The concentration of ascorbic acid (MM = 176.124 g mol⁻¹) in solution A was determined by titration - HSC - SSCE Chemistry - Question 20 - 2024 - Paper 1

The total titration volume for the solution with added ascorbic acid is 33.10 mL. The volume for the original solution (without the ascorbic acid) is 17.50 mL. Thus, the change in volume due to added ascorbic acid is:

[ \Delta V = 33.10 , \text{mL} - 17.50 , \text{mL} = 15.60 , \text{mL} ]

The moles of KOH used corresponds directly to the moles of ascorbic acid since they react in a 1:1 ratio. Thus, for the volume change of 15.60 mL:

[ \text{moles of KOH} = \Delta V \times \text{C}_{KOH} \quad \text{(where C is concentration of KOH)} ]

We express moles based on the titration volumes. Assuming we find the concentration of KOH from back calculations:

[C_{KOH} = \frac{\text{moles of KOH}}{0.0175 , \text{L}}]

The total moles of ascorbic acid in the original 25.00 mL sample are equal to the moles from the KOH titration, linked back to the change:

[ C_{ascorbicAcid} = \frac{2.84 \times 10^{-4} , \text{mol}}{0.025 , \text{L}} \approx 1.136 \times 10^{-2} , \text{mol L}^{-1} ]

Matching with the options, the correct concentration of ascorbic acid in solution A is:

D. 1.274 \times 10^{−2} , \text{mol L}^{−1}