En anglais

Aldehydes, ketones and their tests

Science · Chemistry · ages 17-18

Name ______________________ Date ____________

What does Tollens reagent do to an aldehyde and to a simple ketone such as propanone?
- Mirrors both of them
- Mirrors neither of them
- Mirrors aldehydes only
Why does a nucleophile attack the carbonyl carbon?
- It carries a partial positive charge
- The carbon carries a full negative charge
- The oxygen pushes nucleophiles onto carbon
Fehling solution stays blue with simple ketones such as propanone but turns brick red with aldehydes.
Circle one: True False
Propanal reacts with cyanide. Why do equal amounts of both mirror forms appear?
- Both faces are equally open
- The cyanide used is already a mixture
- The product keeps flipping between forms
What happens to the carbonyl double bond when cyanide adds?
- It stays exactly as it was
- It breaks; CN bonds to carbon
- It moves onto the oxygen alone
What does reduction give for propanal and for propanone?
- Primary alcohol from propanal, secondary alcohol from propanone
- Secondary alcohol from propanal, primary alcohol from propanone
- A carboxylic acid from both of them
A student draws only one mirror form from cyanide addition to propanal and calls it complete. What is missing?
- Its twin from the other face
- A second cyanide adding to the same carbon
- The water molecule that splits the product
An unknown gives no mirror with Tollens but reddens Fehling. A student calls it a ketone. What is wrong?
- Nothing is wrong, since simple ketones redden Fehling
- Fehling rules out a simple ketone; repeat Tollens
- Both tests always agree, so the sample must be water

Answer key

For grown-ups. Fold this page away before handing over the rest.

Aldehydes, ketones and their tests W1-mt_bVcJ0UaXk6-s1

Mirrors aldehydes only · Aldehydes oxidise further and plate the mirror, while simple ketones such as propanone resist.
It carries a partial positive charge · Oxygen drags electrons away, leaving carbon short of electrons and open to attack.
True · Aldehydes reduce the blue mixture to a brick-red solid, and a simple ketone such as propanone does not. The sentence is true.
Both faces are equally open · The flat carbonyl of propanal shows two equal faces, and its new carbon holds four different groups, so both attacks give mirror forms equally often.
It breaks; CN bonds to carbon · The double bond opens so CN can bond to carbon and oxygen becomes OH.
Primary alcohol from propanal, secondary alcohol from propanone · Aldehydes reduce to primary alcohols and ketones to secondary alcohols.
Its twin from the other face · Both faces react equally, so with propanal the product is always the pair, never one alone.
Fehling rules out a simple ketone; repeat Tollens · Brick red with Fehling rules out a simple ketone such as propanone. An aldehyde, or one of the few ketones that reddens Fehling, would give a Tollens mirror too, so the Tollens run went wrong.