Question

38) Which of the following substances does not form a curdy precipitate when it is added to hard water.

• A. potassium salt of fatty acid
• B. sodium salt of fatty acid
• C. sodium lauryl sulfate
• D. none of the above

Answer 1

The correct option is C

sodium lauryl sulfate

Explanation of the correct option:

Curdy precipitate refers to scum. When we use soap in hard water then lather is not formed, because of presence of magnesium and calcium salts present in hard water. Instead soap form scum with hard water. Detergents forms lather with hard water.

(C) Sodium lauryl sulfate is a detergent and hence it forms lather with hard water and not scum (cloudy precipitate).

Explanation of the incorrect options:

(A) Potassium salt of fatty acid is a soap hence it forms scum.

(B) Sodium salt of fatty acid is a soap hence it forms scum.

Hence, the correct option is (C).