Question

A student takes about 4mL of distilled water in four test tubes marked P, Q, R, and S. He then dissolves in each test tube an equal amount of one salt in one test tube, namely sodium sulphate in P, and potassium sulphate in Q, calcium sulphate in R and magnesium sulphate in S. After that he adds an equal amount of soap solution in each test tube. On shaking each of these test tubes well, he observes a good amount of lather(foam) in the test tubes marked.

• A. P and Q
• B. Q and R
• C. P, Q, and S
• D. P, R, and S

Answer 1

The correct option is A

P and Q

The long chain of fatty acids contains Potassium ($\mathrm{K}$) or Sodium ($\mathrm{Na}$) salts are called soaps. The soap produces insoluble precipitate with hard water having Calcium ($\mathrm{Ca}$) and Magnesium ($\mathrm{Mg}$) ions.

Thus, Sodium and Potassium sulphates form lather in (P) and (Q) test tubes.

Hence, option (A) is the correct option.