Solution Stoichiometry Experiment Group
(Dr Elcesser and Mr. Palko)
Purpose
In this experiment group, you will use the principles and techniques of solution stoichiometry - moles, volume, molarity, pipetting and titations - to analyze a number of different acids and bases. Being able to create, use and analyze solutions of particular concentrations is a fundamental skill for anyone working in a laboratory.
Goals of the Labs
Solution Stoichiometry #1: Acid-Base Titrations with Chemical Indicators
 standardize solutions of HCl and NaOH.
 use a chemical indicator to signal the end-point of the reaction.
 calculate the number of moles of an acid or base present at the equivalence point.
Solution Stoichiometry #2: The Analysis of Eggshells for Calcium Carbonate
 use techniques and concepts from previous experiments to determine the amount of calcium carbonate in an eggshell.
Scenario: Reduce, Recycle, Reuse
Eggshells are made up primarily of calcium carbonate, CaCO
3
. Putting them in a compost heap is a recommended way to add calcium to garden soil. However, most people simply toss eggshells in the trash, because it is too challenging to clean them thoroughly enough to discourage rodents from invading their compost. That landfills are bulging all across the United States is indisputable. Is there a way to put this discarded calcium carbonate to better use?
The CheePaper Company, where you have an internship in the research division, has been making paper in the area for decades. Unfortunately, the aroma of a paper mill reaches tourists long before they arrive. In the current economy, it is the revenue of tourism that will carry the city through the recession. CheePaper has laid off employees but demand for paper continues to increase. Image consultants have recommended that CheePaper look for “greener” practices to “improve the quality of life” in the community. Recycling paper is an environmental and socially attractive solution, but recycled paper requires extra bleaching to make the paper bright enough for consumer use. One of the basic materials for bleaching paper is calcium carbonate. At CheePaper, a research and development scientist has suggested they consider mining the local landfill for calcium carbonate. The Public Relations
Department has jumped all over this suggestion stating that not only could CheePaper recover useful materials but also could use this as an opportunity to color themselves “green” by helping reduce the landfill volume. CheePaper knows that “green” companies give back to the community and gain valuable positive press. Your supervisor’s lab has been charged with determining the viability of recovering calcium carbonate from discarded eggshells . Your job is to determine how much calcium carbonate can be recovered from a typical eggshell. Fortunately, the logistics of an efficient way to isolate eggshells from the rest of the residual waste is the charge of another department. Several options exist for the determination of calcium carbonate content of eggshells.
In Experiment 1, you will learn about solution stoichiometry by exploring chemical reactions between acids and bases (Calcium carbonate is a base.) and you will prepare standardized solutions of
HCl and NaOH to use in Experiment 2 where you will determine the amount of calcium carbonate in eggshells

Solution Stoichiometry #1: Using Titration to Standardize HCl and NaOH solutions.
(P. Palko)
Pre-laboratory Assignment
1.
Write the chemical formula and calculate the molar mass for each substance: a) hydrochloric acid b) sodium hydroxide c) potassium hydrogen phthalate
2.
Write the balanced chemical equation for the reaction between each solution: a) hydrochloric acid and sodium hydroxide b) potassium hydrogen phthalate and sodium hydroxide
3 a) What mass of potassium hydrogen phthalate would react with 15.0 ml of a 1.0 M NaOH
solution. b) If 14.75 ml of NaOH solution was required to titrate a solution containing 3.015 g of potassium hydrogen phthalate, what is the molarity of the NaOH?
4.
If 15.00 ml of 1.05 M HCl is required to reach the endpoint of the titration of 20.0 ml of
NaOH solution, what is the molarity of the NaOH solution?
5.
If you plan to titrate the NaOH that was described in #4 with a solution of HCl that you suspect is about 0.5M what would be an appropriate volume of NaOH to place in a flask into which you plan to add the HCl using a 50 ml buret? Explain your answer.

