Science Project Details:

The effect of water salinity on electrolysis

Difficulty: Advanced 8
Cost ($): 30
Time required: < 1 day
1 hour to prepare, 1 hour for experiment
Availability of materials:
May be purchased from a hobby store, or alternatively obtained from a school science laboratory
Required Skills:
Using voltmeters/ammeters
Safety concerns:

1. Use only batteries. NEVER connect to a mains supply.
2. Conduct the experiment under supervision of a qualified person (science teacher). Flammable gasses may be released.
3. Electrolysis of sea water may produce chlorine gas. Take necessary precaution. Ensure that the experiment is conducted in a well-ventilated laboratory

Abstract

This experiment was done to investigate how the salinity of water affects the electrolysis process. Comparison was made between ocean water and distilled water.

Hypothesis

Sea water with higher salinity will conduct more electricity.

Background

Electrolysis process

Electrolysis is the process where electric current passes through a solution. The process requires a voltage source, an anode (positive) electrode, a cathode (negative) electrode and an electrolyte solution.

The electrolysis process will start when the positive terminal of a battery is connected to the anode and the negative terminal of the battery is connected to the cathode. When this connection is done, the positive ions in the electrolyte will move towards the cathode and the negative ions will move towards the anode resulting in current flow.

Water by itself is a poor conductor. But if salt or sodium chloride is added to water, it can start to conduct electricity through the electrolysis process.

Sodium chloride in solid form does not conduct electricity. The electrostatic attraction between the sodium ion and chloride ion is very strong when it is in solid form. However when sodium chloride is mixed in water, the sodium and chloride ions are separated and move freely in the solution making it a good electrolyte.

Scientific Terms

Electrolysis, electrolyte, ions, electrodes, anode, cathode, sodium chloride

Materials

The materials required for this science fair project:
- 2 beakers
- 300ml distilled water
- 300ml sea water
- 2 copper electrodes (either a copper rod, copper bar or copper wire)
- 4  1.5V batteries
- Battery holder
- 4 jumper wires with crocodile clips at both ends
- A digital voltmeter
- An ammeter
- A small light bulb with socket

Procedure

1. For this experiment, the independent variable is the use of seawater or distilled water. The dependent variable is the amount of current flowing in the circuit as indicated by the bulb lighting up, and the brightness of the bulb. This is measured by using the ammeter to measure the current and observing the light bulb. The constants (control variables) are the battery voltage, light bulb wattage and the amount of electrolyte solution used.

2. Label the beakers as  A and  B. Fill beaker A with 300ml of distilled water and beaker B with 300ml of salt water.

3. Place both copper electrodes in beaker A. The electrodes must not touch one another. Connect one jumper wire from the battery to one of the copper electrodes. The other wire from the battery is connected through the light bulb and ammeter to the second electrode in the beaker. Once the connection is done, the electrolysis process will begin. Please refer to figure 1 for the circuit connection. The voltage can be measured using the digital voltmeter between the electrodes.

electrolysis science fair project

4. Observe the light bulb, ammeter readings and voltmeter readings and record the observations in the table given below.

5. Repeat procedures 3 and 4 using the seawater in beaker B and record the observation and readings in the table below.

Observation

The results show that the bulb will light up when sea water is used but does not light up when distilled water is used. The current measured was also higher for sea water. However the voltage measured was almost the same for both electrolyte solutions.

Electrolyte Solution

Voltmeter (V)

Ammeter (A)

Light bulb

Distilled water

5.95

0.01

Not lighted

Sea water

5.85

0.12

Lighted up

Conclusion

The hypothesis that  sea water with a higher salinity will conduct more electricity is proven to be true. The presence of salt in seawater  makes it a good conductor.

Electrolysis process can be used to store energy and reproduce it for later use. Examples are the rechargeable and disposable batteries and batteries used to start cars. Currently environment friendly energy sources like solar panels and wind turbines make use of batteries to store the energy that they produce for later use.

Also consider

The experiment can also be done by varying the amount of salt in the water.

This experiment can also be repeated to observe the effect of different sizes and types of electrodes.

References

Electrolysis - http://en.wikipedia.org/wiki/Electrolysis

Electrolysis - http://www.tutorvista.com/content/chemistry/chemistry-iii/redox-reactions/electrolysis.php     

Electrolysis - http://www.educationalelectronicsusa.com/c/electrolysis-I.htm

Video(s)