Display in Beakers :

Display in Test tube : A protein (Egg white), B Glucose solution 1%, C oil, D Starch solution 1%, E Distilled water.

The solution you need to use for this is called Biurets solution.

In some schools, this will be given to you as one solution, which is copper sulphate blue in colour, but in most you will be given two solutions to mix together.

• The first step is to add equal volumes (dropwise) of 1% copper sulphate (sometimes called Biurets A) and either 1% potassium hydroxide or sodium hydroxide (Biurets B) to a test tube.

• After adding Biurets A and B, you'll have a lump of blue precipitate at the bottom of the test tube.

• Hand-warm the precipitate until it becomes liquid (you can do this in a water bath set at 40).

• The easiest test to do to see the positive result is to test egg white or milk. Add some of the egg white to the Biurets solution in the test tube and mix thoroughly while still hand warming. The blue colour will change to violet if protein is present. If protein is not present, the blue colour will remain.

Sometime Stopclock to time out heating benedict for Sugar

Reagents for experiments on ‘Food tests’ and ‘Enzymes’

Unless otherwise stated, 'water' means tap-water.

I% starch solution. 1 g soluble starch powder per 100 cm3 water. Shake the powder in a portion of the water (about 10 cm3) and heat to boiling point to obtain a clear solution. Add the rest of the water.

The solution will keep for several days but all the instructions in this series are based on the assumption that the solution is freshly prepared, i.e. not more than 24 hours before use. This is especially important with experiments involving tests for reducing sugars.

The starch from some sources is very readily hydrolysed and may give an ambiguous result when tested with Benedict’s solution. It is a good idea to check for this before embarking on the experiments involving starch solution.

10% glucose. Simply dissolve 10 g glucose per 100 cm3 water. The solution will keep for weeks if not contaminated with fungi.

I% albumen. The properties of egg-white from fresh eggs seem to depend on the age of the eggs and other variables. It is recommended, therefore, that albumen solution or suspension is made from commercially prepared albumen powder. The albumen is dissolved in cold distilled water (This may take several minutes). Store in a refrigerator or make up the solution fresh each time. Do not stir or shake vigorously in preparation because this denatures the protein.

Iodine solution. To make 100 cm3 stock solution, grind I g iodine and 1 g potassium iodide in a mortar while adding distilled water. Pour the solution into a measuring cylinder and dilute to 100 cm3. Do not store in polythene bottles because the solution will become decolourized.

For experiments with enzymes, dilute 5 cm3 of the stock solution with l00 cm3 water. The

diluted iodine does not keep well.

Benedict's solution. To make 1 litre, dissolve 170 g sodium citrate crystals and 100 g sodium carbonate crystals in 800 cm3 warm distilled water. Dissolve separately 17.0 g copper(II) sulphate(VI) crystals in 200 cm3 cold distilled water. Add the copper sulphate solution to the first solution with constant stirring.

Biuret test. Bench sodium hydroxide solution (2M or 10%) is satisfactory though the reaction will occur with more dilute solutions ( e.g. 0.1 %). The dilute copper(II) sulphate(VI) is a 1% solution in distilled water.

0.05M sodium carbonate solution Dissolve 5.3 g of the anhydrous salt in 1 litre of distilled water

0.1M ethanoic (acetic) acid Place 6 cm3 glacial ethanoic acid in a graduated flask and make up the volume to 1 litre with distilled water.

Alcohol (for dissolving fats). Propan-2-ol [isopropanol] is preferred.

0.1M hydrochloric acid. Dilute 10 cm3 conc. HCl with 990 cm3 water.

Bench hydrochloric acid (2M). Dilute 100 cm3 conc. HCl with 400 cm3 water.