Solution Preparation Lab
Georgia Performance Standards:
SC7 a: Explain the process of dissolving in terms of solute/solvent interactions:
· Observe factors that affect the rate at which a solute dissolves in a specific solvent.
· Express concentrations as molarity.
· Prepare and properly label solutions of specified molar concentration.
SCSh3. Students will identify and investigate problems scientifically.
· Develop procedures for solving scientific problems.
· Collect, organize and record appropriate data.
· Develop reasonable conclusions based on data collected.
· Evaluate whether conclusions are reasonable by reviewing the process and checking against other available information.
Introduction
Preparation of a solution is an essential skill in the study of chemistry. The solutions which are prepared are often used in determining quantitative relationships in chemical reactions. In this activity you will prepare a standard solution of a substance called copper(II) sulfate pentahydrate. You will then dilute this solution to the desired concentration. The overall essential questions that you want to keep in mind are the following: How are solutions measured? & How do you prepare a solution at a specific concentration?
Purpose
Part A: To prepare a solution of copper(II) sulfate pentahydrate of known concentration.
Part B: To dilute the solution prepared in Part A to a specific concentration.
PreLab Assignment
Calculate the number of moles and mass of CuSO4•5H2O required to prepare 100.0 mL of 0.100 mol/L solution. (Be sure to include all details of this calculation in your report.) View teacher demo for information on pipetting techniques and solution preparation that will assist you in this activity.
Materials
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Per group of students
· 1 centigram balance
· 2- 250 mL beaker
· 1 bottle containing copper(II) sulfate pentahydrate (CuSO4×5H2O)
· 1 scoopula
· 1-10 mL delivery pipette
· 1 disposable pipette
· 1 pipette bulb
· 2-100 mL volumetric flasks (with stoppers)
· conductivity apparatus
· deionized water in a wash bottle
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Safety
Copper(II) sulfate pentahydrate is a toxic substance. Be careful when working with the required quantities and when preparing the solution. If you should spill any copper(II) sulfate pentahydrate on your hands, wash them well. Wear safety glasses and a lab coat/apron during this activity.
Procedure
Read this procedure completely before you enter the lab. As you read, you will notice that there are two kinds of observations to be made in this activity: quantitative observations such as recording measured values and qualitative observations such as colour intensity and conductivity. As you read the procedure, sketch a table that you can use to record your observations.
Part A
1. Zero/Tare the balance. Determine the mass of a clean, dry 100 mL volumertric flask. Record the mass on the data table.
2. Take the mass of an empty weigh boat and record it on the data table.
3. Leave the empty weigh boat on the balance and zero/tare the balance again. Add solid CuSO4 crystals to the volumetric flask using a scoopula until the balance levels the mass calculated in the pre-lab assignment.
4. Bend the weigh boat and transfer the CuSO4 crystals to the volumetric flask. With distilled water, rinse the remaining CuSO4 crystals in the weigh boat into the volumetric flask.
5. Record the mass of the volumetric flask + the CuSO4 added on the data table.
5. Subtract the empty volumetric flask from the (volumetric flask + CuSO4) to determine the exact amount (in grams) of CuSO4 added. Record all mass measurements in your data table.
6. Using the wash bottle, add approximately 50 mL of deionized water to the volumetric flask to dissolve the CuSO4 crystals. Cap and invert the volumetric flask until the CuSO4 has all dissolved.
7. Using the wash bottle, carefully add deionized water to the volumetric flask until the meniscus reaches just below the 100.0 mL mark. Cap and invert the volumetric flask until the remaining CuSO4 has all dissolved.
8. Use a disposable pipette to carefully bring the bottom of the solution meniscus to the 100.0 mL mark on the volumetric flask. Cap and invert the volumetric flask until the remaining CuSO4 has all dissolved. Record volume added in data table.
9. Make observations on the color intensity of the solution and record them in your table. Label your volumetric flask.
10. Do not discard the solution. You will need to use it again in Part B and Part C.
9. Calculate the exact concentration of your solution in Part A and record it on the data table. Show work in box. (Grams of CuSO4 in flask à comvert to moles à divide by the total vol. in flask)
Part B
Now you will dilute the solution in part A to one-tenth of its concentration in part B.
1. Using the 10.0 mL delivery pipette, transfer exactly 10.0 mL of Part A solution to another 100.0 mL volumetric flask. Record volume transferred on data table.
2. Using the wash bottle, carefully add deionized water to the volumetric flask until the meniscus reaches the 100.0 mL mark. Cap and invert the volumetric flask until the remaining CuSO4 has all dissolved. Record volume added on data table.
3. Record observations on the color intensity of the diluted solution in your table. Label your volumetric flask.
4. Calculate the concentration of your solution in Part B and record it on the data table. Show work in box. Hint: M1V1 = M2V2
Part C
1. Pour all of each CuSO4 solution into its own 50 mL beaker. Label the beakers A & B.
2. Use a conductivity tester to test the electrical conductivity of each solution. Rinse probe with water after each new solution tested.
3. Record the values in units of “mS” in your table.
Results
Present your quantitative and qualitative observations in a neat and well organized table.
PART A:Mass of Clean, dry 100 mL Volumetric Flask
Mass of 100 mL Volumetric Flask + CuSO4
Exact mass of CuSO4 added
Total Vol. of H2O added to volumetric flask in Part A
Color/Intensity of Solution in Part A
Calculated “EXACT” solution concentration in Part A
PART B:
Volume of 0.100 M solution transferred from Part A to Part B
Total Volume in flask for part B
Color/Intensity of Solution in Part B
Calculated “EXACT” solution concentration (Molarity) in Part B. Hint: Use this equation (M1V1=M2V2)
PART C:
Electrical conductivity of Solution from Part A
Electrical conductivity of Solution from Part B
Analysis
1. Use the Molarity formula to calculate the molar concentration of your solution in part A. Show all work. M = moles of solute/liters of solution
2. Use the dilution formula to calculate the molar concentration of the diluted solution in Part B. M1V1=M2V2. Show all work.
3. Compare the color intensity of the original and diluted solutions, and account for the differences in terms of the number of moles of solute in each 100.0 mL volume.
4. Compare the electrical conductivity of the original and diluted solutions. In terms of the relative amounts of dissolved ions in each solution, account for the different conductivities of the solutions.
Conclusion
Make a general statement about the differences between concentrated and dilute solutions.
Extension
1. Let's say you measure out 20.0 mL of the original CuSO4 solution and 40.0 mL of the diluted CuSO4 solution. Which solution contains more moles of solute? Support your choice with detailed calculations.
2. Draw labeled diagrams to illustrate the differences between a graduated pipette and a delivery pipette.
3. Describe a situation in which you would you use a graduated pipette instead of a delivery pipette.
4. Is blowing the last drop out of a delivery or graduated pipette considered to be proper technique? Explain why. Don’t just say yes or no.
5. Why should you never draw a solution into a pipette by mouth?
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