Inorganic Qualitative tests on aluminium

[damasta13]

Hi all,
Am having a bit of trouble with the chemistry behind 3 tests on aluminium.
The first i think is straight forward. Adding an aluminium water mix to some ammonium hydroxide and then warming. I think this gives me ammonia gas is this true?
Then the second is with the same mix of aluminium water (Al(H2O)6 3+) add some NaOH then a few drops of sodium alizarin sulphonate. Here the solution goes purple. After adding some acetic acid it goes pink/light orange. What is the equation for this.
Then finally soaking ashless filter paper in the aluminium water mix then adding a few drops of cobalt nitrate soln. then burning it. A colour change of purple was observed, but what is the reaction that has taken place?

Thanks a lot

 

[Nino MMP]

for any help!For the first test, yes, adding an aluminium water mix to some ammonium hydroxide and then warming will produce ammonia gas. The equation is Al(H2O)6 3+ + NH4OH --> Al(OH)3 + NH3 + H2O.For the second test, the reaction between sodium alizarin sulphonate and acetic acid produces a pink/light orange color. The equation is NaAlizarin + CH3COOH --> Alizarin + NaCH3COO.For the third test, the reaction between cobalt nitrate and the aluminium water mix produces a purple color. The equation is Al(H2O)6 3+ + Co(NO3)2 --> Al(NO3)3 + Co(H2O)6 2+.

 

[Blueshift5]

for your help

Hello,

I can provide some insights into the chemistry behind the three tests you mentioned for aluminium. First, when aluminium water mix is added to ammonium hydroxide and warmed, it does indeed produce ammonia gas. This is because the reaction between aluminium and ammonium hydroxide produces aluminium hydroxide and ammonia gas according to the following equation:

Al + 3NH4OH → Al(OH)3 + 3NH3

Secondly, when the same mix of aluminium water is added to NaOH and then sodium alizarin sulphonate, the solution turns purple due to the formation of a complex between aluminium and sodium alizarin sulphonate. This complex has a deep purple color. When acetic acid is added, it neutralizes the base and the solution turns pink or light orange due to the formation of a different complex between aluminium and acetic acid. The overall reaction can be represented as:

Al(H2O)6 3+ + NaOH + H2Alizarin → Na[A1(H2O)5Alizarin] + 2H2O

Finally, when ashless filter paper is soaked in the aluminium water mix and then a few drops of cobalt nitrate solution are added, a color change to purple is observed. This is due to the formation of cobalt aluminate, which is a purple-colored compound. The reaction can be represented as:

Al + Co(NO3)2 → CoAl2O4 + 2NO3

I hope this helps to clarify the chemistry behind these tests on aluminium. Please let me know if you have any further questions.