Investigation to determine the lowest concentration of copper (II) sulphate solution that brings full denaturation of egg albumen.

Practical Examination

Biology - Planning Exercise – April 2003

Introduction

The aim of this investigation is to find the lowest concentration of Copper (II) sulphate needed to give full denaturation to egg albumen. This will be done by adding different concentrations of copper (II) sulphate to a set amount of egg albumen. Egg albumen is found in eggs and is also known as egg white, egg albumen is a type of protein. Proteins are macromolecules made up of chains of amino acids, all the bonds in a protein are covalent. Once the copper (II) sulphate solution is added to the egg albumen it causes it to denature, this can be seen by the coagulation that takes place. This is when the egg albumen changes from a cloudy liquid to a more solid, white state. The denaturation that takes place has the same resulting physical affects on the egg albumen as it would have if it were to be heated e.g. cooking an egg. The reason for egg albumen denaturing is due to the copper ions in the copper (II) sulphate forming strong bonds with carboxylate anions on the amino acids. They form a new set of ionic bonds hence disrupting the peptide bonds and altering the shape and composition of the original protein causing the change to a more solid white state. The positive copper ions also affect the proteins’ electrical polarity, therefore making it insoluble, causing it to precipitate out of solutions. This will be seen later in the experiment once the combined solution of egg albumen and copper (II) sulphate is centrifuged.

I predict that as the concentration of copper (II) sulphate increases, the amount of denaturation will also increase to a point at which 100% denaturation will take place. It is at this point that the lowest concentration necessary for full denaturation is found. I have come to this prediction because it is what I found to occur in the preliminary testing.

ss 100% denaturation

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ss 100% denaturation

Key Variables

Amount of egg albumen used: I decided that I would be using 1cm3 of egg albumen. I made this decision by using different amounts in my preliminary testing and found that this was a suitable amount to denature in this experiment in relation to the amount of copper (II) sulphate that I will use.
Concentration of the copper (II) sulphate: this is determined by the amount of copper (II) sulphate used in relation to the amount of water it is diluted in.
Length of time test tubes are centrifuged for will be 10 minutes: this was also decided through preliminary testing as a suitable amount of time in order for the denatured egg albumen to descend to the bottom of the test tube.
The same centrifuge should be used throughout the experiment therefore making sure that the speed at which the test tubes are centrifuged remain unchanged.
The same weighing scales should also be used throughout the experiment to ensure consistency and allow less room for errors.

Method

In order to obtain accurate and precise results follow the step-by-step method below.

To begin with collect 6 test tubes that are suitable to fit into the centrifuge.
Label each test tube through from A to F. Place the test tubes into a test tube rack in alphabetical order.
Weigh each test tube using the electronic scales, and record the weights in the table provided.
Extract the egg white from one egg and place it into a beaker.
Then syringe 1cm3 of the egg white into each test tube, using a 1cm3 syringe.
Weigh all the test tubes again and record the results.
Add 1cm3 of distilled water into test tube B using a 5cm3 syringe.
Add 2cm3 of distilled water into test tube C using a 5cm3 syringe.
Add 3cm3 of distilled water into test tube D using a 5cm3 syringe.
Add 4cm3 of distilled water into test tube E using a 5cm3 syringe.
Add 5cm3 of distilled water into test tube F using a 5cm3 syringe.
Add 5cm3 of copper (II) sulphate solution into test tube A using a different 5cm3 syringe.
Add 4cm3 of copper (II) sulphate solution into test tube B using a 5cm3 syringe.
Add 3cm3 of copper (II) sulphate solution into test tube C using a 5cm3 syringe.
Add 2cm3 of copper (II) sulphate solution into test tube D using a 5cm3 syringe.
Add 1cm3 of copper (II) sulphate solution into test tube E using a 5cm3 syringe.
Place all the test tubes into the centrifuge.
Turn on the centrifuge for 10 minutes, timing using a stop clock.
After 10 minutes all of the coagulated egg albumen will have settled at the bottom of the test tubes.
Pour out the copper sulphate solution, which will be found on top of the coagulated egg albumen.
Weigh the test tubes again, and record the results.

The table on page 3 illustrates steps 7 through to 16 showing the correct amounts of egg albumen, distilled water and 0.1mol dm-3 copper (II) sulphate solution needed to conduct the experiment.

The reason for adding water is to dilute the copper (II) sulphate solution. Test tube A has the solution at full concentration this concentration is decreased in test tubes A through to F as more and more water is added.

Apparatus

1 Egg
1 Beaker
A supply of 0.1mol dm-3 copper (II) sulphate solution
Centrifuge
6 Test tubes
1 Test tube rack
2-5cm3 Syringes
1-1cm3 Syringe
Distilled water
Electronic scales
Stop clock

Results

The results from the experiment should all be recorded in the table provided. The first column shows the label each test tube should have. The second column should record the initial weight of the empty test tubes, the reason for this being that in my pre-testing I found that not all the test tubes had the same weight. The third column should record the weight of the test tube with 1cm3 of egg albumen. The forth column should be filled with the weight of the test tube after steps 17 to 20 in the method. The weight of the denatured egg albumen is to be recorded on the final column, in order to work this out subtract the contents of the forth column from the third column, then subtract your answer from the second column giving you the weight of denatured egg albumen. All weight should be recorded in grams and with two decimal places.

Justification

I carried out various types of preliminary testing before deciding on the final method by which the experiment is to be carried out. This included the possibility of using a colorimeter to test the absorbance of light in relation to the copper (II) sulphate concentration for full denaturation of the egg albumen. I also tried a method of filtering the egg albumen and copper (II) sulphate solution using filter paper to remove the product, which was the denatured egg albumen. This method could have been used to replace the centrifuge. However I decided not to use this method, as it was not as accurate and left a higher margin for error. The equipment I chose to use is the most available and accurate for the task. Both 1cm3 and 5cm3 syringes are needed because when measuring smaller volumes they are more accurate. In my preliminary testing I also found that not all test tubes had the same weight therefore they would all have to be weighed before adding the solutions and subsequently their weights would have to be subtracted from the final results.

Safety

In order to ensure that the experiment is carried out safely handle all equipment with care. When using the centrifuge make sure you are shown how to use it from a member of staff.

Preliminary results

My preliminary results show that the concentration used in test tube C gives the lowest concentration of copper (II) sulphate solution that brings full denaturation of the egg albumen. In this case the concentration of copper (II) sulphate used was 0.06mol dm-3.

References