Transcript Lab 9 Solutions, Electrolytes, and Conductivity Purpose • To illustrate the behavior of strong, weak, and nonelectrolytes in aqueous solution. • Achieved through the use.

Lab 9
Solutions,
Electrolytes, and
Conductivity
Purpose
• To illustrate the behavior of strong, weak, and nonelectrolytes in aqueous solution.
• Achieved through the use of electrical conductivity
measurements.
• Solution preparation practice.
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:
oBeakers
oGraduated cylinders
oErlenmeyer flasks
Solution Preparation from
Solids
• Determine the mass of the solid needed by using:
o Molar mass of the solid
o Total volume desired
o Final concentration desired
• Calculation:
o Mass, g = [ ], mol/L x MW, g/mol x Vol, L
o Remember the tolerances on your glassware!
Solution Preparation from
Solids
• Make the solution:
o
o
o
o
o
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:
o Concentration of stock solution (M1)
o Desired concentration of diluted solution (M2)
o Desired volume of diluted solution (V2)
• Calculation:
o M1V1 = M2V2
o Remember the tolerances of your glassware!
Solution Preparation from
Liquids
• Make the solution:
o Obtain the appropriate volume of stock solution using a graduated cylinder.
(Always add a few mL extra.)
o Place a small volume of distilled water in a volumetric flask.
o Use the appropriate glassware (usually but not always the pipet) to transfer the
correct volume of stock solution from the graduated cylinder to the volumetric
flask.
o Add some more distilled water to the flask, stopper, and invert several times.
o 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?
o NaCl vs. CaCl2
o NaCl vs. C6H5COOH
Why?
Why?
Procedure
• 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
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 nonelectrolytes 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!
• Reagents:
o
o
o
o
Safety Concerns
Acetic Acid (3%)
KCl
NaCl
Sucrose
• Eye Contact:
o Irritation, redness, pain, and possible damage
• Skin Contact:
o Irritation. May cause sensitization and / or allergic reaction. Absorption
may cause symptoms similar to ingestion
• Inhalation:
o Irritation and coughing
• Ingestion:
o 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.
• All skills covered to date are fair game.
• Remember to bring your goggles and lab manual.