Neco Model Questions Vol1 2017 Biology Question 3

A student is investigating the carbohydrate content of a 5.00 g sample of boiled rice using the Benedict’s test. The procedure is as follows: 1. Prepare standard glucose solutions of known concentrations (0, 2, 4 and 6 mg ml⁻¹) and add 2 ml of each to separate test tubes. 2. Add 2 ml of Benedict’s reagent to each tube, heat in a boiling water bath for 5 min and cool. 3. Measure the absorbance of each coloured solution at 540 nm using a colour‑meter. The recorded absorbances are: - 0 mg ml⁻¹ : 0.000 - 2 mg ml⁻¹ : 0.210 - 4 mg ml⁻¹ : 0.415 - 6 mg ml⁻¹ : 0.620 4. Prepare an extract of the rice sample by boiling 5.00 g of the rice in 50 ml of distilled water, filtering and taking 2 ml of the filtrate for the test. The absorbance of the rice extract after adding Benedict’s reagent and heating is 0.425. Answer the following questions: