The vapour pressure of water is 12.3 kPa at 300 K. Calculate vapour pressure of 1 molal solution of a non-volatile solute in it.
Answers
What is vapour pressure ?: Vapor pressure also known as equilibrium vapor pressure is defined as the pressure exerted by a vapor in the state of thermodynamic equilibrium with its condensed phases that may be solid or liquid, at a given temperature in an enclosed system. .
What is 1 molal solution? :
A molality is defined as the number of moles of solute dissolved in one kilogram of solvent.
Therefore, the formula weight for NaCl is 58, and 58 grams of NaCl dissolved in 1kg water would result in a 1 molal solution of NaCl. 1 molal solution means 1 mol of the solute is present in 1000 g of the solvent (water).Molar mass of water = 18 g mol - 1∴
Number of moles present in 1000 g of water = 1000/18= 55.56 molTherefore, mole fraction of the solute in the solution isx2 = 1 / (1+55.56) = 0.0177.
It is given that,Vapour pressure of water, p10 = 12.3 kPa.
Applying the relation, (P10 - P1) / P10 = X2 ⇒ (12.3 - p1) / 12.3 =0.0177⇒ 12.3 - P1 = 0.2177⇒ p1 = 12.0823ie.
p1 = vapour pressure of 1 molal solution of a non-volatile solute= 12.08 kPa (approximately)
Hence, the vapour pressure of the solution is 12.08 kPa.
hope you got ur answer.......