Solution Stoichiometry #2: The Analysis of Eggshells for Calcium Carbonate
(W.E. Elcesser and P. Palko)
Pre-laboratory Assignment
Read the experiment and answer the questions below before coming to lab. The prelab will help you decide quantities of materials to use in your experiment, for whichever method of analysis you choose.
1.
Write the balanced equation for the reaction between CaCO
3
(s) and HCl(aq).
2.
Direct titration: A particular clean, dry eggshell weighs 5.27 g. You decide to titrate the eggshell directly with HCl, and start with the "worst case scenario," assuming that the eggshell is 100% calcium carbonate.
(a) If the eggshell is 100 % calcium carbonate, how many moles of CaCO
3
would be present?
(b)
Based on your balanced equation, how many moles of HCl would be needed to react with the moles of calcium carbonate in 2(a)?
(c) If [HCl] is 1.000 M, what minimum volume of HCl is needed to react with the CaCO
3
in
2(a)? Is this a volume of HCl that can be dispensed without refilling a 50.00 mL buret?
(d)
Suppose you do want to dispense between 10.00-35.00 mL of 1.000 M HCl from your buret (this takes advantage of the four significant figures that can be obtained from a buret). What mass of eggshell should you aim to analyze, assuming it is 100% CaCO
3
?
(e) If you decide to directly titrate a solid piece of eggshell with HCl from a buret, describe how you will ensure that you have reacted 100% of the calcium carbonate, without overshooting the endpoint.
(f)
What are advantages and disadvantages of direct titration in this case?

3.
Back titration You decide to first react all the calcium carbonate in the eggshell with excess
1.000 M HCl, and then do a back titration with 1.000 M NaOH to determine the amount of leftover HCl.
(a) If you use a 25.00 mL pipette to dispense 1.000 M HCl, how many moles of HCl are present?
(b) Use the balanced reaction in question 1 to find the maximum mass of CaCO
3
that could be reacted with this amount of HCl. This is the maximum mass of eggshell you would want to use in a trial.
(c) After reaction with the eggshell, you want enough leftover HCl that you can titrate it with a reasonable quantity of NaOH. Give that, and your results in 3(b), what would be a reasonable mass of eggshell (assuming 100 % CaCO
3
) to use?
(d) With your mass is 3(c), how many moles of HCl would be consumed by the eggshell?
How many moles of the HCl would be leftover?
(e) Use your balanced reaction equation from Experiment #1, pre-lab question 2a to find the volume of 1.000 M NaOH would be needed to neutralize the leftover HCl as determined in 3(d)?
(f) Does your answer in 3(e) require more than one filling of a 50 mL buret? Does it take advantage of the four significant figures of a buret? Explain.
(g) If you decide to back-titrate the leftover HCl with NaOH in a buret, describe how you will find the endpoint, without overshooting it.
(h) What are advantages and disadvantages of back titration in this case?

4.
Mass stoichiometry: You decide to add an excess of 1.000 M HCl to 0.567 g of an eggshell and then determine the mass of CO
2
produced by this reaction and then use that to determine the mass of CaCO
3
in the eggshell. a) Use the balanced equation from question 1 to determine the volume of 1.000 M HCl required to insure complete reaction of all CaCO
3
in the eggshell. As before, assume the eggshell is
100% CaCO
3
to insure addition of excess HCl. b) If all the CaCO
3 in the eggshell reacts, what mass of CO
2
would be produced? c) Can you actually determine the mass you calculated in part b using a balance that is capable of reading + 0.01? Explain. d) What mass of eggshell would be required to produce results that allow for the calculation of the % CaCO
3
with 4 significant digits? (Note: 1.000 g is the smallest mass that can be obtained with 4 significant digits using the most precise balance in room 215.) Is the mass of eggshell and volume of 1.000 M HCl needed to produce this amount of CO
2
practical? e) What are the advantages and disadvantages of using mass stoichiometry in this case?

