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Investigation into the Properties of Covalent Substances – Chemistry IAA

The Chemistry IAA experiment is a big complicated which is why it is explained in this article very clearly. The IAA investigates the properties covalent substances have, in this case, we will be using urea, glucose and salol as the covalent substance. As this IAA exam is 10% of a GCSE in science, it is extremely important to master this exam.

Firstly, let’s identify what the independent and dependant variables are:

Independent Variable – Number of carbon atoms
Dependant Variable – Melting point of substance

Independent variable causes a change in Dependent Variable and it isn’t possible that Dependent Variable could cause a change in Independent Variable. So, the number of carbon atoms causes a change in the melting point.

  • Graphite rods x2
  • Wires x4
  • Crocodile clips x2
  • 1 set of batteries 
The circuit required in this experiment
1) Set up a complete circuit as in the diagram.
2) Check that the wires and batteries work by touching the graphite rods together. If the light does not come on, then replace components in the circuit till it does.
3) Place the graphite rods into a solid sample to be tested, ensuring that the rods do not touch.
4) Record whether the bulb lights up or not.
5) Repeat this for each substance.

Diagram showing graphite rods in
sample solution

6) Dissolve 2 spatulas of substance in distilled water.
7) Place the graphite rods into the water and record whether or not the bulb lights.
8) Repeat this for each sample, being careful to avoid cross contamination.

9) Add 200ml of distilled water to a 250ml beaker.
10) Take a small sample of your substance and place in a test tube.
11) Place the test tube in the beaker of water and then heat very slowly on a blue flame, ensuring that the water is constantly stirred.
12) Record the temperature to 1 decimal place when the sample first starts to melt.
13) Repeat two further times.
14) Throughout the whole experiment, ignore any anomalous data and repeat to compensate.

As you can’t produce a very good graph, you can only produce a table and it should look something like this:

Pattern from the Table
From the table, it is clear than urea and glucose cannot conduct as a solid or as a solution. This is because covalent bonds haven’t got any spare electrons to have a flow of charge. From heating salol up, the melting point of the substance is 41.5 degrees. This shows that covalent bonds are quite strong and require some energy to break them.

The method was and could have been made more valid by (The point/Explanation for the point)
Using same amount of substance so that each substance has same amount of energy applied to each particle
Use same circuit to stop mistakes from happening
Same graphite rods so there is always same conductivity
Same voltage in circuit otherwise the bulb may light due to extra voltage
Same bulb otherwise results may differ from the light intensity changing from the bulb
Same amount of water so concentration of substance in water is the same

The method was made reliable by
Checking that the circuit works
Repeat the individual experiments (1-5) (6-8) and (9-13)
By heating the substance very slowly
Recording temperature to 1 decimal place
Ignore anomalous date and repeat to compensate
Using distilled water as normal water has potassium and magnesium in it which makes it conduct electricity

(this is where you should use your results and scientific knowledge)
Ultimately, urea, glucose and salol didn’t conduct as a solid neither as a liquid. However, we found that the melting point of salol was 41.5 degrees. This shows that covalent bonds don’t conduct electricity. This is because covalent substance (with exception to graphite) share electrons between atoms and therefore don’t have free electrons. This makes the substances not have a flow of electrons therefore charge.



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