Question

20 g of a substance were dissolved in 500 mL of water and the osmotic pressure of the solution was found to be 600 mm of mercury at 15°C. The molecular weight of the substance is ______.

पर्याय

• 998

• 1028

• 1098

• 1198

Answer 1

20 g of a substance were dissolved in 500 mL of water and the osmotic pressure of the solution was found to be 600 mm of mercury at 15°C. The molecular weight of the substance is 1198.

Explanation:

To find the molecular weight (M), we use the van't Hoff equation for osmotic pressure:

`pi = (wRT)/(MV)`

Convert Given Units to Standard Form:

Mass (w) = 20 g

Volume (V) = 500 mL = 0.5 L

Osmotic Pressure (π) = `(600  "mm Hg")/(760  "mm Hg/atm")` ≈ 0.7895 atm

Temperature (T) = 15°C + 273.15 = 288.15 K

Gas Constant (R) = 0.0821 L · atm · K⁻¹ · mol⁻¹

Rearranging the formula gives:

`M = (wRT)/(piV)`

`M = (20 xx 0.0821 xx 288.15)/(0.7895 xx 0.5)`

`M ≈ 1198.6` g/mol