Ijmb Model Questions Vol1 2020 Biology Question 3

A group of students carried out a titration to determine the ascorbic acid (vitamin C) content of a freshly squeezed orange juice sample using 2,6‑dichlorophenol‑indophenol (DCPIP) dye. The procedure was as follows: 1. 10.0 mL of the orange juice was mixed with 10 mL of 0.1 M oxalic acid solution (to maintain acidity). 2. The mixture was diluted to a final volume of 50 mL with distilled water. 3. 2.00 mL of the diluted solution was transferred to a conical flask and 2 drops of starch indicator were added. 4. The solution was titrated with 0.010 M DCPIP until the blue‑black colour of the starch‑iodine complex disappeared, indicating the endpoint. 5. The volume of DCPIP required to reach the endpoint was recorded as 12.5 mL. Using the data above, answer the following questions: a. Calculate the concentration of ascorbic acid in the original orange juice (expressed in mg L⁻¹). (Molar mass of ascorbic acid = 176.12 g mol⁻¹) b. The Recommended Dietary Allowance (RDA) for vitamin C for an adult male is 90 mg per day. Determine the percentage of the RDA supplied by 250 mL of this orange juice. c. Discuss two possible sources of systematic error in this titration and suggest one practical way to minimise each error.