Analía Bellizzi – Chemistry Classes

Ronald Reagan High School

AS Solution Preparation and Dilution

Solution Preparation and Dilution

Solution Preparation-dilution

 

SECTIONS TO SHOW IN THE REPORT (FOR PARTS A B AND C SEPARATELY)

  • PURPOSE
  • MATERIALS
  • PROCEDURES
  • SETUP (graph)
  • DATA TABLES AND CALCULATIONS

AT THE END OF THE THREE PARTS:

  • DISPLAY THE FOLLOWING TABLE (show calculations on how you obtained every value for the table)
SOLUTION      CONCENTRATION

(mol/L)

# of moles of solute in 100 cm3 grams of solute in 100 cm3  COLOR                 CONDUCTIVITY

(Volts) 

 1) concentrated
 2) diluted
 3) 1/2 – 1/2
  • ANSWER THE ANALYSIS QUESTIONS
  • ANSWER THE EXTENSION QUESTIONS

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(lI) sulfate pentahydrate. You will then dilute this solution to the desired concentration.

Purpose of the lab

Part A: To prepare a solution of copper(lI) sulfate pentahydrate of known concentration.

Part B: To dilute the solution prepared in Part A to a specific concentration.

Part C: To test the difference in conductivity for the solutions prepared.

Pre-lab Assignment

  • Calculate      the number of moles and mass of CuSO4·5H2O(s) required to prepare 100.0 mL of 0.100 M solution. (Be sure to include all details      of this calculation in your report.) – (Question 1 in the analysis)
  • Check with your teacher BEFORE you prepare the solution to be sure your calculations are OK.
  • Your teacher will check only calculations that show very clearly the step by step and include units.
  • Information on pipetting techniques will be provided by your teacher so as to the step by step for the preparation of the solution.

Materials

Per group of students

– Triple beam balance

– 250 mL beaker

– Copper (lI) sulfate pentahydrate CuSO4·5H2O(s)

– Stirring rod

– Funnel

– Scoopula or spatula

– 10 mL delivery pipette

– Medicine dropper

– Pipette bulb

– 100 mL volumetric flasks (with stoppers)

-conductivity apparatus

-Deionized/Distilled water in a wash bottle

Safety

  • Copper (lI) sulfate pentahydrate is a toxic substance and it will stain your hands/nails.
  • If you spill any copper (lI) sulfate pentahydrate on your hands, wash them well.
  • Wear safety glasses 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. Determine the mass of a clean, dry 250 mL beaker.
  2. Record the mass.
  3. Preset the balance riders to the mass of the beaker plus the calculated mass of the solute (see your answer from the pre-lab activity).
  4. Add solid CuSO4·5H2O(s) crystals to the beaker using a scoopula until the balance beam levels.
  5. Record all mass measurements in your data table.
  6. Using the wash bottle, add approximately 50 mL of deionizer/distilled water to the beaker to dissolve the CuSO4 crystals.
  7. Stir the solution with a clean stirring rod until the CuSO4·5H2O(s) has all dissolved.
  8. Using a clean funnel, transfer the solution which you have just prepared from the beaker into a clean 100 mL volumetric flask.
  9. Use the wash bottle containing the deionized water to rinse any solution from the stirring rod, the beaker, and then the funnel into the volumetric flask. Be careful, do not use MORE water than needed to fill out the volumetric flask.
  10. Use a plastic pipette to carefully bring the bottom of the solution meniscus to the 100.0 mL mark on the volumetric flask.
  11. Stopper the volumetric flask and invert several times.
  12. Make observations on the colour intensity of the solution and record them in your table.
  13. Do not discard the solution. You will need to use it again in Part B and Part C.

Part B

You have prepared 100.0 mL of a 0.100 mol/L solution of copper (lI) sulfate, in Part A. Now you will dilute this solution to one-tenth of its concentration.

  1. Using the 10.0 mL delivery pipette, transfer exactly 10.0 mL of the 0.100 mol/L CuSO4 solution to another 100.0 mL volumetric flask.
  2. Using the wash bottle, carefully add deionized water to the volumetric flask until the meniscus reaches the 100.0 mL mark.
  3. Stopper the volumetric flask and invert several times.
  4. Record observations on the color intensity of the diluted solution in your table.
  5. Transfer the solution you just prepared into a labelled beaker reading “concentrated”.
  6. Rinse the volumetric flask twice with tap water and twice with distilled water.

Part C

  1. Pour 10 mL of each CuSO4·5H2O(s) solution into one 50 mL beaker. (you will be mixing the two solutions in equal proportions in the same beaker
  2. Use a conductivity tester to test the electrical conductivity of each solution. Record the observations in your table.

Results

Present your quantitative and qualitative observations in a neat and well organized table. Include your calculations USING UNITS.

Analysis – COPY THE FOLLOWING QUESTIONS and answer them based in your results:

  1. How many grams of CuSO4·5H2O(s) were necessar to prepare 100.0 mL of a solution 0.100 M? (Show your work and units)
  2. Did you include the mass of the water in your measurements? Why?
  3. Why do you need to record the mass of the dry beaker?
  4. Why is it important to rinse several times the beaker; the funnel and the stirring rod and include this liquid      in the solution?
  5. Which is the molarity of the solution prepared in PART A?
  6. Read again step 9 of PART A.  The second sentence says “BE CAREFUL……” Why is this important?
  7. Why do you need to stopper the volumetric flask and invert it several times?
  8. What happens if you skip this step?
  9. How many moles of solute did you extract in the 10 mL of the solution A to form the new diluted solution?
  10. Use the dilution formula to calculate the molar concentration of the diluted solution. Show all work.
  11. Compare the colour 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.
  12. 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. Use 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?
  5. Why should you never draw a solution into a pipette by mouth?