Solutions A and B are separated by a semipermeable membrane. Solution A contains $1 \mathrm{mM}$ sucrose and $1 \mathrm{mM}$ urea. Solution B contains $1 \mathrm{mM}$ sucrose. The reflection coefficient for sucrose is one, and the reflection coefficient for urea is zero. Which of the following statements about these solutions is correct?

Question

Quizplus · Accepted Answer

[III A, B 4]. Solution A contains both sucrose and urea at concentrations of $1 \mathrm{mM}$, whereas solution $B$ contains only sucrose at a concentration of $1 \mathrm{mM}$. The calculated osmolarity of solution A is $2 \mathrm{mOsm} / \mathrm{L}$, and the calculated osmolarity of solution B is $1 \mathrm{mOsm} / \mathrm{L}$. Therefore, solution A, which has a higher osmolarity, is hyperosmotic
with respect to solution B. Actually, solutions A and B have the same effective osmotic pressure (i.e., they are isotonic) because the only "effective" solute is sucrose, which has the same concentration in both solutions. Urea is not an effective solute because its reflection coefficient is zero.

Solutions a and B Are Separated by a Semipermeable Membrane 1mM1 \mathrm{mM}1mM

Solutions a and B Are Separated by a Semipermeable Membrane $1 \mathrm{mM}$