Advertisements
Advertisements
Question
What is meant by positive deviations from Raoult's law? Give an example. What is the sign of ∆mixH for positive deviation?
Advertisements
Solution
The solutions that do not obey Raoult’s law over the entire range of concentration are known as non-ideal solutions. They have vapour pressures either higher or lower than those predicted by Raoult’s law. If the vapour pressure is higher, then the solution is said to exhibit a positive deviation from Raoult’s law.
A mixture of ethanol and acetone is an example of a solution that shows a positive deviation from Raoult’s law.
In case of solutions showing positive deviations, absorption of heat takes place; that is, ΔmixH has a positive sign.
APPEARS IN
RELATED QUESTIONS
What type of deviation is shown by a mixture of ethanol and acetone? Give reason.
The vapour pressures of pure liquids A and B are 450 and 700 mm Hg respectively, at 350 K. Find out the composition of the liquid mixture if the total vapour pressure is 600 mm Hg. Also, find the composition of the vapour phase.
An aqueous solution of 2% non-volatile solute exerts a pressure of 1.004 bar at the normal boiling point of the solvent. What is the molar mass of the solute?
A solution containing 30 g of non-volatile solute exactly in 90 g of water has a vapour pressure of 2.8 kPa at 298 K. Further, 18 g of water is then added to the solution and the new vapour pressure becomes 2.9 kPa at 298 K. Calculate:
- molar mass of the solute.
- vapour pressure of water at 298 K.
Benzene and toluene form ideal solution over the entire range of composition. The vapour pressure of pure benzene and toluene at 300 K are 50.71 mm Hg and 32.06 mm Hg respectively. Calculate the mole fraction of benzene in vapour phase if 80 g of benzene is mixed with 100 g of toluene.
What type of azeotrope is formed by positive deviation from Raoult’s law?
What is meant by negative deviation from Raoult's law? Give an example. What is the sign of ∆mixH for negative deviation?
Some liquids on mixing form 'azeotropes'. What are 'azeotropes'?
At equilibrium the rate of dissolution of a solid solute in a volatile liquid solvent is ______.
An azeotropic mixture of two liquids will have a boiling point lower than either of the two liquids when it ______.
