Calculate the mass of ascorbic acid


Calculate the mass of ascorbic acid (Vitamin C, C6H8O6) to be dissolved in 75 g of acetic acid to lower its melting point by 1.5°C. Kf = 3.9 K kg mol−1.


Mass of acetic acid, w1 = 75 g

Molar mass of ascorbic acid (C6H8O6), M2 = 6 × 12 + 8 × 1 + 6 × 16

= 176 g mol−1

Lowering of melting point, ΔTf = 1.5 K

We know that:

$\Delta T_{f}=\frac{K_{f} \times w_{2} \times 1000}{M_{2} \times w_{1}}$

$\Rightarrow w_{2}=\frac{\Delta T_{f} \times M_{2} \times w_{1}}{K_{f} \times 1000}$

$=\frac{1.5 \times 176 \times 75}{3.9 \times 1000}$

= 5.08 g (approx)

Hence, 5.08 g of ascorbic acid is needed to be dissolved.


Note: There is a slight variation in this answer and the one given in the NCERT textbook.

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Kieran Oakes
Feb. 14, 2023, 3:37 p.m.
Hi administrator, Your posts are always insightful and valuable.
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