Proteins

Discover proteins in a solution with the use of copper sulfate!

Difficulty:
Danger:
Duration:
10 minutes
Experiment's video preview

Reagents

Safety

  • Put on protective gloves and eyewear.
  • Conduct the experiment on the plastic tray.
General safety rules
  • Do not allow chemicals to come into contact with the eyes or mouth.
  • Keep young children, animals and those not wearing eye protection away from the experimental area.
  • Store this experimental set out of reach of children under 12 years of age.
  • Clean all equipment after use.
  • Make sure that all containers are fully closed and properly stored after use.
  • Ensure that all empty containers are disposed of properly.
  • Do not use any equipment which has not been supplied with the set or recommended in the instructions for use.
  • Do not replace foodstuffs in original container. Dispose of immediately.
General first aid information
  • In case of eye contact: Wash out eye with plenty of water, holding eye open if necessary. Seek immediate medical advice.
  • If swallowed: Wash out mouth with water, drink some fresh water. Do not induce vomiting. Seek immediate medical advice.
  • In case of inhalation: Remove person to fresh air.
  • In case of skin contact and burns: Wash affected area with plenty of water for at least 10 minutes.
  • In case of doubt, seek medical advice without delay. Take the chemical and its container with you.
  • In case of injury always seek medical advice.
Advice for supervising adults
  • The incorrect use of chemicals can cause injury and damage to health. Only carry out those experiments which are listed in the instructions.
  • This experimental set is for use only by children over 12 years.
  • Because children’s abilities vary so much, even within age groups, supervising adults should exercise discretion as to which experiments are suitable and safe for them. The instructions should enable supervisors to assess any experiment to establish its suitability for a particular child.
  • The supervising adult should discuss the warnings and safety information with the child or children before commencing the experiments. Particular attention should be paid to the safe handling of acids, alkalis and flammable liquids.
  • The area surrounding the experiment should be kept clear of any obstructions and away from the storage of food. It should be well lit and ventilated and close to a water supply. A solid table with a heat resistant top should be provided
  • Substances in non-reclosable packaging should be used up (completely) during the course of one experiment, i.e. after opening the package.

FAQ and troubleshooting

In what other products can we find protein?

If you used egg white for this experiment then you can also try it with the yolk. The reaction also goes through with milk!

Step-by-step instructions

  1. Crack 1 raw chicken egg into a plate.
  2. Gather 0.5ml of egg white or yolk into the pipette.
  3. Pour the contents of the pipette into the tube "1". 4.Fill the vials #1 and #2 halfway with water. The vial #2 will be served as a reference.
  4. Add 2 drops of 0.4M CuSO4 solution into each vial.
  5. Add 10 drops of 2M Na2CO3 solution into each vial.
  6. Close both vials securely and shake them.
  7. Compare the color of resulting solutions.
  8. To repeat this experiment, make sure to thoroughly wash the vials.
Graphical step-by-step instruction

Disposal

Dispose of solid waste together with household garbage. Pour solutions down the sink. Wash with an excess of water.

Scientific description

Why does the solution with protein turn violet?

A complex compound of copper ions and protein forms in the solution. This compound gives such coloring.

Learn more

The reaction between copper ions and proteins is also called biuret. It is so sensitive, that with the help of this reaction it is possible to find proteins in lots of products.

How does the complex of protein and copper ions form?

Let’s imagine proteins as very long chains, twisted into several spirals, which contain many different segments: small, big, round and rectangular, and so on. These segments are amino acids – organic compounds with carboxyl (–COOH) and amino (–NH2) groups. While in an ordinary chain, segments are simply linked one after another, in proteins amino acids bind to each other with the help of special peptide bonds. Such bonds form when a carboxyl group of one amino acid reacts with an amino group of another acid (as a result, such bonds always involve a nitrogen atom). Copper ions readily react with nitrogen atoms from peptide bonds. This is how a complex with the characteristic violet color is formed.

Why do we add sodium carbonate?

To form a complex of copper ions and protein, a basic medium is required. Sodium carbonate is used to create a basic medium in the experiment.