Molarity and Dilution Lab - Science with Mrs. Welch



Molarity and Dilution Lab

Chemistry

Part One: Molarity

My group has been assigned to make ____________ mL of a __________ M solution of CuSO4·5 H2O.

1. Calculate the moles of solute needed for your solution. (#1 below)

2. Calculate the number of grams of solute needed to make your solution. (#2 below)

3. Using the electronic balance and weighing tray, weigh out the amount you calculated in #2.

4. Put the CuSO4·5 H2O in your clean 250 mL beaker. Do NOT put into the funnel! The dry powder gets caught, so it needs to be dissolved slightly so that it will go through the funnel into the volumetric flask. Rinse any crystals off the weighing tray using the dH2O squirt bottle or plastic dropper pipet.

5. Add about 50 mL of dH2O and stir with the glass stirring rod.

6. Transfer the solution to the volumetric flask using the funnel. Rinse any leftover solid or solution from the beaker into the volumetric flask with dH2O.

7. Using the dH2O squirt bottle (or dropper), carefully fill to the line with dH2O. DO NOT OVERFILL. IF YOU DO, YOU HAVE TO START OVER.

8. Put the cap (or stopper) onto the flask and invert the flask several times to mix.

Part Two: Dilution

You must make 50mL of a M CuSO4·5 H2O solution using the stock solution your group made in Part 1.

1. Pour your stock solution out of the volumetric flask into the clean, empty 250 mL beaker so that you can pour it easily into a graduated cylinder.

2. Using the dilution formula, calculate the number of mL of your stock solution you need. (#3 below)

3. Using the appropriate graduated cylinder, measure out the amount of stock solution you calculated in #2.

4. Fill the graduated cylinder up to the 50mL line with the dH2O squirt bottle, being careful not to overfill. Put the cap on and invert the flask several times. Compare the color to your stock solution.

5. When your dilution is complete, you will need to share the volumetric flask with your table partners. Pour your diluted solution into a rinsed test tube, labeled with your name and molarity (card & tape provided by Mrs. Welch). Place your beaker along the window sill at the appropriate location. All beakers must be arranged in order of increasing concentration.

Calculations

1. Calculate the moles of solute needed for your solution in part 1.

2. Calculate the number of grams of solute needed to make your solution in part 1.

3. Using the dilution formula, calculate the number of mL of your stock solution you need to make the dilution solution in part 2.

Questions – show calculations and use significant digits where appropriate.

1. Write the formulas for molarity and dilution.

2. Draw a beaker, a graduated cylinder, and a volumetric flask. Compare the uses of each.

3. Explain the pattern you saw in all of the stock solutions arranged on the demonstration table.

4. Calculate the number of moles required to make 100 mL of a 3.0 M solution of CuSO4·5 H2O.

5. Calculate the number of grams required to make 100 mL of a 4.5 M solution of CuSO4·5 H2O.

6. How many mL of a 2.0 M stock solution would be needed to make 100 mL of a 0.75 M solution?

7. Write a sentence explaining how you would make the solution in #6.

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