How does Tollens' test works?

1 Answer
anor277
Apr 16, 2016

Tollens' test exploits the ability of silver ion to oxidize aldehydes and primary alcohols to give carboxylic acids.

Explanation:

Reduction half equation:

#Ag^(+) + e^(-) rarr Ag(s) darr# #(i)#

Oxidation half equation:

#RC(=O)H + H_2O rarr RC(=O)OH + 2H^(+) + 2e^-# #(ii)#

Overall, #2xx(i)+(ii)#

#2Ag^(+) + RC(=O)H + H_2O rarr 2Ag(s) +RC(=O)OH + 2H^(+) #

Both primary alcohols, and aldehydes can be oxidized to carboxylic acids using #Ag^+#, and this test is commonly used to differentiate aldehydes from most ketones (the test does give a positive for cyclohexanone). Using scrupulously clean glassware, you can get a beautiful silver mirror lining the inside of your glass. In fact the best mirrors (i.e. looking glasses) are still made with this reaction.

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