Passage:

Solubility of gases in liquids is greatly affected by pressure and temperature. Henry gave the quantitative relationship between pressure and solubility of gas in a solvent. According to Henry’s law, partial pressure of a gas above a liquid is directly proportional to its mole fraction in solution and is expressed as \(P = K_H.x\), where \(K_H\) is Henry’s constant and x is mole fraction of gas. \(K_H\) is a function of nature of gas.

F M Raoult gave a quantitative relationship between partial pressures and mole fractions in the binary solution of volatile liquids. Raoult’s law states that for a binary solution of volatile liquids, the partial pressure of each component in the solution is directly proportional to its mole fraction. Thus for a solution of component \(1\) and \(2\), partial pressure of each component\(P_1 = p_1^0x_1\), where \(p_1^0\) is the vapour pressure of pure component \(1\) at the same temperature. Similarly \(P_2 = p_2^0x_2\)

Which of the following show negative deviation from Raoult’s law?

Acetone and Chloroform

The correct answer is option 3. Acetone and Chloroform.

Raoult's law states that the partial vapor pressure of each component in a solution is proportional to its mole fraction. Negative deviation from Raoult's law occurs when the actual vapor pressure of the solution is less than expected based on Raoult's law. This typically happens due to stronger solute-solvent interactions compared to solute-solute and solvent-solvent interactions.

Let us analyze each option:

(1) Water and Ethanol: Both form hydrogen bonds with each other, but these are weaker than the water-water hydrogen bonds. So, Raoult's law is generally followed or shows slight positive deviation.

(2) Ethanol and Acetone: Again, both can form hydrogen bonds with each other and with water. However, the interactions are not strong enough to cause a significant negative deviation. Raoult's law may be followed or have a slight positive deviation.

(3) Acetone and Chloroform: These form strong intermolecular attraction forces due to dipole-dipole interactions. These interactions are stronger than the individual solute-solute and solvent-solvent interactions, leading to a decrease in vapor pressure and negative deviation from Raoult's law.

(4) Carbondisulphide and Acetone: Carbondisulphide is nonpolar and has weak intermolecular forces. Due to the lack of strong interactions, Raoult's law is usually followed or may have slight positive deviation.

Therefore, the option that shows a negative deviation from Raoult's law is: (3) Acetone and Chloroform