Transcript Solutions, Electrolytes, and Conductivity Lab 8 Purpose  The goal of this experiment is to illustrate the behavior of strong, weak, and non-electrolytes in.

Solutions, Electrolytes, and
Conductivity
Lab 8
Purpose
 The goal of this experiment is to illustrate the behavior of
strong, weak, and non-electrolytes in aqueous solution.
 This will be achieved through the use of electrical
conductivity measurements.
 You will be afforded more experience in solution
preparation.
Dissolution vs. Dissociation
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. You will
need the following values first:
 Molar mass of the solid
 Total volume desired
 Final concentration desired
Calculation:
 Mass, g = [ ], mol/L x MM, g/mol x Vol, L
 Remember the precision of your glassware!
Solution Preparation from Solids
 Make the solution:
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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.
You will need the following values first:
 Concentration of stock solution (M1)
 Desired concentration of diluted solution (M2)
 Desired volume of diluted solution (V2)
 Calculation:
 M1V1 = M2V2
 Remember the precision 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 glassware (usually a 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
 NaCl vs. C6H5COOH
Why?
Why?
Procedure
 Soak your conductivity probe in distilled water for 30 minutes
before starting your experiment. Why?
Conductivity, S/cm
Conductivity Standard
Distilled Water
0.0
0.004000 M KCl
578.0
0.008000 M KCl
1202.6
0.02000 M KCl
2949.6
0.04000 M KCl
5560.0
0.06000 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.
 Calibrate your conductivity probe.
 Measure the conductivities of your known solutions,
distilled water, tap water, and three unknowns.
Safety Concerns
 Reagents:
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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.
Acidic solutions need to be disposed in the acid waste
container in the fume hood.
Remember to clean up the balances and counters if /
when you spill anything.
Lab 9 Reminder
 Lab 9 is next.