# Solutions, Electrolytes, and Conductivity

## Presentation on theme: "Solutions, Electrolytes, and Conductivity"— Presentation transcript:

Solutions, Electrolytes, and Conductivity
Lab 9 Solutions, Electrolytes, and Conductivity

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

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.

Dissolution vs. Dissociation

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

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

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!

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.

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!

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.

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)

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.

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?

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

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!

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

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.

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