Answer the following: Calculate the mass of ascorbic acid (molecular mass ) to be dissolved in of…
Answer the following:
(i)[2.0]
Calculate the mass of ascorbic acid (molecular mass $= 176\text{ g mol}^{-1}$) to be dissolved in $75\text{ g}$ of acetic acid to lower its freezing point by $1\cdot5^\circ\text{C}$. Assume that the solute neither associates nor dissociates in solution.
($K_f$ for acetic acid $= 3\cdot9\text{ K kg mol}^{-1}$)
(ii)[2.0]
A solution of an organic compound was prepared by dissolving $6\cdot8\text{ g}$ in $0\cdot1\text{ litre}$ of water. Calculate the osmotic pressure of this solution at $25^\circ\text{C}$.
(Molecular mass of organic compound $= 321\cdot45\text{ g mol}^{-1}$)
(iii)[1.0]
Why are aquatic species more comfortable in cold water than warm water?
Answer
Answer (i)
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Formula:
$\Delta T_f = \frac{K_f \times w_2 \times 1000}{M_2 \times w_1}$
$w_2 = \frac{\Delta T_f \times M_2 \times w_1}{K_f \times 1000}$
Substitution:
$w_2 = \frac{1\cdot5\text{ K} \times 176\text{ g mol}^{-1} \times 75\text{ g}}{3\cdot9\text{ K kg mol}^{-1} \times 1000\text{ g kg}^{-1}}$
$= \frac{19,800}{3900} = 5\cdot08\text{ g}$
Final answer: 5.08 g
Final answer: 5.08 g
Answer (ii)
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Formula:
$\Pi = \frac{w \times R \times T}{M \times V}$
Substitution:
$w = 6\cdot8\text{ g}$
$V = 0\cdot1\text{ L}$
$T = 25 + 273 = 298\text{ K}$
$M = 321\cdot45\text{ g mol}^{-1}$
$R = 0\cdot0821\text{ L atm K}^{-1}\text{mol}^{-1}$
$\Pi = \frac{6\cdot8\text{ g} \times 0\cdot0821\text{ L atm K}^{-1}\text{mol}^{-1} \times 298\text{ K}}{321\cdot45\text{ g mol}^{-1} \times 0\cdot1\text{ L}}$
$= \frac{166\cdot37}{32\cdot145} = 5\cdot18\text{ atm}$
Final answer: 5.18 atm
Final answer: 5.18 atm
Answer (iii)
AIWritten by AI (gemini) - it can contain mistakes.
According to Henry's law, the solubility of a gas in a liquid decreases with an increase in temperature because gas dissolution is an exothermic process. Therefore, cold water has a higher concentration of dissolved oxygen than warm water, which allows aquatic species to breathe more easily.
From ISC 2026 Chemistry Paper 1, question 19.