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NSWChemistryQuick questions
Module 8: Applying Chemical Ideas
Quick questions on Tests for unsaturation, hydroxyl and carboxyl groups explained: HSC Chemistry Module 8
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 bromine water?Show answer
Shake the unknown with a few drops of orange bromine water. An alkene rapidly decolourises the orange to colourless by adding across the double bond:
What is selectivity caveat?Show answer
Permanganate also oxidises aldehydes, primary and secondary alcohols, and some aromatic side chains. So a positive permanganate test alone does not prove an alkene. Bromine water at room temperature is more specific.
What is sodium metal?Show answer
Drop a small piece of clean sodium into the unknown (dried). An alcohol releases hydrogen gas and forms a sodium alkoxide:
What is ester formation?Show answer
Heat the unknown with a carboxylic acid (ethanoic acid) and a few drops of concentrated . A sweet, fruity smell indicates ester formation, confirming an alcohol. Reverse the reagents to confirm a carboxylic acid.
What is sodium carbonate?Show answer
Add solid or to the unknown dissolved in water (or to the neat liquid). Brisk effervescence of indicates a carboxylic acid:
What is reactive metal?Show answer
Magnesium ribbon dissolves in a carboxylic acid solution with hydrogen evolution:
What is esterification?Show answer
Warm with an alcohol and concentrated ; the fruity ester smell confirms the carboxyl group.
What is q1?Show answer
State the observation for each of: (a) hex-1-ene plus bromine water, (b) ethanol plus acidified dichromate, (c) ethanoic acid plus sodium hydrogen carbonate. [3 marks]
What is q2?Show answer
A 0.225 g sample of an unknown monoprotic carboxylic acid neutralises 30.40 mL of 0.100 mol L NaOH. Calculate the molar mass and identify the most likely candidate (methanoic 46, ethanoic 60, propanoic 74, butanoic 88). [3 marks]
What is q3?Show answer
A student is given three unlabelled liquids X, Y and Z. X decolourises bromine water. Y effervesces with sodium hydrogen carbonate.