- The smell of the product
- Adds an appreciable volume of sodium carbonate solution
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Add a few drops of the product to 2 cm3 of Benedict’s solution and 1 cm3 dilute sodium hydroxide, then boil gently.
The partial oxidation of propan-1-ol
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Place about 10 cm3 of dilute sulphuric acid in a flask and add about 3 g of sodium dichromate(VI) and 2 or 3 anti-pumping granules.
- Shake the contents of the flask until solution is complete.
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Add 1.5 cm3 of propan-1-ol in drops from a dropping pipette, shaking the flask so as to mix the contents, and then assemble the apparatus as shown in the diagram.
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Gently and slowly distil 2 cm3 of liquid into a test tube.
- Carry out the tests 11a, b and c above, comparing the results.
Diagram:
Results:
Dehydration of propan-1-ol:
- Bromine water has been decolourised.
- Potassium manganate changes from purple to brown.
Oxidation of propan-1-ol:
- There is a smell of vinegar.
- When sodium carbonate is added, the solution fizzes. The solution turns from acidic into neutral when the fizzing stops.
- While heated, Benedict’s solution has not turn colour.
Partial oxidation of propan-1-ol:
- There is a pungent smell.
- No bubbles made while adding sodium carbonate. It quickly turns universal indicator into dark blue in colour.
- Benedict’s solution turns from pale blue into orange precipitate.
Analysis:
Dehydration of propan-1-ol:
The gas produced turns bromine water from brown into colourless. This means that this is a gas which contains double bonds (alkenes). As only water is removed, we get from propan-1-ol (CH3CH2CH2OH) into CH3CH2CH, which is also equal to propene. So the product we got is propene gas. It also turns potassium manganate from purple to brown, so it means that it is a reducing agent.
Oxidation of propan-1-ol:
There is a smell of vinegar. That states that this is a carboxylic acid (functional group COOH). Given that we have propan-1-ol as our starting agent, the carboxylic acid should be propanoic acid. When sodium carbonate (an alkaline) is added to the carboxylic acid, a gas has been produced. Neutralization has taken place, so the gas made has to be hydrogen. Benedict’s solution has not changed colour, so there is no reducing sugar present in the product.
Partial oxidation of propan-1-ol:
There is no gas produced when sodium carbonate is added. This shows that there is no acid present in the partially oxidized product. It also turns Benedict’s solution from pale blue to orange precipitate. This means that a reducing sugar is present.
Conclusion:
The gas produced when propan-1-ol is dehydrated is propene. It is a reducing agent.
The oxidation of propan-1-ol will create propanoic acid.
The partial oxidation of propan-1-ol will create a substance which reacts with sodium hydroxide to form a reducing sugar.
Evaluation:
This is an experiment about propan-1-ol which is done in three separate parts. In each part I encountered problems.
For the dehydration experiment, I managed to collect four tubes of gas successfully. But for the first tube, it contains few product gas, as the gas does not fully turned bromine water to colourless. It is because most of the gas is air from the tube. Air expanded quickly in the boiling tube and got delivered to the other tube which I use to collect gases. If I am to collect more products in the tubes, I have two solutions. One is let air expand for some time, and start collecting gas after all the expanded air is pumped out. The other way is to collect a fifth or even sixth tube of gas, and discard the first and second tubes as they might contain air in it. By this I can obtain a purer product.
The oxidation was pretty successful. I did not come across a problem while mixing the reactants, or putting the pear-shaped flask in the right place. But one problem I see is that the reactants in the flask quickly boils. For a few times it almost spill out of the flask and contaminate my product. But I quickly fixed this problem by controlling the flame better (taking it a bit further away from the flask).
The partial oxidation of propan-1-ol was a complete failure. The results I used above were from another student. I did not manage to get the expected product. Instead, I got something which is slightly acidic (as it turns universal indicator red at the first place). Then it did not contain any reducing sugar after I added sodium hydroxide and heat it. All I got was a very similar product as the complete oxidation of propan-1-ol. Until now, I am still unable to find out what the problem is. In order not to make the same mistake again, I will be more careful in doing this experiment. Use very accurate apparatus to measure volumes in order to avoid random errors. Cleanse every apparatus I use thoroughly before I start my experiment, in order to eliminate systematic error.
