Question

Why have detergents replaced soap ?

Hint:

The number one reason to remember is hard water. Soaps form scum in hard water, while detergents do not. This makes detergents much more effective for general cleaning and laundry.

Answer 1

Detergents have largely replaced soaps for cleaning purposes, especially for laundry, primarily because of their superior performance in hard water.
\begin{enumerate} \item Effectiveness in Hard Water: \[\begin{array}{rl} \bullet & \text{Soaps: Hard water contains dissolved calcium (\(Ca^{2+}\)) and magnesium (\(Mg^{2+}\)) ions. Soaps react with these ions to form an insoluble, sticky precipitate called scum. This scum reduces the cleaning ability of the soap and leaves a deposit on fabrics.} \\ \bullet & \text{Detergents: Detergents are synthetic cleaning agents whose calcium and magnesium salts are soluble in water. Therefore, detergents do not form scum in hard water and maintain their cleansing action.} \\ \end{array}\] \item Effectiveness in Acidic Water: Soaps are salts of weak acids (fatty acids) and can be decomposed by acidic water, reducing their effectiveness. Detergents are generally salts of strong acids and are not affected by the acidity of water. \item Stronger Cleansing Action: Detergents can be formulated to have a stronger cleansing action than soaps, making them more effective for a wider range of stains and fabrics. \end{enumerate} Due to these advantages, particularly their effectiveness in hard water, detergents are more widely used than soaps.