Name:___________________________________ Date:_________________ Period:_____
Name:___________________________________
Name:___________________________________
LAB: The Dilution Solution
(Molarity and Dilution)
Introduction :
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Solutions are an important part of chemistry. In this lab you will practice preparing solutions of different concentrations. The amount of solute that is dissolved in a given quantity of solvent is expressed as the concentration of the solution. A dilute solution contains only a small amount of solute in a given amount of solution. The unit chemists use most often to describe concentration of solutions is molarity. The molarity, M , of a solution is the number of moles of solute per one liter of solution.
Purpose :
- To accurately prepare a solution of known concentration.
M = mol solute
L
- To accurately dilute this solution to a desired concentration.
Materials :
M
1
V
1
CuSO
4
·5H
2
O weighing boat (plastic dish) balance
= M
2
V
2 funnel 100-mL volumetric flask test tube (3) wash bottle deionized (DI) water test tube rack
1-mL plastic pipet 10-mL graduated cylinder
Prelab Questions: (8 points) (2 pt each)
1. What is the molar mass of copper (II) sulfate pentahydrate, CuSO
4
·5H
2
O?
(remember to include the mass of 5H
2
O)
2. How many grams of copper (II) sulfate pentahydrate would be needed to prepare 100. mL of a 0.500 M CuSO
4
·5H
2
O solution? Show your work.
3. Calculate the volume of 0.500 M copper (II) sulfate solution, in mL, that must be diluted to prepare 10.0 mL of a 0.250 M copper (II) sulfate solution. Show your work.
4. Calculate the volume of 0.500 M copper (II) sulfate solution that must be diluted to prepare
10.0 mL of a 0.0500 M copper (II) sulfate solution. Show your work.
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Data Table : ( 15 points )
Volume (in mL) of
Original Concentrated
Solution added (V
1
)
Concentration of
Original Concentrated
Solution (M
1
)
Volume (in mL) of dilute solution (V
2
)
Test Tube #1 Test Tube #2 Test Tube #3
Concentration of dilute solution (M
2
)
Color Rank 1-3 lightest blue = 1 darkest blue = 3
Questions : ( 7 points )
1. Compare the concentrations of each of the serial dilutions to the color rankings. What is the relationship between concentration and color intensity? ( 1 pt.
)
__________________________________________________________________________
__________________________________________________________________________
2. Calculate the number of grams of potassium iodide (KI), needed to prepare 500.0 mL of a
0.125 M KI. SHOW WORK. ( 2 pt.
)
3. Suppose you took 1.00 mL of the KI solution from question #2 above and diluted it to
50.0 mL, what would be the concentration of the new solution? SHOW WORK. ( 2 pt.
)
4. 25.0 mL of 0.50 M solution of NaOH was diluted to a final volume of 200.0 mL. What is the new concentration of this solution? SHOW WORK. ( 2 pt.
)
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Procedure :
PART A. Preparing a 0.50 M copper (II) sulfate solution in a volumetric flask.
1.
Using your answer from prelab question #2, weigh out the required amount of copper (II)
sulfate in a clean, dry weighing boat.
2.
Bend the weigh boat inward diagonally and carefully pour the copper (II) sulfate into a 100mL volumetric flask. Use the wash bottle to rinse any solid remaining on the weighing boat and transfer into the flask. Add water to the flask until it is about half full.
3. Cap the flask and swirl it several times to dissolve ALL the solid. Do not shake the flask.
4. Slowly add water until the water level is near the etched line on the neck of the flask.
Add water drop-by-drop, until the bottom of the meniscus is on the etched line.
5. Cap the flask and invert the flask gently 7 to 10 times. Do not shake the flask.
6. Once the solution is thoroughly mixed, cap the flask to prevent contamination or evaporation. This is the 0.50 M CuSO
4
stock solution.
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PART B. Preparing Diluted Solutions of a Given Molarity.
1. Obtain 3 test tubes and place them into the test tube rack as test tubes 1, 2, & 3.
Pour 8-9 mL of your stock solution into a 10 mL graduated cylinder. Use a 1-mL pipet to add more stock solution drop-by-drop until the bottom of the meniscus is on the 10.0 mL mark of the cylinder. Pour the measured 10.0 mL of the stock solution into the 1 st test tube .
2. Using your answer from prelab question #3 , add this amount of your stock solution to the
10-mL graduated cylinder using the 1-mL pipet slowly until the bottom of the meniscus is on the mL mark of the cylinder that you need from prelab question #3.
3. Add water slowly, then drop-by-drop until the bottom of the meniscus is on the 10.0 mL mark of the cylinder. Pour this new solution into the 2 nd test tube .
This is 10.0 mL of a 0.250 M copper (II) sulfate solution.
4. Using your answer from prelab question #4 , add this amount of your stock solution to the
10-mL graduated cylinder using the 1-mL pipet slowly until the bottom of the meniscus is on the mL mark of the cylinder that you need from prelab question #4.
5. Add water slowly, then drop-by-drop until the bottom of the meniscus is on the 10.0 mL mark of the cylinder. Pour this new solution into the 3 rd test tube .
This is 10.0 mL of a 0.050 M copper (II) sulfate solution.
6. Compare the color of the stock solution and each of the dilutions in test tubes 1-3.
Rank these solutions in order of color intensity from the deepest blue to the lightest blue.
8. CLEAN UP:
After completing the data table, empty the test tubes into the sink with excess water.
Wash the test tubes and graduated cylinder with soap, water, and small test tube brushes.
Invert the test tubes and cylinder in the test tube rack so that they dry.
Wash the volumetric flask by adding a drop of soap and filling half-way with water.
Cover the end with your thumb, shake gently, empty, rinse, and repeat a few times without adding more soap. Finally rinse the flask with water until all soap is gone then invert on the drying rack.
Throw away the 1-mL plastic pipet and the plastic weighing boat.
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