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NSWChemistryQuick questions
Module 7: Organic Chemistry
Quick questions on Aldehydes, ketones and carboxylic acids explained: HSC Chemistry Module 7
10short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What is the three functional groups?Show answer
All three contain a carbonyl group $C=O$. They differ in what else is attached to the carbonyl carbon.
What is formation?Show answer
The oxidant is acidified $K_2Cr_2O_7$ (orange to green) or acidified $KMnO_4$ (purple to colourless). To stop a primary alcohol at the aldehyde, distil the aldehyde off as it forms (aldehydes have lower boiling points than alcohols). To go to the acid, reflux with excess oxidant.
What is physical properties?Show answer
Boiling point trend (same carbon number): alkane < aldehyde/ketone < alcohol < carboxylic acid.
What is tests that distinguish aldehyde from ketone?Show answer
Tollens' reagent (silver mirror test). $[Ag(NH_3)_2]^+$ in alkaline solution. Warm gently in a clean glass test tube.
What is reactions of carboxylic acids?Show answer
Carboxylic acids are weak acids ($pK_a$ about 4 to 5). They ionise partially in water:
What is distinguishing all four classes?Show answer
A flowchart that handles alcohol, aldehyde, ketone, carboxylic acid:
What is writing a positive Tollens' for a ketone?Show answer
Ketones do not give a silver mirror. Only aldehydes do.
What is forgetting the cyclic dimer?Show answer
When explaining the high boiling point of carboxylic acids, mention the dimer explicitly; it is what marks the answer.
What is oxidising a carboxylic acid further?Show answer
Under HSC conditions, carboxylic acids are the terminus of the oxidation pathway. They do not go further.
What is naming a propanone "propan-2-one" only?Show answer
Acetone and propan-2-one are both accepted but the IUPAC name is propan-2-one (or simply propanone, since the locant is unambiguous on a 3-carbon chain).