AQA Specimen Paper 3 Q3

Answers available below

. 1 0 3 A peptide is hydrolysed to form a solution containing a mixture of amino acids. This mixture is then analysed by silica gel thin-layer chromatography (TLC) using a toxic solvent. The individual amino acids are identified from their Rf values. Part of the practical procedure is given below. 1. Wearing plastic gloves to hold a TLC plate, draw a pencil line 1.5 cm from the bottom of the plate. Use a capillary tube to apply a very small drop of the solution of amino acids to the mid-point of the pencil line. Allow the spot to dry completely. In the developing tank, add the developing solvent to a depth of not more than 1 cm. Place your TLC plate in the developing tank. Allow the developing solvent to rise up the plate to the top. Remove the plate and quickly mark the position of the solvent front with a pencil. Allow the plate to dry in a fume cupboard. 2. 3. 4. 5. 6. 7. 8. Parts of the procedure are in bold text. For each of these parts, consider whether it is essential and justify your answer. [4 marks] Barcode Typesetter code<br /> . 2 0 3 Outline the steps needed to locate the positions of the amino acids on the TLC plate and to determine their Rf values. Barcode 0 3 . 3 Explain why different amino acids have different Rf values. [4 marks] [2 marks] Typesetter code Turn over <br />

Show answer