DSE Chemistry | Organic Chemistry Tutor Prep Guide

DSE Chemistry | Organic Chemistry Tutor Prep Guide | Functional Groups and Tests

2026-11-01

Tutor lesson-prep guides · Secondary Chemistry

Students freeze at a structure full of lines. Teach them to find the functional group first and count the carbon chain second: the group decides the chemistry, the chain decides the name, and the two jobs stay separate.

Objectives — Students can: (1) identify alcohols, aldehydes, ketones, carboxylic acids and esters from a structure; (2) choose bromine water, sodium hydrogencarbonate or Tollens reagent and state the evidence; (3) calculate the mass of ester from moles and percentage yield.

01 Prerequisites (3-minute check)

If any of these fails, fix it before the lesson starts.

Skill	Quick check	Pass mark
Relative molecular mass	Mr of C2H5OH	46
Mole	Mass of 0.10 mol of ethanol	4.6 g
Reversible reactions	Why esterification is refluxed	to push the equilibrium and raise yield

02 Lesson flow (60 minutes)

Time	Stage	Tutor does	Student does
0-8 min	Recall general formulae	alkane CnH2n+2, alkene CnH2n	student writes C3H8
8-20 min	Five functional groups	alcohol, aldehyde, ketone, acid, ester	student circles the group
20-32 min	Three tests	bromine water, NaHCO3, Tollens	student matches four tubes
32-44 min	Esterification calculation	0.10 mol ethanol with 0.10 mol acid	theory 8.8 g
44-54 min	Percentage yield	actual 5.72 g	yield 65 percent
54-60 min	Exit check	three questions collected and marked	done independently

03 Teaching script (read it out)

Scene 1: Find the group, then count the carbons

Homologues differ by CH2: C3H8 (Mr 44) and C4H10 (Mr 58) differ by 14, which is exactly CH2. Teach students to work backwards from a difference of 14 instead of memorising names.

Board focus: Find the group, then count the carbons

Scene 2: Three reagents, three pieces of evidence

Bromine water decolourises with a C=C; sodium hydrogencarbonate fizzes with a COOH group; Tollens gives a silver mirror with an aldehyde. Insist on the pattern “what I saw, therefore what it is”, not just the reagent name.

Board focus: Three reagents, three pieces of evidence

Scene 3: Esterification: limiting reagent and yield

0.10 mol of ethanol (4.6 g) with 0.10 mol of ethanoic acid (6.0 g) is a 1:1 mixture, so the theoretical yield is 0.10 mol of ethyl ethanoate = 8.8 g (Mr 88). The actual mass is 5.72 g, a yield of 65 percent. Point out that esterification is reversible, so the yield is never complete.

Board focus: Esterification: limiting reagent and yield

04 Question types and worked steps

Type	Example	Steps	Answer
Identification	functional group	circle OH, CHO or COOH	name the class
Identification	three unknown liquids	add each reagent and read the sign	write a conclusion sentence
Calculation	theoretical mass of ester	n x Mr	8.8 g
Calculation	percentage yield	actual divided by theoretical	65 percent

Sanity check (teach this): Both alcohols and carboxylic acids contain an OH, but only the acid has it attached to a C=O. Aldehydes and ketones both contain C=O, and only the aldehyde carries an H on that carbon. Always calculate yield from the limiting reagent, never from the combined mass.

05 Independent practice (3 questions)

Question	Answer	What to watch
Mr of C4H10	58	12 x 4 + 10
Theoretical mass of 0.10 mol of ethyl ethanoate	8.8 g	0.10 x 88
Percentage yield when 5.72 g is obtained	65 percent	5.72 / 8.8
Distinguish ethanoic acid from ethanol	NaHCO3 fizzes with the acid	carbon dioxide released

06 Common mistakes and what to say

Mistake	Student writes	Say this
Calling a ketone an aldehyde	claiming a silver mirror for a ketone	“A ketone has no CHO. Tollens will not react; use 2,4-DNP to show the carbonyl first.”
Dividing by the total mass	using 10.6 g as the denominator	“The denominator is the moles of limiting reagent, not the two masses added together.”
Confusing homologous with isomeric	calling C4H10 and C4H8 homologous	“Homologues differ by CH2. These differ by H2, so they are in different series.”
Forgetting esterification is reversible	quoting a yield of 100 percent	“It is reversible, so a real preparation lands around sixty to seventy percent.”

07 Homework (paper, section and question numbers)

DSE Chemistry practice paper (organic chemistry) — Q12-Q14
DSE Chemistry practice paper (identification) — Q15-Q16

08 Exit check (last 5 minutes)

Question	Answer	Decision
Mr of C4H10	58	correct means ready for polymers
Theoretical mass of 0.10 mol of ethyl ethanoate	8.8 g	wrong means redrill n x Mr
How to tell an aldehyde from a ketone	Tollens reagent	wrong means reteach functional groups

09 Tutor FAQ

How many reactions must be memorised?

The DSE organic core is the chain alcohol to aldehyde to acid to ester, which covers most questions.

How many isomers should be drawn?

C4 has two and C5 has three; questions usually ask for all of them with names.

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A TutorZone lesson-prep guide. Written by the TutorZone team; questions and lesson flow are original and are not taken from any school or publisher material.