Question

Lake Test of $A{l^{3 + }}$ ion is based on adsorption of blue litmus on solid surface of:
\[
  A.{\text{ }}Al \\
  B.{\text{ }}Al{\left( {OH} \right)_3} \\
  C.{\text{ }}A{l_2}{O_3} \\
  D.{\text{ }}AlC{l_3} \\
 \]

Answer 1

Hint- In order to deal with this question, we will first see the reactions involved in the lake test and the process going on and its uses. On the basis of these reactions and the processes we will select the appropriate option.

Complete answer:
Blue lake test:
To the mixture given, add water, and then add ammonium chloride followed by ammonium hydroxide. White ppt. is formed which confirms $A{l^{3 + }}$ .
This ppt. is dissolved in HCl. a colorless solution is obtained.
\[Al{\left( {OH} \right)_3} + 3HCl \to AlC{l_3} + 3{H_2}O\]
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.
Hence, Lake Test of $A{l^{3 + }}$ ion is based on adsorption of blue litmus on solid surface of \[Al{\left( {OH} \right)_3}\]

So, the correct answer is option B.

Additional information - Aluminum is noteworthy for its low density and its ability to resist corrosion by the passivation process. Aluminum and its alloys are essential to the aerospace industry, and are significant in the automotive and building sectors, such as façade design and window frames. The most important components in aluminium are the oxides and sulfates.

Note- Lake test of $A{l^{3 + }}$ ion is based on adsorption of blue litmus on solid surface of \[Al{\left( {OH} \right)_3}\] . The dye aluminum is adsorbed by the gelatinous \[Al{\left( {OH} \right)_3}\] precipitate to form lake colored solution. This test is used as a confirmatory test for $A{l^{3 + }}$ after precipitation of \[Al{\left( {OH} \right)_3}\] with aqueous ammonia.