Conductivity of Solution Testing

Introduction:

Some compounds contain ions. We can test for this condition by dissolving a compound in water. If the compound contains ions, the ions will be dispersed throughout the water and free to move. The movement of the ions in a solution enables them to conduct a current.

Substances that conduct an electric current when dissolved or melted are called electrolytes. Electrolytes contain moveable ions. The moveable ions carry the electric charge through the solution thus creating an electric current. The electric current, if sufficient enough, will light one of both of the LEDs. Examples of electrolytes include sodium chloride solution, tap water, dilute acetic acid, and hydrochloric acid. These compounds contain ionic bonds. Tap water contains dissolved Ca⁺², Fe⁺², SO₄^-2 and OH^- ions

Substances that do not conduct an electric current are called non-electrolytes. Non-electrolytes do not ionize; they do not contain moveable ions. The LEDs will not light since there are no ions to carry the electric charge. Examples of non-electrolytes include sugar solution, ethyl alcohol, glycerin, distilled water.

Objective: To observe the conductivity of electrolytes.

To determine the type of bonding that occurs in solutions that conduct a current.

Safety: Wear goggles

Materials:

Conductivity Apparatus hydrochloric acid sodium chloride crystals

Tap water sugar

Distilled water ethyl alcohol beakers

Sodium chloride

Procedure:

1. Make sure the two copper electrodes are parallel to each other and not touching.

Half-fill all beakers except # 7 with distilled water;

2. Label each beaker as follows and add to it:

Beaker 1 nothing

Beaker 2 spoonful of sugar

Beaker 3 spoonful of sodium chloride

Beaker 4 10 ml 0.10 M HCl

Beaker 5 10 ml 10 % acetic acid

Beaker 6 10 ml ethyl alcohol

Beaker 7 NO DISTILL WATER- add 50 ml tap water

3. Wash the electrodes with distilled water into an empty 400 ml beaker between each testing. Dry the electrodes with a tissue before testing.

4. Turn on the conductivity apparatus; dip the electrodes into the substance to be tested.

5. Observe the brightness of BOTH the red and green LEDs; compare to the conductivity scale printed on the back of the conductivity apparatus (see table below). The brightness is best observed by looking at the LEDs straight on.

6. Turn off the conductivity apparatus. Rinse with distilled water and dry the electrodes before testing the next sample or storing the conductivity apparatus.

Scale	Red LED	Green LED	Conductivity
0	Off	Off	Very Low or none
1	Dim	Off	Low
2	Medium	Off	Medium
3	Bright	Dim	High
4	Very bright	Medium	Very high

Data Analysis:

Make a table in your lab book:

Solution

Conductivity

Type of bonding (ionic or covalent)

Conclusions:

1. How are the compounds that caused the bulb to light similar to one another?

2. What type of bonding causes a solution to conduct an electric current? Why

3. Did tap water conduct an electric current? Why or why not?

4. True or False: The reason a compound did not cause the bulb to light is because the substance did not dissolve in water. Explain your answer.

5. Which solution conducted the most current? If you filled the beaker with distilled water to the brim, would your results be the same? Why or why not.