The purpose of this experiment is to oxide ethanol a primary alcohol and then to test the product to determine whether it has been oxidised to ethanal an aldehyde: CH3CH2OH + [O] → CH3CHO + H2O

The Oxidation Of Ethanol

Introduction

The purpose of this experiment is to oxide ethanol a primary alcohol and then to test the product to determine whether it has been oxidised to ethanal an aldehyde:

CH3CH2OH + [O] → CH3CHO + H2O

Or whether it has been oxidised to ethanoic acid a carboxylic acid:

CH3CH2OH + 2[O] → CH3COOH + H2O

In theory, ethanal should be produced as a product. This is because you will be distilling the ethanal as it forms so it isn’t exposed to the acidified sodium dichromate to become a carboxylic acid. Therefore the CHO group of ethanal will not be oxidised further to the COOH group of ethanoic acid.

Observations

As the sodium dichromate and ethanol solution in the dropping funnel were slowly added to the concentred sulphuric acid in the pear shape flask, the colour of the solution gradually changed from orange to green as more of the dichromate and ethanol was added. This was because a reaction took place, so the dichromate – Cr2O72- got reduced to form chromium ions – Cr3+ and the ethanol got oxidised.

When the sodium dichromate and ethanol solution was added to the concentred sulphuric acid in the pear shape flask, I noticed that it began to bubble and out give out heat. This meant that there was an exothermic reaction between the acidified sodium dichromate and ethanol that caused it to continue boiling on its own.

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After the solution had been bubbling for a while a colourless distillate began to distil over the distillation funnel and was collected into a boiling tube which was held in a beaker with an ice and water mixture in so if the ethanal was produced, it didn’t just evaporate away because of its low boiling point.

When the 5 drops of the colourless distillate were added to the 5cm3 of 2, 4 dinitrophenylhydrazine to test for an aldehyde, within approximately 2 minutes an orange precipitate formed in the yellow/orange solution. This was because a carbonyl group was ...

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When 5 drops of the universal indicator were added to 5 drops of the distillate the colour of the universal indicator turned from green to pale green within the distillate. This meant that that pH value of the distillate was neutral so no acid group was present within distillate and confirms that the distillate was an aldehyde with no carboxylic acid present.

To make the experiment more reliable I also added saturated sodium carbonate solution to test for the presence of an acid group in addition to using universal indicator to test for an acid group. When it was added no bubbles were produced, normally if sodium carbonate was added to a solution that contained acid you would expect the sodium carbonate to react with the acid producing CO2 gas. The result of this test meant that there was no COOH group present which in turn told me that no ethanoic acid had been produced as the product.

Summary Of Tests

Risk Assessment

A lot of the chemicals used throughout the experiment are toxic to the environment and can cause long term adverse effects, therefore once used the chemicals will be left to the technicians to dispose of them safely.

I will wear eye protection throughout the whole experiment, so the likely hood of the any of the irritant or harmful chemicals getting into my eyes and harming them will be low.

Sodium dichromate

I am only using 5g of sodium dichromate when making it into a solution therefore there will be minimal risk of any of the dust from it entering my eyes. But to make certain none will enter my eyes I will still be wearing eye protection.
This chemical is very harmful if in contact with the skin, so when making up the sodium dichromate solution I will use a spatula so there is no question of the sodium dichromate irritating my skin and this way of handling the chemical will obtain maximum reliability.
Sodium dichromate is classed as a category 2 carcinogen and may cause cancer by inhalation, accordingly I will open the windows around the experiment so the laboratory will be well ventilated and none of the chemical will be inhaled.

Ethanol

The narcotic effect of ethanol is well- known and may result from inhalation of the vapour, therefore during the experiment I will endeavour not to take in any deep breaths.
Ethanol is highly flammable – the vapour can be ignited at temperatures above 13ºC so I will not light the Bunsen burner until I actually have to warm the solution in the pear shaped flask.

Sulphuric Acid

When diluting the 2cm3 of sulphuric acid with the 6cm3 of distilled water, I will add the acid drop at a time to the water in the pear shaped flask which will be held in a beaker full of ice because there is a very violent reaction between the two chemicals. A lot of heat is dissipated during the reaction so the ice in the beaker will cool the temperature down of the reaction. Furthermore, if all the acid is added to the water at the same time, the temperature would become so great that steam would be produced and acid in a vapour with it, which will be very hazardous as sulphuric acid is very corrosive and will burn your respiratory tract if inhaled.
Just in case any acid gets into a vapour, this part of the procedure will be performed in a fume cupboard so there will ventilation for the fumes to escape and again, eye protection will be worn to make sure none of the acid is splashed in my eyes.

Ethanal

This is an extremely flammable chemical therefore a small amount of ethanol will be used at the start, so not much of the ethanol will be oxidised to produce ethanal. In addition to this, the ethanal will be collected in a boiling tube which will be in a beaker full of an ice/water mixture which will lower the temperature of the chemical. This will minimise the risk of the ethanal catching alight.
Ethanal is classed as a category 3 carcinogen and has the risk of causing irreversible effects if inhaled. For that reason once all of the ethanal is collected, it will then be stored in a specimen tube within a fume cupboard.

Dinitrophenylhydrazine

This chemical is toxic by skin contact and stains skin yellow on contact which can lead to dermatitis. So to minimise contact with the skin I will use a pipette to dispense it into the boiling tube.

(Source: Cleapss Sheet 1995)