Micelle Properties: Identifying the Incorrect Statement

The question asks to identify the statement about micelles that is incorrect. Let's analyze each statement:

• Statement 1: Soap molecules are sodium or potassium salts of long-chain carboxylic acids.

  This statement is correct. Soaps are typically formed from the saponification of fats and oils, yielding sodium or potassium salts of long-chain fatty acids (e.g., sodium stearate).

• Statement 3: Grease gets collected in the centre of the micelle.

  This statement is correct. A micelle has a structure where hydrophobic tails point inwards, forming a non-polar core, and hydrophilic heads face outwards towards the water. Grease (oils and fats) is non-polar and is thus solubilized within the hydrophobic core of the micelle.

• Statement 4: Soap micelles scatter light.

  This statement is correct. Micelles are aggregates of molecules, making them larger than individual molecules. These colloidal-sized particles are capable of scattering light, a phenomenon often observed as the Tyndall effect.

• Statement 2: Micelles precipitate out of solution because of ion-ion repulsion.

  This statement is incorrect. Micelles form stable aggregates in water. The hydrophilic heads of the soap molecules have charges (e.g., \(-\text{COO}^-\) groups). While there is ion-ion repulsion between these charged heads, this repulsion actually helps to keep the micelles dispersed in the solution and prevents them from aggregating too closely. Precipitation occurs due to other factors, such as exceeding solubility limits or changes in conditions (like adding salt), but not primarily because ion-ion repulsion forces them to precipitate.

Therefore, the statement that is not correct regarding micelles is that they precipitate out of solution because of ion-ion repulsion.