Neco Model Questions Vol1 2025 Biology Question 3

A student is required to determine the percentage of carbohydrate (starch) in a 2.00 g sample of a commercial biscuit using the iodine colour‑intensity method. The procedure is as follows: 1. Weigh 2.00 g of biscuit and grind to a fine powder. 2. Add 100 mL of distilled water, stir for 5 min and filter to obtain a clear extract. 3. Prepare four standard starch solutions of known concentration: 0.5 % (w/v), 1.0 % (w/v), 1.5 % (w/v) and 2.0 % (w/v). Add a few drops of iodine solution to each and record the colour intensity on a scale of 1 (very pale) to 5 (deep blue). 4. Add iodine to the biscuit extract and record its colour intensity. The colour‑intensity observations are shown in the table below. | Solution | Starch concentration (% w/v) | Colour intensity (1–5) | |---------------------|------------------------------|------------------------| | Standard 1 | 0.5 | 2 | | Standard 2 | 1.0 | 3 | | Standard 3 | 1.5 | 4 | | Standard 4 | 2.0 | 5 | | Biscuit extract | – | 3.6 | Using the data above, answer the following: