IP Chemistry Upper Sec 05: Acid-Base Chemistry

Study guide26 Nov 2025, 00:00 Z

Acids, bases, salts, and ammonia fundamentals for IP Sec 3-4 Chemistry (O-Level 6092, 2026).

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These notes align with SEAB GCE O-Level Chemistry (6092) content used in IP programmes (exams from 2026).

Status: SEAB O-Level Chemistry 6092 syllabus (exams from 2026) checked 2026-06-02 - scope unchanged; remains the reference for this note.

6092 Route Map

Use this page for Topic 5 Acid-Base Chemistry: acids, alkalis, salts, ammonia, neutralisation, and salt-preparation route choice.

Need	Best Eclat page
Official 6092 paper format and topic order	O-Level Chemistry 6092 syllabus guide
Sec 3 foundation overview before acid-base work	Sec 3 Chemistry notes
Detailed salt-preparation practical routine	O-Level Chemistry Salt Preparation Playbook
QA table and reagent observations	O-Level Chemistry QA table toolkit
Titration table and average titre	O-Level Chemistry titration table playbook

The core idea is simple: Acid-base questions usually ask what reacts and what salt forms.

Use it as a working check: Identify the acid, base or carbonate, write the salt from the ions, then choose a preparation route based on solubility.

Then go one layer deeper: Example: make copper sulfate crystals by adding excess copper oxide to warm dilute sulfuric acid, filtering off excess solid, then crystallising the filtrate.

Reviewed by

Azmi·Senior Chemistry Specialist

Sources

SEAB GCE O-Level Chemistry (6092) syllabus (examinations from 2026)

Step	What to write	Example for aluminium sulfate
1. Name the cation from the metal, base, or alkali	$\ce{Al^{3+}}$	Aluminium supplies $\ce{Al^{3+}}$ .
2. Name the anion from the acid	$\ce{SO4^{2-}}$ from sulfuric acid	The acid supplies sulfate, not sulfur.
3. Balance charges to get the formula	$\ce{Al2(SO4)3}$
4. Then choose the preparation route	Insoluble base plus dilute acid, titration, or precipitation	Route choice depends on solubility, not on the salt name alone.

Target salt type	Best route	Why this route works	Common trap
Soluble salt, cation from an insoluble oxide, hydroxide, or carbonate	Add excess solid to warm dilute acid, filter, crystallise	Excess solid ensures all acid is used up; filtration removes the unreacted solid	Leaving acid behind because the solid was not in excess
Soluble salt, cation from an alkali such as $\ce{NaOH}$ or $\ce{KOH}$	Titration, then repeat without indicator and crystallise	Both reactants are soluble, so excess reagent cannot be removed by filtration	Evaporating a solution that still contains indicator
Insoluble salt	Precipitation from two soluble solutions, then filter and wash	The desired salt forms as a solid immediately	Choosing two reagents that introduce the wrong ions

Stage	What to do	Why it matters	Common trap
Concentrate the filtrate	Heat gently until the solution is near saturation.	This removes some water while keeping the salt dissolved.	Boiling to dryness and decomposing or splattering the salt.
Test whether it is concentrated enough	Let a drop on a cool tile form crystals, or look for crystals starting at the edge if that method is taught.	The solution is ready to crystallise on cooling.	Stopping while the solution is still too dilute.
Cool the solution	Leave it to cool so crystals form slowly.	Slow cooling gives cleaner crystals.	Filtering immediately while all the salt is still dissolved.
Collect and dry crystals	Filter, wash with a little cold distilled water, then dry between filter papers.	Washing removes soluble impurities without dissolving too much product.	Washing with hot water or using too much water.

Acid-base pair	End-point region	Good indicator choice	Common trap
Strong acid plus strong base	Near pH 7	Methyl orange or phenolphthalein	Do not choose from memory before naming both reagents.
Weak acid plus strong base	Above pH 7	Phenolphthalein	Methyl orange changes too early for this pair.
Strong acid plus weak base	Below pH 7	Methyl orange	Phenolphthalein changes too late for this pair.

Step	What to write	Why it matters
Prepare	Warm an ammonium salt with a strong alkali.	The alkali releases ammonia from ammonium ions.
Collect	Use downward displacement of air.	Ammonia is very soluble in water, so collection over water loses the gas.
Test	Hold moist red litmus paper near the gas.	Ammonia dissolves in the water on the paper and turns it blue.
Confirm	Note the sharp, choking smell only if the question asks for observation.	Smell is supporting evidence, not the main chemical test.

IP Chemistry Upper Sec 05: Acid-Base Chemistry

6092 Route Map

Sources

What you must know

Salt Formula Checkpoint

Salt Preparation Route Map

Worked Example: Choosing the Route

Crystallisation endpoint checkpoint

Indicator Choice Checkpoint

Detailed notes

Ammonia gas handling checkpoint

Quick applications

Exam cues

Practice drills

Next steps

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