Question

A student takes 4 mL of distilled water in each of four test tubes I, II, III, and IV and then dissolves equal amount of four different salts namely $\mathrm{NaCl}\mathrm{in}\mathrm{I},{\mathrm{CaCl}}_2\mathrm{in}\mathrm{II},{\mathrm{MgCl}}_2\mathrm{III},\mathrm{and}\mathrm{KCl}\mathrm{in}\mathrm{IV}$.He then adds 8 drops of the given soap solution to each test tube and shakes the contents of the test tube 10 times. In which test tubes enough lather(foam) will be formed?

• A. I and II
• B. II and III
• C. I and IV
• D. III and IV

Answer 1

The correct option is C

I and IV

The explanation for the correct option:

C: I and IV

• Soaps are long-chain carboxylic acids that are composed of Sodium and Potassium salts.
• Soaps react with Calcium and Magnesium salts to form insoluble precipitates.
• These insoluble precipitates are known as scum and due to the presence of scum water gets harder.
• The hard water will not form enough lather(foam) to clean the clothes.
• The Sulphates, Bicarbonates, and Chlorides of Calcium and Magnesium when mixed with water do not create much lather(foam).
• The reaction of soap with Sodium and Potassium salt will easily dissolve in water and forms a neutral solution.
• The Sodium and Potassium salts will create enough lather to wash the clothes.
• The reaction between Ester and alkali produces soaps and Glycerol.
• The process is known as saponification.

$\underset{\left(\mathrm{Ester}\right)}{\mathrm{Fat}\mathrm{or}\mathrm{oil}}+\underset{(\mathrm{Sodium}\mathrm{hydroxide})}{\mathrm{NaOH}\left(\mathrm{s}\right)}\stackrel{\mathrm{Heat}}{\to }\underset{(\mathrm{Sodium}\mathrm{salt}\mathrm{of}\mathrm{fatty}\mathrm{acids})}{\mathrm{Soap}}+\underset{(\mathrm{An}\mathrm{alcohol})}{\mathrm{Glycerol}}$

By this, we concluded that $\mathrm{NaCl}\mathrm{in}\mathrm{I}\mathrm{and}\mathrm{KCl}\mathrm{in}\mathrm{IV}$will react with water to form enough lather(foam) after shaking.

Hence, option C $\mathbf{NaCl}\mathbf{}\mathbf{in}\mathbf{}\mathbf{I}\mathbf{}\mathbf{and}\mathbf{}\mathbf{KCl}\mathbf{}\mathbf{in}\mathbf{}\mathbf{IV}$ is correct.