Question

write two examples of ideal solution with positive deviation.

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Answer 1

Answer:

The French chemist Francois Raoult discovered the law that mathematically describes the vapor pressure lowering phenomenon.

According to Raoult's law, the partial vapour pressure of each component in any solution is directly proportional to its mole fraction.

If the vapour pressure is higher then the solution is said to exhibit positive deviation, And if the vapour pressure is lower than the solution then it said to be a negative deviation.

Examples of :

Positive Deviation -

Acetone and Carbon disulphide

Acetone and Benzene

Carbon Tetrachloride and Toluene or Chloroform

Methyl Alcohol and Water

Acetone and Ethanol

Ethanol and Water

2. Negative deviation

Chloroform and Benzene

Chloroform and Diether

Acetone and Aniline

Nitric Acid ( HNO3) and water

Acetic Acid and pyridine

Hydrochloric Acid ( HCl) and water

One way to remember these examples is that :

In the ones, with POSITIVE DEVIATION, the intermolecular attractive forces between solute-solvent molecules are weaker than those between solute-solute and solvent-solvent molecules.

For example, a mixture of ethanol and acetone forms a solution with a positive deviation from Raoult's law. In pure ethanol, molecules are hydrogen-bonded. On adding acetone, its molecules get in between the ethanol molecules and break some of the hydrogen bonds between them. Due to the weakening of interactions, the solution shows a positive deviation from Raoult's law

whereas the ones in which there is a NEGATIVE DEVIATION, the intermolecular attractive forces between solute-solvent molecules are stronger than those between solute-solute and solvent-solvent molecules

For example, a mixture of chloroform and acetone forms a solution with a negative deviation from Raoult's law. This is because chloroform molecule is able to form a hydrogen bond with acetone molecule. This decreases the escaping tendency of molecules for each component and consequently the vapour pressure decreases resulting in negative deviation from Raoult's law.