s-Block ElementsMedium

Question

Which of the following will form foam in water containing ${Ca}^{2 +}$ and ${Mg}^{2 +}$ ions?

Options

A.Ba-stearate
B.Na-palmitate
C.Potassium n-dodecyl benzene sulphonates
D.All of these

Solution

Sol. Key concept: Synthetic sulfonate detergents remain effective in hard water.

Ca²⁺ and Mg²⁺ react with ordinary fatty-acid soaps to form poorly soluble calcium/magnesium carboxylates, producing scum and reducing lather. Sodium palmitate is such a soap, while barium stearate is itself poorly soluble.

Potassium n-dodecylbenzene sulfonate is an anionic synthetic detergent. Its sulfonate head group does not form the same insoluble soap scum under normal washing conditions, so it can produce foam in hard water. Hence option (c).

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