to share with your class. Calculate the
precision for the entire class’s data. Record the entire lab into your notebook. All sections
apply to this lab, as usual.
To perform the reaction, make a copper (II) sulfate solution (exactly 8.0 g of copper (II)
sulfate pentahydrate in 50 mL of water). Heat the solution to just below boiling and stir to
completely dissolve. After Remove from heat, then gradually stir in precisely 1.55 g of iron
filings, a little bit at a time, stirring gently but continuously. WATCH THE REACTION. Look
closely at what is happening! Let the reaction sit and proceed for 10 minutes, recording
observations. Look for signs that the reaction is complete. Do not forget to record the mass of
filter paper before using it. To isolate the copper product, decant iron sulfate solution, then
rinse with water and decant several more times to rinse the iron sulfate solution off the
copper product. Gravity filter all wet copper product, rinse with more water, use wash bottle to
get all of copper product out of beaker. Allow it to dry until next class. Remove filter paper
from funnel, spread out product and check that it is dry. Measure mass of product on filter
paper. Make a data table for all this data, make it organized, and give it a descriptive title.
CALCULATIONS: *When calculating moles of copper sulfate in your calculations section, get
the molar mass from the bottle of copper sulfate instead of the periodic table! CuSO4 + Fe 
Do limiting reactant/stoichiometry calculations to find the theoretical yield of the copper
product. Then calculate your percent yield.
DISCUSSION: When writing your discussion of theory, tell which reactant is the limiting
reactant, which reactant is in excess, and explain how you know, referring to observations
from the lab.
Describe the technique of decanting. What physical property are you exploiting by using
decanting as a separation technique? Why do you think decanting is a suitable separation
technique for this lab? Tell what the role of the water in the reaction is (why must water be
used to make this reaction happen?). Talk about the dissolving process, talk about the ions.
Discuss the battle over electrons that occurs between the metals (copper and iron). Think
about particles! Connect your discussion of theory to your specific observations in the
ERROR: Look at your PERCENT YIELD. Suggest at least two likely sources of error that lead
to YOUR error (too big or too small). Tell how the error effects data, how significant the error
is, and how it could be avoided if the procedure were to be modified. Calculate the average
deviation for your class’s data. Comment on the precision of your class’s data.
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