Common misconceptions › Class 12 › Chemistry › Aldehydes, Ketones and Carboxylic Acids Class 12 Chemistry · Chapter 8 · NCERT (lech203)
Aldehydes, Ketones and Carboxylic Acids: common misconceptions
See the tempting mistake students make in Aldehydes, Ketones and Carboxylic Acids, why it feels right at first glance, and a worked visual example that shows the right idea.
Worked visual “If your child says…” (6) Teach & practice The tempting mistake & worked visual Will every carbonyl compound give a silver mirror? Wrong
Both ethanal and propanone give a positive Tollens test because both have C=O.
Why it feels right. I treat all carbonyl groups as having identical chemical behaviour.
Right
Under ordinary Tollens test conditions, an aldehyde such as ethanal can be oxidised. A simple ketone such as propanone does not give the same result.
Worked example
Ethanal
Tollens reagent → Silver mirror can form
Propanone
Same test → No silver mirror
Both contain C=O, but only ethanal gives the silver mirror in this comparison. Test ethanal and propanone separately. Ethanal reduces the silver complex and can leave silver on the tube. Propanone gives no silver mirror in this comparison. If your child says… (6 concept checks in this chapter)
As you work through Aldehydes, Ketones and Carboxylic Acids , listen for these everyday misunderstandings and use the prompt alongside each one.
If your child says…
“A carbonyl group always makes an aldehyde.”
Ask together Does each carbonyl carbon have a hydrogen attached? What’s true The atoms directly attached to carbonyl carbon distinguish aldehydes from ketones. If your child says…
“Oxidising ethanol always stops at ethanal.”
Ask together What could happen if the aldehyde stays with an oxidant that can oxidise it further? What’s true The oxidation conditions determine whether ethanal remains or reacts further. If your child says…
“Cyanide attaches to the carbonyl oxygen.”
Ask together Which carbonyl atom carries a partial positive charge? What’s true The electron-pair donor attacks carbonyl carbon, which becomes tetrahedral. If your child says…
“Every carbonyl compound gives a silver mirror.”
Ask together Do both compounds have a hydrogen attached directly to carbonyl carbon? What’s true Tollens’ reagent produces silver with ethanal but not propanone. If your child says…
“The hydrogen attached to carbonyl carbon is an alpha hydrogen.”
Ask together Does methanal have a carbon beside its carbonyl carbon? What’s true An alpha hydrogen belongs to the neighbouring carbon, not carbonyl carbon itself. If your child says…
“The bubbles mean the vinegar is boiling.”
Ask together Did we heat the vinegar before the bubbles appeared? What’s true This reaction releases gas without boiling the liquid. Use this chapter three ways Previous chapter Alcohols, Phenols and Ethers Next chapter Amines
In the app, your child answers a short check-in with confidence taps, and you see which of these misunderstandings showed up—and which ones are gone.
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