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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 structures shown are glucose molecules linked together.
- Identify the structure: The structure consists of two glucose molecules illustrated as cyclical forms.
- Justification:
- Each glucose molecule has the molecular formula C₆H₁₂O₆.
- The presence of hydroxyl (–OH) groups indicates that these are alcohols, specifically hexa-hydric, further confirming they are carbohydrates.
- The free carbonyl group at C1 suggests that they can act as reducing sugars.
- These structures may participate in glycosidic linkage, typical for sugars.
Step 2
Using the general formula of an amino acid, write an equation to show the formation of a dipeptide.
Answer
Amino acids share the general formula R-CH(NH₂)-COOH, where R is the side chain specific to each amino acid.
To illustrate the formation of a dipeptide, consider two amino acids:
- Amino Acid 1: R1-CH(NH₂)-COOH
- Amino Acid 2: R2-CH(NH₂)-COOH
The equation for dipeptide formation (condensation reaction) can be written as:
Here, a peptide bond forms between the amino group of one amino acid and the carboxyl group of another, releasing a molecule of water.
Step 3
Explain the principles of paper chromatography, with reference to the separation of amino acids.
Answer
Paper chromatography is a technique used for separating and identifying components in a mixture. The separation of amino acids through this method involves the following principles:
- Stationary Phase: The paper acts as the stationary phase, where amino acids will adhere.
- Mobile Phase: A solvent (mobile phase) is used to carry amino acids up the paper. The choice of solvent affects the rate of movement.
- Capillary Action: When the solvent rises through the paper by capillary action, different amino acids travel at different rates based on their affinity to the paper vs. the solvent.
- Rf Value: The distance traveled by each amino acid relative to the solvent front is measured to calculate the Rf value, allowing for identification.
- Visualization: After chromatography, amino acids can be visualized under ultraviolet light or by using specific reagents to react with amino acids, thus allowing quantification and identification.