Question

A student takes four test tubes marked P, Q, R and S of 25 mL capacity and fills 10 mL of distilled water in each. He dissolves one spoon full of four different salts in each as − KCl in P, NaCl in Q, CaCl₂ in R and MgCl₂ in S. He thenadds about 2 mL of a sample of soap solution to each of the above test tubes. On shaking the contents of each of the test tubes, he is likely to observe a good amount of lather (foam) in the test tubes marked(a) P and Q(b) R and S(c) P, Q and R(d) P, Q and S

Answer 1

In r and s lather will be observed as soaps(sodium and potassium salts) react with magnesium and calcium salts of hard water to form a insoluble precipitate called scum





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