The change in O.N of Cu+2 in Fehling's test is:
Correct answer: D. 1
- A. Zero
- B. +2
- C. -2
- D. 1
Explanation
Fehling's test is used to detect the presence of reducing sugars, such as aldehydes and certain ketones. The reagent consists of two solutions: Fehling's A (copper(II) sulfate) and Fehling's B (sodium hydroxide and potassium sodium tartrate).When a reducing sugar is present, such as glucose or fructose, it can undergo oxidation. In Fehling's test, the reducing sugar reacts with the copper(II) ions in Fehling's A solution. The copper(II) ions get reduced to copper(I) ions (Cu+2 to Cu+1).This reduction of copper(II) ions to copper(I) ions results in the formation of a reddish-brown precipitate of copper(I) oxide. The change in oxidation state of Cu from +2 to +1 is a key part of the reaction that helps us detect the presence of reducing sugars.
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About Aldehydes and Ketones
Aldehydes and ketones contain the polar carbonyl group, but aldehydes are generally more readily oxidised and more reactive than ketones. Coverage includes preparation by oxidation or reduction routes, nucleophilic addition of reagents such as hydrogen cyanide and bisulfite, and tests that distinguish aldehydes from ketones.
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