Introduction
For today's practical session, the aim was to find out if the different substances were oxidising or reducing agents. For this test, we used:
- Aqueous potassium manganate (VII) --> Used to test for reducing agent
- Aqueous potassium iodide --> Used to test for oxidising agent
- Dilute sulfuric acid
- Solids P and Q, and solutions R and S
Procedure
- Prepare solutions of substances P and Q by transferring half a spatula of each substance in separate test tubes and dissolving half a test tube of distilled water. Divide the solutions of P and Q into two portions to be used for Test 1 and 2 respectively.
- For Test 1, add 1cm^3 of dilute sulfuric acid to each solution. Then add KMnO4 solution.
- Test 1 is testing for the presence of reducing agents. A positive test will involve a change in colour of solution from purple to colourless.
- For Test 2, add 1cm^3 of dilute sulfuric acid to each solution. Then add KI solution.
- Test 3 is testing for the presence of oxidising agents. A positive test will involve a change in colour of solution from colourless to brown.
- Record your observations in a table as shown below.
Observations
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| Solution S, Test 2: Brown solution (left) from original colourless solution (right) |
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| From left to right: Solution P test 1 and 2, Solution R test 1 and 2 |
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| Close up of dark brown solution when KI is added to solution P. |
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| Close up of purple solution when KMnO4 was added to solution P. |
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| It is important to first add your sulfuric acid, otherwise your results would look something like that. |
Conclusions
P is an oxidising agent based on the results from test 2.
Q is a reducing agent based on the results from test 1.
R is unreactive based on the results from both tests.
S is disproportionated based on the results from both tests.
