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Question 37 — Forensic Chemistry (25 marks) Answer parts (a)–(c) in Section II Answer Booklet 1 - HSC - SSCE Chemistry - Question 37 - 2011 - Paper 1
Question 37
Question 37 — Forensic Chemistry (25 marks) Answer parts (a)–(c) in Section II Answer Booklet 1. (a) Identify the structure shown, and justify your answer. (b) (i... show full transcript
Worked Solution & Example Answer:Question 37 — Forensic Chemistry (25 marks) Answer parts (a)–(c) in Section II Answer Booklet 1 - HSC - SSCE Chemistry - Question 37 - 2011 - Paper 1
Step 1
Identify the structure shown, and justify your answer.
Answer
The structure displayed consists of two monosaccharide units, each exhibiting hydroxyl (-OH) groups and a free carbonyl group. This corresponds to a disaccharide.
To justify this answer:
- Naming the Structure: The structure is identified as sucrose, a common disaccharide formed from glucose and fructose.
- Identifying the Free Carbonyl Group: The free carbonyl group is located at the C1 position of glucose and C2 position of fructose.
- Oxidation/Reducing Sugar: Sucrose is classified as a non-reducing sugar because the glycosidic bond formed between glucose and fructose prevents oxidation.
Step 2
Using the general formula of an amino acid, write an equation to show the formation of a dipeptide.
Answer
The general formula for an amino acid is
To illustrate the formation of a dipeptide, consider two amino acids: Glycine (Gly) and Alanine (Ala). The equation of their reaction can be written as:
Here, the amino group of one amino acid reacts with the carboxyl group of another, releasing a molecule of water and forming a peptide bond.
Step 3
Explain the principles of paper chromatography, with reference to the separation of amino acids.
Answer
Paper chromatography is a technique used to separate mixtures of substances based on their differing affinities to the stationary phase (the paper) and the mobile phase (the solvent).
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Principle of Separation: When a solution containing amino acids is applied to a chromatography paper and a solvent is allowed to travel through it, the amino acids move at different rates depending on their solubility in the solvent and their affinity for the paper.
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Visualization: This separation can be visualized using ninhydrin, which reacts with amino acids to produce colored spots. Each spot corresponds to a specific amino acid based on its unique Rf value, allowing for identification and analysis.