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The Effect of pH on the Strength of Keratin (hair protein).

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Introduction

Science Plan The Effect of pH on the Strength of Keratin (hair protein) Relevant Information: Keratin is a fibrous protein and has a structural function. Fibrous proteins contain polypeptides that bind together to form very long fibres running parallel to each other. These fibres are linked by cross-bridges that make the protein strong and insoluble. The main constituent of hair is the protein keratin. Keratin can also be found in horns, nails, claws and feathers. These examples suggest keratin has a strong structure. Like most other proteins it is made of monomers called amino acids. All Amino acids contain both an acidic carboxylic group (-COOH) and a basic amino group (-NH2); there is also an R group that changes with each different amino acid. They all consist of carbon, hydrogen, oxygen and nitrogen atoms. Keratin also contains a high concentration of the amino acid cysteine; this contains a sulphur atom. The sulphur atoms from two cysteines join together, forming a very strong disulphide bond. These bonds are covalent and form strong links making the tertiary structure of the protein very stable. The disulphide bonds occur down the length of the keratin fibre and the cross-linking between the keratin chains account for the strength of hair. ...read more.

Middle

The five test dishes will be cleaned in pH neutral solution and rinsed with distilled water, this is to prevent contamination. The five pH solutions will have varying values across the pH scale. A strong acid (pH 1-4), a weak acid (pH 4-6.4), a neutral (pH 7), a weak alkali (pH 7.5-9.9) and a strong alkali (pH 10-14) will be used to test individual hairs. This range is representative of the principal pH values. The chemical compounds chosen to represent these pH values are Hydrochloric Acid, Acetic Acid, Water, Calcium Hydroxide and Sodium Hydroxide respectively. These compounds are commonly used in the laboratory and practical to obtain. Also their pH values correspond to the values chosen to test. Each test dish will have a 2cm3 chemical solution with a concentration of 0.5M. This concentrate is the safest amount to use whilst still getting a strong pH. The five separate experiments will be conducted simultaneously so that all the conditions are the same. The dishes and splints must be labelled accordingly with their pH values. The corresponding splint will be placed into the solution, the hair is to be exposed for 10 minutes, to ensure that the hair has been exposed thoroughly. The hair will be removed gently and rinsed with distilled water and allowed to stand to air dry. ...read more.

Conclusion

A laboratory coat is also to be worn. Hair tied up. Keep at a distance from bases. General Use: Wear eye protection and gloves. Used with careful supervision. Acetic Acid- CORROSIVE Causes severe burns; avoid contact with liquid or vapour in the eyes, on the skin, by breathing, or on clothing. Solution to be kept in a cool place and avoid liquid or vapour contact. In the 0.5M solution to be used the chemical is an IRRITANT. General Use: Gloves must be worn and protective eyewear as a precaution. Use bottle carriers for transporting acid bottles. Segregate acids from bases. Calcium Hydroxide- CORROSIVE Inhalation causes irritation to the respiratory tract. Symptoms may include coughing, shortness of breath. Calcium hydroxide is CORROSIVE General Use: Gloves and eyewear must be worn at all times to reduce exposure to hands. Sodium Hydroxide- CORROSIVE Causes severe burns. Very dangerous to eyes and skin. Solution will be equal to 0.5 M and should be labelled CORROSIVE. General Use: Eye protection is very important. The solution must not be handled directly. The use of beakers with handles is safer, as they are less likely to be dropped Ethical Implications: The donor of the hair, must consent to the manner the hair will be used and agree with the testing. The hair should be chosen from a healthy individual who does not suffer from a hair disorder. ...read more.

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A good description of the plan including detailed, relevant background theory. The method could be improved by describing fully how all control variables are to kept constant so that only changes to the independent variable should affect the results.

Marked by teacher Adam Roberts 14/10/2013

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