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To Identify Bio Chemicals in an Unknown Substance Essay Sample

essay
  • Pages: 2
  • Word count: 481
  • Rewriting Possibility: 99% (excellent)
  • Category: experiment

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Introduction of TOPIC

The object of the experiment is to test a substance and identify the bio chemicals, which exist in that substance.

Food tests are used to identify which bio chemicals exist in a substance. The substances characterised are in the tests are:

carbohydrates, starch, lipids and peptide bonds.

Method:

The following tests were used to identify the relevant substances:

Benedicts Test

Carbohydrates – reducing sugars such as glucose fructose and maltose

* Add 2cm3 of a solution to a test tube.

* Add an equal volume of Benedicts solution.

* Shake and bring gently to the boil, shaking continuously to minimise spitting.

Red brown precipitate result indicates reducing sugars present

Disaccharide hydrolysis test and Benedicts test

Carbohydrates – non-reducing sugars such as sucrose

* Add 2cm3 of solution to a test tube .

* Add 1cm3 dilute hydrochloric acid.

* Boil for one minute.

* Carefully neutralise with sodium hydrogen carbonate

* Carry out Benedicts test

Brick red precipitate indicates reducing sugars present, if above test is negative

Heavier precipitate indicates reducing sugars present. if above test is positive

Star

ch Test Starch * Add 2cm3 1% solution to a test tube * Add a few drops of I2/KI

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solution.

A blue-black colouration indicates starch present

To Identify Bio chemicals in an unknown substance

Method

Lipids Test

Lipids such as oils, fats and waxes.

* Add 2cm3 of absolute ethanol to a test tube

* Add 2cm3 of solution to the test tube

* Dissolve the solution by shaking vigorously

* Add an equal volume of cold water

A cloudy white suspension indicates lipids are present

Biuret Test

Add 2cm3 of solution to a test tube

Add an equal volume of 5% potassium hydroxide solution and mix

Add 2 drops of 1% copper sulphate solution and mix

A mauve or purple colour indicates peptide bonds are present

Results

Benedicts test

An unknown substance was tested and the test results were as follows:

Benedicts test – reducing sugars

As the solution was heated the substance changed from a brown to a light orange solution indicating a positive test.

Disaccharide hydrolysis test and Benedicts test

After boiling the litmus paper was dipped into the solution to check the Ph. The Ph turned red indicating a Ph of 1. Sufficient sodium hydroxide was added until the litmus paper turned olive green indicating a neutralised solution.

The Benedict’s test was carried out on the neutralised solution. The solution turned orangey red after heating, indicating a positive result.

Starch test

After the I2/KI solution was added there was no change to the substance it did not have a blue-black colouration indicating a negative result.

To Identify Bio chemicals in an unknown substance

Results

Lipid test

After dissolving the solution in ethanol a cloudy white suspension did not form, indicating a negative result.

Biuret test

After adding potassium hydroxide and copper sulphate no colour developed indicating a negative result.

Conclusion

The unknown substance is a protein containing both reducing and non-reducing sugars.

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