Question

Solution A (1.0 M Sucrose) and solution B (1.0 M NaCl) are separated by a dialysis membrane. If the membrane is spontaneously permeable to Sucrose, NaCl, and Water, what is the INITIAL reaction of Sucrose, NaCl, and Water?

Answer 1

Dialysis membrane is selectively permeable membrane which allows one type of solute to pass but prevent the other. In addition to this, the size of the pores is crucial for spontaneous diffusion of solute particles from one side to other. The solution A contain 1 M sucrose while that of B has 1 M NaCl solution separated by a dialysis membrane. The membrane is spontaneously pemeable to sucrose, NaCl and water. Now 1 M NaCl is more hypertonic than 1 M sucrose solution because NaCl dissociate into Na+ and Cl- ions in solution and has more number of solute particles as compared to 1 M sucrose solution which remain undissociated in solution. So, the concentration of NaCl is higher in solution B, while concentration of sucrose and water is higher in solution A. Hence, initially sucrose and water will move from region of their higher concentration to the region of their lower concentration. Water molecules move from the side with greater water concentration (lower solute concentration) to the side with lower concentration (higher solute concentration), i.e from A to B. Similarly, sucrose will also diffuse from its higher concentration to lower concentration, i.e from A to B. But NaCl molecules will diffuse in opposite direction, i.e from B to A as number of NaCl particles is higher in B as compared to A. This diffusion of particles continues till the equilibrium is established. So, initially sucrose and water will diffuse from A to B while NaCl will diffuse from B to A.