Expt 035 -- Electrical Conductivity

Description

The electrical conductivities of solutions of strong electrolytes, weak electrolytes, and nonelectrolytes are studied.

Background

Safety

Toluene and ethanol are flammable. Keep flames and other ignition sources 10 feet (3 m) away from the flammable chemicals; provide adequate ventilation. Toluene, ethanol, and ammonia are toxic. Other substances tested also may be toxic. Wear goggles and apron. Avoid ingesting or inhaling chemical substances. Wash spills immediately with large amounts of water. Wash hands after the experiment.

Procedure

  1. Test the conductivity of each of the following liquids: distilled water; toluene; 0.1 M sodium chloride (sodium sulfate, potassium chloride); sugar; acetic acid; and ammonia.
    !!!Click here to See Movie.
  2. Make sure the distance between the electrodes is not changing while you make measurements. Wash thoroughly
  3. Record the results in the table.
    1. Water
      !!!Click here to See Movie.
    2. 0.1M NaCl
      !!!Click here to See Movie.
    3. 0.1M Na2SO4
      !!!Click here to See Movie,
    4. Toluene
      !!!Click here to See Movie.
    5. Sugar
      !!!Click here to See Movie.
    6. 5% acetic acid
      !!!Click here to See Movie.
  4. Use a plastic transfer pipet to remove the toluene from the well and discard it into the disposal jar placed under the hood. Rinse the remaining wells into the sink. Wash the strip with water.
  5. Place some 1 M NaCl in the first well of a 12-well strip. Prepare a series of 1 to 5 dilutions from this well. Place 8 drops of distilled water in wells 2 through 12 using a plastic transfer pipet with a restricted tip as a dropper. Empty this dropper. Use the plastic pipet dropper to remove 2 drops from well 1 and place in the second well. Mix using the dropper. Remove 2 drops from this well and add to the third well. Mix. Continue in this fashion for all of the wells. Test the conductivity of each well. Wells tested will be 1M, 0.2M, 0.04M, 0.008M, etc. Note and record changes.
    !!!Click here to See Movie. Movie corresponds to 1M.
    !!!Click here to See Movie. Movie corresponds to 0.2M.
    !!!Click here to See Movie. Movie corresponds to 0.008M.

Questions

  1. Would copper metal be classified as a strong electrolyte, weak electrolyte, or nonelectrolyte. Explain.
  2. Classify methanol as a strong electrolyte, weak electrolyte, or nonelectrolyte.
  3. Explain why the distance between the electrodes in the conductivity probe is kept constant.

Handout Makeup

Name ___________________________ Class _______

Teacher __________________________

SmallScale 035 Electrical Conductivity

Watch the movies and record your observations below.

Classify each solution as a non-, strong, or weak electrolyte.

Water
0.1M NaCl
0.1M Na2SO4
Toluene
Sugar
5% acetic acid
1M NaCl
0.1M NaCl
0.008M NaCl

Note any other observations.

Answer the questions

  1. Would copper metal be classified as a strong electrolyte, weak electrolyte, or nonelectrolyte. Explain.
  2. Classify methanol as a strong electrolyte, weak electrolyte, or nonelectrolyte.
  3. Explain why the distance between the electrodes in the conductivity probe is kept constant.

Curriculum-

Use when discussing solutions or when discussing types of bonds, since ionic materials using are strong electrolytes in solution.

Safety-

Toluene and ethanol are flammable. Keep flames and other ignition sources 10 feet (3 m) away from the flammable chemicals; provide adequate ventilation. Toluene, ethanol, and ammonia are toxic. Other substances tested also may be toxic. Wear goggles and apron. Avoid ingesting or inhaling chemical substances. Wash spills immediately with large amounts of water. Wash hands after the experiment.

Time-

Teacher Preparation: 10 minutes if apparatus is being reused.

Class Time: 30 minutes

Materials-

Disposal-

Lab Hints-

Answers-

Q1. Would copper metal be classified as a strong electrolyte, weak electrolyte, or nonelectrolyte. Explain.
A1. Metallic conductors usually are not characterized using these terms. These terms are reserved for electrolytic conductors that use ions in solution as the charge carriers.
Q2. Classify methanol as a strong electrolyte, weak electrolyte, or nonelectrolyte.
A2. Methanol, like ethanol, is a nonelectrolyte.
Q3. Explain why the distance between the electrodes in the conductivity probe is kept constant.
A3. The longer the distance traveled by the current, the higher the resistance. The space between electrode is kept constant to control for this distance factor.

Handout Ans.-

Record the results in the table.

Water- nonelectrolyte
0.1M NaCl- strong electrolyte
0.1M Na2SO4- strong electrolyte
Toluene- nonelectrolyte
Sugar- nonelectrolyte
5% acetic acid- weak electrolyte
1M NaCl- strongest electrolyte
0.1M NaCl- strong electrolyte

Others not shown in movies

CoopLearn-

Assigning large numbers of nontoxic substances to different students or student groups and pooling testing data is appropriate.

Reference-

The small scale version of this lesson was developed by Steve Wignall, Seward, NE. It was developed at an EESA workshop at Lincoln East HS, Lincoln, NE, in 1988.

Key Words 1-

electrolyte, strong electrolyte, weak electrolyte, non-electrolyte, electrode, conductor, insulator, conductivity

Elements-

C N O H Na Cl S