Make multiple dilutions and use conductivity as a proxy for concentration

PART A. Preparing a 1.0 M Sodium Chloride solution in a volumetric flask.

1. Calculate the mass of Sodium Chloride required to make 20.0 mL of a 1.0 M

solution. Measure out the required amount of solid NaCl into a new plastic

weighing boat.

2. Transfer the NaCl into a 20 mL volumetric flask, using a wash bottle to rinse any

solid remaining on the weighing boat. Add water to the flask until it is one-half to

two-thirds full.

3. Cap the flask and invert the flask gently several times until the solid dissolves

completely. Use your thumb or forefinger to secure the cap onto the flask while

inverting. Do not shake the flask hard as the glass neck may break.

4. Continue (slowly) adding deionized water until the water level is near the etched

line on the neck of the flask. Add water more carefully, drop-by-drop, until the

bottom of the meniscus is on the etched line.

5. Cap the flask and invert the flask gently 3 to 4 more times. Do not shake the flask

hard as the glass neck may break.

6. Once the 1.0M solution of Sodium Chloride is thoroughly mixed and all solid has

been dissolved, transfer it to a labeled, clean, dry beaker.

PART B. Making diluted solutions of difference concentrations from the stock solution.

**You will need to get a Labquest device fitted with a conductivity probe for this part**

1. Using the equation C1 X V1 = C2 X V2 solve for the volume of stock solution you

will need to use to make 100mL of 0.0075M NaCl solution. Once you know the

volume of stock solution you will need to pipette, obtain a P-1000 micropipette

with the appropriate disposable tip. Use the pipette to transfer the necessary

volume of stock solution into a clean, dry 100mL volumetric flask. Fill the flask to

the etched line with deionized water, taking care not to go past the 100mL line.

2. Pour this 0.0075M NaCl solution into a clean, dry beaker (150, 200, or 250mL

beaker should be fine).

3. Use the Labquest hand-held device fitted with a conductivity probe to measure

the conductivity of this solution. Record this value.

4. Dispose of the dilute solution following your instructor’s directions. Clean and dry

the 100mL volumetric flask and small beaker.

5. Repeat steps 1 through 4 to make a 0.005M NaCl solution, be sure to record the

conductivity value.

6. Repeat steps 1 through 4 again to make a 0.0025M NaCl solution, be sure to

record the conductivity value.