A 5% solution of cane sugar (molar mass = 342 g mol-1) is isotonic wit...
Isotonic Solutions and Colligative Properties:
An isotonic solution is a solution that has the same osmotic pressure as another solution. In other words, it is a solution in which the concentration of solute particles is the same as that of another solution. The osmotic pressure of a solution depends on the number of solute particles, rather than their chemical nature. This property is known as a colligative property.
The formula to calculate the osmotic pressure of a solution is:
π = (n/V)RT
Where:
π is the osmotic pressure
n/V is the concentration of solute particles in moles per liter (mol/L)
R is the ideal gas constant (0.0821 L·atm/(mol·K))
T is the temperature in Kelvin (K)
Isotonicity between Cane Sugar and Unknown Solute:
Given that the 5% cane sugar solution is isotonic with a 1% solution of the unknown solute, we can assume that the osmotic pressure of both solutions is the same. Therefore, we can equate the osmotic pressure equations for both solutions:
For the cane sugar solution:
π1 = (n1/V1)RT
For the unknown solute solution:
π2 = (n2/V2)RT
Since the osmotic pressures are the same, we can write:
(n1/V1)RT = (n2/V2)RT
Simplifying, we get:
(n1/V1) = (n2/V2)
Since the molar mass of cane sugar (M1) is given as 342 g/mol, and the concentration of the cane sugar solution is 5%, we can write:
(n1/V1) = (0.05/M1)
Similarly, for the unknown solute, let the molar mass be M2. The concentration of the unknown solute solution is given as 1%, so we can write:
(n2/V2) = (0.01/M2)
Equating these expressions, we have:
(0.05/M1) = (0.01/M2)
Solving for M2, we get:
M2 = (0.01/M1) * (M2/0.05)
M2 = (0.01/0.05) * M1
M2 = 0.2 * M1
Substituting the molar mass of cane sugar (M1 = 342 g/mol), we get:
M2 = 0.2 * 342
M2 = 68.4 g/mol
Therefore, the molar mass of the unknown solute is 68.4 g/mol, which corresponds to option 'C'.