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B.Sc Biochemistry Ideal Solutions — practice questions

Explore 6 free Ideal Solutions questions in B.Sc Biochemistry Chemistry. Open each question or exercise to read its content, reference answers and available explanation.

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Ideal Solutions questions and exercises with answers

Showing questions 1–6 of 6.

The mole fraction of urea ($M = 60\,\text{g/mol}$) in an aqueous solution containing $6\,\text{g}$ of urea in $180\,\text{g}$ of water is approximately:Read the answer and worked solution →For an ideal solution containing two volatile liquids A and B, Raoult's law gives the total vapour pressure as:Read the answer and worked solution →Osmotic pressure of a dilute solution is expressed by van't Hoff's equation as:Read the answer and worked solution →Two solutions are said to be **isotonic** if they:Read the answer and worked solution →If $\mathrm{NaCl}$ undergoes complete dissociation in water, the van't Hoff factor $i$ is:Read the answer and worked solution →Desalination of sea water is best carried out by:Read the answer and worked solution →

Worked practice questions

The mole fraction of urea ($M = 60\,\text{g/mol}$) in an aqueous solution containing $6\,\text{g}$ of urea in $180\,\text{g}$ of water is approximately:

  1. $0.010$
  2. $0.005$
  3. $0.100$
  4. $0.050$
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Correct answer: A. $0.010$

Moles of urea $= 6/60 = 0.10$. Moles of water $= 180/18 = 10.0$. Mole fraction of urea $= 0.10/(0.10 + 10.0) = 0.10/10.10 \approx 0.0099 \approx 0.010$.

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For an ideal solution containing two volatile liquids A and B, Raoult's law gives the total vapour pressure as:

  1. $p_T = p_A^\circ p_B^\circ$
  2. $p_T = p_A^\circ \chi_B + p_B^\circ \chi_A$
  3. $p_T = p_A^\circ + p_B^\circ$
  4. $p_T = p_A^\circ \chi_A + p_B^\circ \chi_B$
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Correct answer: D. $p_T = p_A^\circ \chi_A + p_B^\circ \chi_B$

**Raoult's law for an ideal solution:** each component's partial pressure equals its mole fraction in the solution times the vapour pressure of the pure component, $p_i = p_i^\circ \chi_i$. By Dalton's law the total is $p_T = p_A^\circ \chi_A + p_B^\circ \chi_B$.

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Osmotic pressure of a dilute solution is expressed by van't Hoff's equation as:

  1. $\pi = CRT$
  2. $\pi V = nR$
  3. $\pi = nRT$
  4. $\pi = RT/C$
Show answer and solution

Correct answer: A. $\pi = CRT$

For a dilute solution behaving ideally, $\pi = C R T$, where $C$ is the molar concentration of solute, $R$ the gas constant and $T$ the absolute temperature. Equivalently $\pi V = n R T$, structurally identical to the ideal-gas equation with osmotic pressure playing the role of $p$.

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