Suitable for High School Physics/Chemistry
This test chamber can be used to quantify the resistance of any liquid (including ionic concentrations) over the given distance, with the use of an electric power pack and knowledge of Ohm's law.
Step 1: Construction of Test Chamber
For this construction you require:
- PVC piping
- PVC T-joint
- 3x PVC caps
- 2x Brass screws
- 4x Brass bolts
- 4x Zinc coated washers
- Silicon grease
1. The PVC piping should be cut to your desired length, and then assembled connecting to the T-joint, with a cap fitting on each of the 3 ends (the cap on the top of the T-joint is just for access into the chamber, so should be easily removed)
2. A small pilot hole is drilled into two of the caps and then the brass screws are screwed into the holes, with a washer and bolt of each side of the cap
3. Assemble the chamber and seal with silicon to prevent leakages
PVC piping was used as it is not conductive and would not affect the results. The electrodes (brass bolts and zinc coated washers) were galvanised, to reduce corrosion, alike to many typical liquid resistors. If the electrodes were to corrode, the distance between them would decrease, which would invalidate the results as resistance is measured over a constant distance.
Step 2: Experimentation
- Digital power pack
- Power chords with alligator clips
- Beaker filled with your desired liquid
- Fill test chamber with liquid
- Attach each power chords to an electrode of the test chamber
- Turn on power pack and measure the current at numerous voltages (about 5 trials)
Step 3: Calculations
According to Ohm's Law, you can calculate resistance by dividing voltage by resistance:
R = V / I
where R is resistance, V is voltage and I is current
Ohm’s law says that current is proportional to voltage and inversely proportional to resistance
Therefore, regardless of conventionally plotting the independent variable of the x-axis, and the dependant variable on the y-axis, the data could be graphed so that the gradient was equivalent to resistance. To do so, current was plotted on the x-axis and voltage on the y-axis.
Extension of experiment:
INVESTIGATE THE RELATIONSHIP BETWEEN IONIC CONCENTRATION AND RESISTANCE
With a deeper understanding of Ohm’s Law, the experiment could be redirected towards investigating the relationship between the concentration of an ionic compound and its resistance (various concentrations will need to be tested to determine the relationship). For an example, I tested the relationship between Copper (II) Sulphate concentration and resistance.
Solutions that contain dissolved ionic compounds (such as Copper (II) Sulphate) conduct electricity because they release charged particles into solution that are capable of carrying an electric current. Therefore, the current of ionic solutions increases as the concentration increases. This relationship can be described as Current is directly proportional to Ionic Concentration.
With the knowledge that current is inversely proportional to resistance, it can be concluded that Ionic Concentration is inversely proportional to Resistance
Collecting data using this experiment can be used to validate this claim.
This is an entry in the
Classroom Science Contest