Conductivity Lab (Old)

Purpose (put into lab book)

• The purpose is to examine how the concentration of an acid affects the conductivity of the acid. We will also determine which acids are better at conducting electricity.

Background (read the following information then answer the questions in complete sentences in your lab notebook)

In this experiment, you will examine acids and how well they conduct electricity. An electrolyte is a substance that, when dissolved in water, conducts electricity. Acids and bases conduct electricity, therefore, acids and bases are one type of electrolyte.

You will examine conductivity using a conductivity probe. Conductivity is the ability to conduct electricity. Acids are hydrogen compounds dissolved in water. When they dissolve, they ionize (break into ions). Ions are what give a solution the ability to conduct electricity. When the probe is placed in a solution that contains ions, an electrical current is complete across the electrodes that are located on either side of the hole near the bottom of the probe. This results in a conductivity value that can be read by the computer. The unit of conductivity used in this experiment is μS/cm.

The size of the conductivity value depends on the ability of the aqueous solution to conduct electricity. Strong electrolytes produce large numbers of ions, which result in high conductivity values. Weak electrolytes result in low conductivity values because they have only a small number of ions present in the solution. Non-electrolytes should result in no conductivity. In this experiment, you will examine a strong acid (hydrochloric acid) and a weak acid (acetic acid) and determine their ability to conduct.

1. What is an electrolyte?

2. Do acid and bases conduct electricity?

3. What is conductivity?

4. What device will you be using to measure the conductivity of the acid?

5. What happens to acids when they dissolve?

6. What gives solutions the ability to conduct electricity?

7. What unit is conductivity measured in for this experiment?

8. What kind of electrolytes produce large numbers of ions?

9. What kind of electrolytes produce a small number of ions?

10. What two acids are we testing in this experiment?

Hypothesis (answer in complete sentences in lab book)

• 1. Which acid do you think will have a higher conductivity, hydrochloric acid or acetic acid?

1. How do you think the conductivity will be affected as the concentration of the acids is decreased?

Materials (put in lab book)

• Read the procedure below and list all of the materials required to complete this part of the lab. Do not forget to include chemicals and glassware.

Procedure

(Read Part 1 and draw a diagram explaining what you will be doing. - SHOW ME BEFORE MOVING ON!)

Part 1 - Preparing Diluted Solutions: FOLLOW DIRECTIONS CAREFULLY!!

(one lab group will do HCl, the other lab group across from you will do HC₂H₃O₂)

• 1. Measure out 100mL of 0.5 M HCl (or HC₂H₃O₂) and put it in the 0.5 M labeled beaker.

1. Take that beaker labeled 0.5 M from step 1 and measure out 20mL of that 0.5 M acid. Fill the 100mL graduated cylinder the rest of the way with water (80mL) and pour it all into the beaker labeled 0.1 M.

2. Now take the beaker from step 2 labeled 0.1 M and measure out 20mL of that 0.1 M acid. Fill the 100mL graduated cylinder the rest of the way with water (80mL) and pour it all into the beaker labeled 0.02 M

3. Now take the beaker from step 3 labeled 0.02 M and measure out 20mL of that 0.02 M acid. Fill the 100mL graduated cylinder the rest of the way with water (80mL) and pour it all into the beaker labeled 0.004 M.

4. STOP HERE AND MAKE THE SOLUTIONS FOR PART 1. WHEN YOU ARE FINISHED CONTINUE ON TO PART 2.

(Read Part 2 and draw a diagram explaining what you will be doing. - SHOW ME BEFORE MOVING ON!)

Part 2 - Measuring the Conductivity of Each Solution:

1. Hook up the conductivity probe to the computer and open LoggerPro.

2. Make sure the conductivity probe's switch is set to the range of 0-20000 μS.

3. Line the HCl (or HC₂H₃O₂) solutions up from highest to lowest concentration according to molarity.

4. Click the green collect button towards the middle of the tool bar of LoggerPro.

5. Dip the probe into the highest concentration solution and hold for 15 seconds.

6. Move it to the next solution and repeat all the way to the lowest concentration solution.

7. When you have gone through each HCl (or HC₂H₃O₂) solution hit the red stop button located towards the middle of toolbar in LoggerPro.

8. Autoscale your graph.

9. Using your mouse, highlight the first plateau of your graph.

10. On the top toolbar click "Statistics" and a box will appear. Record the max value given in the box.

11. Repeat for each plateau.

12. Now trade the solutions you prepared with the other side of the desk and measure the conductivity of their solution.

Data (put into lab book)

Click here if you're absent to see pictures from lab.