Verification of aldehydes with Tollens' test

Chemicals needed

Ammonia solution 10% C    N    R 24-50     S (1/2)-26-36/37/29-45-61

benzaldehyde Xn    R 22    S (2)-24

sodium hydroxide solution 7,5%  C    R 35     S (1/2)-26-37/39-45

silver nitrate solution, verdünnt  Xi   N    R 34-50/53     S(1/2)-26-45-60-61

One can also verify other aldehydes, in this case heating may be necessary.

Equipment needed

test tube

Test procedure

• Safety goggles!
• One adds about 0.5 ml diluted silver nitrate solution into a test tube and then adds ammonia solution 10% until the initially formed deposit is dissolved.
• Now one adds some drops of diluted sodium hydroxide solution and then some drops of benzaldehyde and sways back and forth a bit.
• Elementary silver precipitates and is then deposited on the test tube("silver mirror") and in the solution.

Disposal

• The reaction mixture, especially the solid silver residue, is to be disposed of as silver-containing waste or as heavy metal wast.

Elucidation

Due to the addition of ammonia, silver(I) which would otherwise be precipitated as hydroxide, is complexed. The proof is based on the reducing character of aldehydes and is therefore not restricted to these. The aldehyde is oxidized to carboxylic acid, while silver(I) is reduced to silver(0).

Photos

Elementary silver precipitates

Literature

Reference will be added