Solution Stoichiometry #1: Preparing Standardized Solutions of NaOH and HCl
The preparation of an aqueous solution of known concentration is generally a straight forward process. Generally one works from the desired concentration and volume and calculates a mass of solute to be dissolved. The mass of solute can be then added to a container, usually some sort of volumtric flask, and then the appropriate amount of water can added to dissolve the solute. In the case of the solutions needed for experiment #2, such a preparation is complicated by the fact that NaOH is a hydroscopic substance and that HCl is only available as solution in the first place.
The fact that NaOH is hydroscopic makes an accurate determination of mass impossible as it absorbs water while sitting on the balance. HCl is obtained as a 12 M solution from chemical suppliers and this is typically diluted to prepare solutions with approximate concentrations.
Thankfully, there is a solid acid (KHC
8
H
4
O
4
) that can be utilized to prepare a solution with a precise concentration. This solution can be used to “standardize” a prepared NaOH solution which in turn can be used to standardize an HCl solution. The process used to determine these concentrations is known as a titration.
Procedural Notes: Work with a partner.
1.
Use the results of your calculation in prelaboratory question #3 to determine the amount of potassium hydrogen phthalate to add to about 30 ml of water in a flask. Add a few drops of phenolthalien indicator to this solution. Place the 1 M NaOH solution into a buret and titrate the potassium hydrogen phthalate solution.
2.
Use the 1 M HCl solution and titrate 15.0 ml of the 1 M NaOH solution. Add a few drops of methyl red to the NaOH solution and place the HCl in the buret.
Calculations:
Use your data to calculate the concentrations of the HCl and NaOH solutions.

Solution Stoichiometry #2: The Analysis of Eggshells for Calcium Carbonate
Re-read the scenario on pages 1 and 2.
For this application lab, you will need to choose a procedure to determine the calcium carbonate content in a typical chicken eggshell. You may use any of the techniques that you have learned in the laboratory.
So far in lab, you've learned how to perform gravimetric analysis (mass stoichiometry), and how to do titrations (solution stoichiometry). You've learned to correctly use graduated cylinders, volumetric flasks, volumetric pipettes, burettes, chemical indicators and vacuum filtration - all while wearing safety goggles! You can calculate density, convert grams to moles, convert volume and molarity to moles, convert moles of one compound into moles of another compound and calculate percent mass. Which of these techniques and skills should you apply to determine the calcium carbonate in an eggshell? Since calcium carbonate is a base, it will react with an acid to produce water, a salt, and carbon dioxide. This reaction presents a number of alternatives:
Mass Stoichiometry:
You could react the calcium carbonate in the eggshell with excess HCl to react all the calcium carbonate, leaving behind water, calcium chloride and the rest of the eggshell. Then you will need to somehow isolate the material that didn't come from calcium carbonate and use that mass to decide what percentage of the eggshell is calcium carbonate. Or, you could separate the unreacted solid from the reaction mixture and the evaporation of the solvent from the aqueous products would allow the mass of CaCl
2 to be used to determine the amount of CaCO
3
. Still another alternative is to take advantage of the Law of Conservation of Mass: weigh the eggshell and the hydrochloric acid separately and then weigh the resulting solution recognizing that the weight loss is due to carbon dioxide produced in the reaction of HCl and CaCO
3
.
Solution Stoichiometry:
You could titrate the eggshell directly or use back-titration. If you decide to use titration as part of your analysis, you will need to decide upon an approximate sample size so that the titration uses a titrant volume that gives four significant figures for your volume measurement.
After completing the pre-lab questions, you should discuss with your group the advantages and disadvantages of mass stoichiometry vs. solution stoichiometry to perform the egg shell analysis, and then pick one of these analytical methods to adapt for your procedure. Whatever method you choose, you will need to determine appropriate sample sizes and collect appropriate data. Keep in mind the following guidelines:
1.
You will need to remove the membrane from the eggshell (after discarding the egg white and yolk). Membrane removal is easier to do from a hard-boiled egg. If necessary, you will need to hard-boil the egg first. This takes approximately 20 minutes after the water starts to boil. The recently hard-boiled egg will be hot so you will need to cool it down by running cold water over it.
2.
The eggshell should be as dry as possible so you will need to dry it in the oven for at least 10 minutes. The eggshell can be in fragments or crushed with a mortar and pestle.
3.
Use no more than half of a single eggshell to reduce time in the analysis.
4.
You should repeat any procedure that you choose to reduce random error.
5.
Remember the data you collect must have some relationship with the amount of calcium carbonate that is in the original sample.

