Question

The osmotic pressure of a decimolar solution of urea at $27^\circ C$ is
A. $2.49bar$
B. $5bar$
C. $3.4bar$
D. $1.25bar$

Answer 1

Generally, decimolar word is simply implying decimal which means in fraction denominator will be 10.
In this question, we have to calculate the osmotic pressure of a decimolar solution (Concentration of solution is $\dfrac{1}{{10}}M$ or $0.1M$) at a particular temperature .

Complete step by step answer:
Osmotic pressure can be defined as the minimum pressure that must be applied to a solution to halt the flow of solvent molecules through a semipermeable membrane (osmosis).
It is a Colligative property and is dependent on the concentration of solute particles in the solution.
Osmotic pressure can be calculated with the help of the following formula:
$\pi = \,i\,CRT$
Where,
π is the osmotic pressure
i is the van’t hoff factor
C is the molar concentration of the solute in the solution can be also written as $M = \dfrac{n}{V}$
Where, M is Molarity, n is number of moles of solute, V is volume of solution in litre.
R is the universal gas constant and the value is $0.0821$
T is the temperature
According to the question,
Molarity is defined as the number of moles of solute dissolved in 1 litre of solution. Denoted by M and its unit is moles/l.
$\Rightarrow$ Molarity (M)
Given temperature (T) $27^\circ C = 27 + 273 = 300K$
According to Osmotic Pressure,
$\pi = MRT$
Substituting the value of M, R and T in above equation
$= 0.1 \times 0.0821 \times 300$
So, we get $\pi = 2.463atm$
And we know $1atm = 1.01325bar$
So $\pi = 2.463 \times 1.01325 = 2.49bar$

So, the correct answer is Option A.

Note: So , Mainly focus on a decimolar solution . Semi molar solution means that the molarity of the solution is $\dfrac{1}{2}$ . Decimolar solution means that the molarity of the solution is $\dfrac{1}{{10}}$ .
While dealing with temperature make sure you are converting temperature properly.