Class 12 chemistry PYQ solution chapter

 

Q2:The plot of osmotic pressure (П) vs concentration  (molL⁻¹) for a solution gives a straight line with slope  25.73L bar mol⁻¹. The temperature at which the osmotic pressure measurement is done is
(Use R = 0.083 L bar mol^-1 K^-1)    (NEET 2024)    

(a) 37^∘C
(b) 310^∘C
(c) 25.73^∘C
(d) 12.05^∘C

Ans: (a)
                            

                                                      Explanation video in tamil language

The relationship between the osmotic pressure (Π) of a solution and its concentration (c) can be derived from the van't Hoff equation for dilute solutions, which is given by:
Π = cRT
where:
Π  is the osmotic pressure,
c is the concentration of the solution in moles per liter,

R  is the ideal gas constant in appropriate units, and
T  is the temperature in Kelvin.
According to the problem, the slope of the Π vs c plot is given as    25.73L bar mol⁻¹ which corresponds to the product RT from the van't Hoff equation. We are provided with the value of the gas constant    
R = 0.083 L bar mol⁻¹ K⁻¹.
To find the temperature
T, we use the following equation derived from the slope of the line:
RT=25.73 L bar mol⁻¹
To isolate T, we rearrange the equation:

T=25.73 L bar mol⁻¹ / 0.083 L bar mol⁻¹ K⁻¹ ≈ 310 K

To convert this temperature from Kelvin to Celsius, we use the conversion formula:

This value is closest to 37^∘C, which corresponds to Option A. Therefore, the temperature at which the osmotic pressure measurement is done is approximately 37^∘C.