Question

Blood is isotonic with
(a). 0.16M NaCl
(b). Conc. NaCl
(c). 30% NaCl
(d). 50% NaCl

Answer 1

Hint: If the two solutions have the same osmotic pressure, they are known as isotonic solutions. Generally, 0.9% of NaCl corresponds to isotonic with normal saline. This will determine whether the solute can cross the cell membrane or not.

Complete step by step solution:
All of us have observed that if raisins are soaked in water for some time, they swell. It is due to the flow of water into the raisins through its skin which acts as a semipermeable membrane (permeable only to the solvent molecules). This phenomenon is also observed when two solutions of different concentrations in the same solvent are separated by a semipermeable membrane. In this case the solvent flows from a solution of lower concentration to a solution of higher concentration. The process continues till the concentrations of the solutions on both sides of the membrane become equal.
The spontaneous flow of the solvent from a solution of lower concentration (or pure solvent) to a solution of higher concentration when the two are separated by a semipermeable membrane is known as osmosis.
Also, if the two solutions have the same osmotic pressure, they are known as isotonic solution. This state allows for free movement of water across the membrane without changing the concentration of solutes on either side. When 9 grams of NaCl dissolved in water, a total volume of one liter (0.0158 M) , is a close approximation to the isotonic solution of NaCl in blood. At this concentration, both sodium and chloride ions pass freely through the plasma membrane.
Therefore, the correct option is (a) 0.16M NaCl as per above discussion.

Note: Also, we should know about the concept of osmotic pressure. It is an excess pressure that must be applied to the solution to just prevent the passage of pure solvent into it when the two are separated by a perfect semipermeable membrane. This is a colligative property and has been widely used to determine the molar masses of macromolecules.