Report Tutorial for Solution Stoichiometry #2: The Analysis of Eggshells for Calcium Carbonate
This is a general guide to the information that should be included in your lab report – listen to your instructor for their specific instructions.
Title of Experiment:
Report Submitted by:
Partners:
Date Submitted:
Purpose: Describe in your own words the objective of the experiment, using 2-3 complete sentences.
Procedure:

Make a list of the students in your group and describe the major roles they played in the experiment
 Briefly describe the method that you used to achieve the objective. Justify the method (mass stoichiometry or solution stoichiometry) you picked to analyze the calcium carbonate content of the egg shells.

List the apparatus and the solutions and chemicals (including their concentrations) that you used.
Data and Results:

Include a table that shows all the data that you collected and the values you calculated to determine the percent calcium carbonate content of the eggshell.

Describe how you decided on an appropriate sample size to take full advantage of the precision of the equipment that you used,

Show a set of sample calculations for each calculation you did to determine the percent calcium carbonate in the eggshell.

Calculate the average value for the percent calcium carbonate in the eggshell.
Conclusions: Answer the questions below, as directed by your lab instructor.
1.
Write the balanced chemical equation for the reaction of the calcium carbonate with hydrochloric acid.
2.
Include any other balanced equations that are appropriate to the method that you used to determine the calcium carbonate content of the eggshell.
3.
Calculate the average % calcium carbonate in the eggshells. Discuss the range of values of the percent calcium carbonate. What factors might contribute to any variability in the values?
4.
List other businesses that might be interested in the calcium carbonate content of eggs (Hint: what function does the eggshell serve?)
5.
Assume that 70% of the discarded eggshells in the local landfill can be reasonably recovered. If the landfills in the state where CheePaper is located receives 37 million pounds of discarded eggshells per year, how many grams of calcium carbonate could be recouped? If calcium carbonate costs
$112.50/500g, how much is the recovered calcium carbonate worth?
Instructor notes:

The prelab assignment works well as an in-class activity. It requires about 80 minutes. Have students work in small groups. Groups of 4 work well, particularly if the class has done POGIL style activities. Groups can split up to collect actual data.
It might be useful to demonstrate a titration.
Provide multiple containers of KHP for the first titration. It is helpful to have balanced capable of weighing 0.001 g and this is referenced in pre-lab question #4d. Change this question to reflect the available balances in your lab.
2.5 L of 1 M HCl and 2.5 L of 1 M NaOH should be sufficient for 30 students.
Two different indicators are used in the first experiment to give students experience seeing a variety of color changes as end-points. Either one works for each titration.
Eggs can be pre-boiled to save time.
The two labs and pre-lab activities if done in class will take about 240 minutes of class time.
The inquiry aspects of these experiments have students determine appropriate sample sizes in the first experiment.
The pre-lab essentially tells students appropriate amounts. In the second experiment, students must select an appropriate method and then design the experiment. Again, the pre-lab should guide students in the design aspects of the procedure. Students may select a method and then after beginning, decide they made a bad choice. The direct titration of an eggshell is incredibly slow and finding the end-point is a challenge. It can be done but requires more time and patience than the back titration. Students will typically rush the back titration, not allowing for the complete reaction of CaCO
3
and HCl. The same issues will occur with mass stoichiometry determinations.
Be sure to review safety concerns with students. Goggles and aprons are required. Titrated samples can be disposed of in the drain. Excess NaOH and HCl can be mixed to neutralize and then the resulting solution be dumped in the drain.
Materials needed:
50 ml burets + stands
Flasks and beakers
Magnetic stirrer (optional)
Indicators (phenolthalien and methyl red)
Potassium hydrogen phthalate
1 M HCl and 1 M NaOH
Eggs
Drying Oven
Authors:
Dr. Wendy Elcesser
Indiana University of PA Chemistry Department
Indiana, PA 15701
Philip Palko
Chemistry Teacher
Indiana HS
Indiana, PA 15701 ppalko@iasd.cc