Question

Lake test of $A{l}^{3+}$ ion is based on adsorption of blue litmus on solid surface of

• A. $A{l}_2(C{O}_3{)}_3$
• B. $Al(OH{)}_3$
• C. $AlC{l}_3$
• D. $Al$ metal

Answer 1

The correct option is B $Al(OH{)}_3$

Blue lake test:
To the $A{l}^{3+}$ salt solution, add water, and then add ammonium chloride followed by ammonium hydroxide. White precipitate is formed which confirms $A{l}^{3+}$ .
This precipitate is dissolved in HCl, a colorless solution is obtained.
$Al(OH{)}_3+3HCl\to AlC{l}_3+3H_{2}O$

Then 2 drops of blue litmus solution is added. Red color is obtained. And ammonium hydroxide is added to make the solution alkaline so that ammonium hydroxide is formed.
As soon as the solution becomes alkaline, blue floating precipitate is obtained.
Then the blue litmus solution is adsorbed on this aluminum hydroxide.
This is the principle for this test, Aluminum hydroxide is a good adsorbent, and therefore it adsorbs the blue litmus solution and gives this blue lake test.