Name:
In class, you’ve learned to compute how much of a chemical product you can make when you
mix measured amounts of chemical reactants. In this lab, you will be actually using this
information to predict how much product will be made; you will then calculate the percent
yield gained from the amount that you actually recover.
In this investigation, you will use gravimetric stoichiometry to investigate the reaction of
strontium nitrate with excess copper(II) sulfate in an aqueous solution. Use 2.00 g of strontium
nitrate and about 3.5 g of copper(II) sulfate, initially dissolving each chemical in
about 75 mL of water. Be sure to include safety and disposal instructions in your Procedure.
Refer to Appendix C.4 and the Nelson Web site for guidance on various lab techniques.
Strontium nitrate is moderately toxic; there is risk of fire when it is in contact
with organic chemicals, and it may explode when bumped or heated.
Copper(II) sulfate is a strong irritant and is toxic if ingested.
Prelab:
1)
If we mix 25 grams of sodium bromide with a large amount of potassium chloride, what
will our theoretical yield of sodium chloride be?
2)
If our actual yield from this reaction was 18 grams of sodium chloride, what would our
percent yield for this reaction be?
Name:
3)
Is the answer in question 2 reasonable? If so, explain why you think this was a
reasonable answer. If not, explain what is wrong with it and discuss possible reasons
you might get this answer in the laboratory.
4)
What are some factors that might cause our percent yield to be greater than 100%?
What are some factors that might cause it to be less than 100%? Make sure you discuss
specific cases of how both might happen.
Purpose
The purpose of this investigation is to test the stoichiometric method.
Problem
What mass of precipitate is produced by the complete reaction of 2.00 g of strontium nitrate in
solution with an excess of aqueous copper(II) sulfate?
Prediction
Balanced Chemical Equation:
- Reactancts:
o CuSO4 (aq)
o Sr(NO3)2 (aq)
Theoretical Yield:
**Hint** Sr(NO3)2 (aq) is the limiting reagent, so this reactant is used in the calculations.
Name:
Materials
- 2 x 250ml beakers
- Electronic scale
- Ring clamp
- stand
- funnel
- filter paper
- stir rod
- laboratory scoop
- wash bottle
- CuSO4•5H2O (s)
- Sr(NO3)2 (s)
Procedure
1. Obtain materials
2. Prepare Sr(NO3)2 (aq) solution
a. Set 250mL beaker on scale, zero and then measure in 2.00g of Sr(NO3)2 (s).
Record exact amount measured
b. Add about 75ml of distilled H2O and stir to dissolve. Not required to be exact, but
close.
3. Prepare CuSO4 (aq) solution
a. Use the same procedure as step 2.
4. ENSURE BOTH SOLUTIONS ARE FULLY DISSOLVED.
5. Pour the CuSO4 (aq) solution into Sr(NO3)2 (aq), be sure to rinse the CuSO4•5H2O (aq)
beaker with water and pour any rinse into the mixed solution as well.
a. Allow reaction to proceed
6. Take the mass of the filter paper and record in
evidence
7. Set up filtration apparatus
8. Pour solution through filter paper. Do NOT allow the
solution to spill over the top of the filter paper!
9. Thoroughly rinse the beaker & stir rod with water to
ensure no precipitate is left behind.
10. Dry filter paper on a watch glass over the weekend.
Make sure to label your watch glass by laying paper
under it with the names of students in your group.
11. Clean up your station. Dispose of filtrate properly.
Next lab period:
12. Measure the mass of precipitate and filter paper,
record in evidence.
Name:
Evidence
mass of Sr(NO3)2 (s):
mass of CuSO4 (s):
mass of filter paper:
mass of filter paper and precipitate:
Analysis
mass of precipitate:
Evaluation
1. Percent difference and percent yield calculations
2. Evaluate your experiment
- Write a short paragraph about your experimental results.
- Is your prediction verified ? (Within ± 5 %)
Name:
3. Was your percent yield 100%? What factors do you think caused any error that you found?
Explain, using specific examples:
4. Do you think it is common for chemists to get 100% yields for chemical reactions? Why or
why not?
5. If you had to do this lab again, what would you do differently to improve your experimental
results? Explain, using specific examples: