1. Solutions, Electrolytes, and Conductivity
Lab 9
Solutions, Electrolytes, and Conductivity

2. Outline Purpose Solutions Solution Preparation from Solids
Solution Preparation from Liquids (dilution)
Electrolytes
Conductivity
Procedure
Waste
Skill Evaluation Reminder

3. Purpose
To illustrate the behavior of strong, weak, and non-electrolytes in aqueous solution.
Achieved through the use of electrical conductivity measurements.
Solution preparation practice.

4. Dissolution vs. Dissociation

5. Solutions Types of solutions we are dealing with today:
solid to liquid
liquid to liquid

6. Solution Preparation
When you are required to make a solution of accurate concentration, a volumetric flask is used.
We never make solutions of accurate concentration in:
Beakers
Graduated cylinders
Erlenmeyer flasks

7. Solution Preparation from Solids
Determine the mass of the solid needed by using:
Molar mass of the solid
Total volume desired
Final concentration desired
Calculation:
Mass, g = [ ], mol/L x MW, g/mol x Vol, L
Remember the tolerances on your glassware!

8. Solution Preparation from Solids
Make the solution:
Weigh out the appropriate mass of solid.
Place a small volume of distilled water in the volumetric flask.
Add the solid to the volumetric flask.
Add some more distilled water to the flask, stopper, and invert several times.
Add distilled water to the calibration line (fill to volume) using a medicine dropper, stopper, and invert several times.

9. Solution Preparation from Liquids
Determine the volume of stock solution needed by using:
Concentration of stock solution (M1)
Desired concentration of diluted solution (M2)
Desired volume of diluted solution (V2)
Calculation:
M1V1 = M2V2
Remember the tolerances of your glassware!

10. Solution Preparation from Liquids
Make the solution:
Obtain the appropriate volume of stock solution using a graduated cylinder. (Always add a few mL extra.)
Place a small volume of distilled water in a volumetric flask.
Use the appropriate pipet to transfer the correct volume of stock solution from the graduated cylinder to the volumetric flask.
Add some more distilled water to the flask, stopper, and invert several times.
Add distilled water to the calibration line (fill to volume) using a medicine dropper, stopper, and invert several times.

11. Electrolytes Strong Electrolytes
100% dissociation and high conductivity
NaCl(s)  Na+(aq) + Cl-(aq)
Weak Electrolytes
partial dissociation and partial conductivity
CH3COOH(aq)  CH3COO-(aq) + H+(aq)
Non Electrolytes
no dissociation and no conductivity
C12H22O11(s)  C12H22O11(aq)

12. Conductivity
The ability of an aqueous solution to conduct electricity is dependent on the presence of ions in solution.
Conductivity or K has units of S/cm, mS/cm, or S/cm.
We measure conductivity so we can make a comparison regarding relative numbers of ions present in solution.

13. Conductivity
The extent to which a solution conducts electricity is dependent on the proportional amount of ions present in solution.
Which of the following will have a higher conductivity?
NaCl vs. CaCl2 Why?
NaCl vs. C6H5COOH Why?

14. Procedure Conductivity Standard Conductivity, S/cm Distilled Water
Soak your conductivity probe in distilled water for 30 minutes before starting your experiment. Why?
Calibration
Conductivity Standard
Conductivity, S/cm
Distilled Water
0.0
M KCl
578.0
M KCl
1202.6
M KCl
2949.6
M KCl
5560.0
M KCl
8426.9

15. Procedure
Any glassware that will be containing non-electrolytes or weak electrolytes need to be rinsed thoroughly with distilled water prior to use!!!
Make up your three known solutions.
Measure the conductivity of your known solutions, distilled water, tap water, and three unknowns.
The unknowns are already at the required concentration. No dilution is necessary!

16. Safety Concerns Reagents: Eye Contact: Skin Contact: Inhalation:
Acetic Acid (3%)
KCl
NaCl
Sucrose
Eye Contact:
Irritation, redness, pain, and possible damage
Skin Contact:
Irritation. May cause sensitization and / or allergic reaction. Absorption may cause symptoms similar to ingestion
Inhalation:
Irritation and coughing
Ingestion:
Gastrointestinal irritation, nausea, vomiting, diarrhea, prostration, dehydration and congestion of internal organs, and violent inflammatory reactions in the gastrointestinal tract

17. Waste
All neutral solutions can go down the drain with plenty of water when you are finished. Solutions with a pH above 8 or below 6 need to go in the acid / base waste container in the fume hood.

18. Next Week - Skill Evaluations
Read through pages 281 – 300.
Remember to bring your goggles and lab manual.