Question

Solution A contains 100 mM CaCl₂ and 50 mM glucose. Solution B contains 175 mM NaCl. These solutions are seperated by a membrane that is permeable to all solutes except glucose. Which of the following best describes solution A in comparison to solution B?

A. Isosmotic; Hypertonic.
B. Isosmotic; Isotonic.
C. Hyposmotic; Isotonic.
D. Hyperosmotic; Isotonic.
E. Hyposmotic; Hypotonic.

Answer 1

Solution A is isosmotic to Solution B, but hypertonic because of the additional osmotic pressure exerted by the non-permeating glucose. Isosmotic refers to the equal osmolarity due to ions that can cross the membrane, while hypertonicity is due to the non-permeating solute, glucose, in Solution A.

Step-by-step explanation:

The correct answer to the given question is A. Isosmotic; Hypertonic. Since the membrane is permeable to all solutes except glucose, we only consider the ions that can cross the membrane for our comparison between solution A and solution B. Solution A has 100 mM CaCl₂, which would dissociate into 100 mM Ca²⁺ and 200 mM Cl⁻, because each unit of CaCl₂ yields one calcium ion and two chloride ions. So, the total concentration of permeable solute particles in solution A is 300 mM. Solution B has 175 mM NaCl, which would dissociate into 175 mM Na⁺ and 175 mM Cl⁻, making the total concentration 350 mM.

Though the total solute concentrations differ, when taking into account only the permeable solutes, the solutions are isosmotic because they have the same overall number of solute particles per unit volume. However, since solution A has glucose, which cannot cross the membrane, it will exert additional osmotic pressure, making solution A hypertonic relative to solution B.