Ijmb Model Questions Vol1 2024 Biology Question 3

A student is investigating the carbohydrate content of a commercial orange juice using the phenol‑sulfuric acid method. The procedure is as follows: 1. Prepare glucose standard solutions of concentrations 0.20, 0.40, 0.60 and 0.80 g per 100 mL. 2. Add 1 mL of each standard to separate test tubes, add 1 mL of phenol solution and 5 mL of concentrated H₂SO₄, mix and allow colour to develop for 10 min. 3. Measure the absorbance of each tube at 490 nm against a reagent blank. 4. Treat 10 mL of the orange‑juice sample in the same way and record its absorbance. The absorbance readings obtained are: | Glucose concentration (g / 100 mL) | Absorbance (490 nm) | |-----------------------------------|----------------------| | 0.20 | 0.120 | | 0.40 | 0.245 | | 0.60 | 0.365 | | 0.80 | 0.485 | The orange‑juice sample gave an absorbance of 0.312. The density of the juice is 1.05 g mL⁻¹. Using this information, answer the questions below.