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SEC 2027 · K324 SEC 3 · PURE CHEMISTRY replaces 6092

Sec 3 Pure Chem
Visual Notes

Pictures first. Words second. Built from the SEC K324 (Pure Chemistry) syllabus.

HOW TO STUDY WITH THIS

Read the 💡 box
One sentence = the whole topic. Say it out loud.

Study the picture
Cover it, then redraw it from memory.

Learn the yellow
Highlighted words = exam keywords.

Copy the ✍ box
That's the exact sentence to write in exams.

WHAT THE BOXES MEAN

BIG IDEAThe one thing to understand first

✍ WRITE THISExact exam wording to memorise

⚠ TRAPWhere people lose marks

🧠 HOOKTrick to remember it

THE 9 SEC 3 TOPICS

🔬

TOPIC 1 · p.2

Experimental

Pick the method by asking what is mixed with what.

🫧

TOPIC 2 · p.4

Kinetic Particles

Particles always move. More heat = faster.

⚛️

TOPIC 3 · p.5

Atomic Structure

Protons = which element. Electrons = how it reacts.

🔗

TOPIC 4 · p.6

Bonding

Atoms bond to get a full outer shell.

✏️

TOPIC 5 · p.9

Formulae & Equations

Charges cancel to zero. Atoms in = atoms out.

🍋

TOPIC 6 · p.10

Acids & Bases

H⁺ + OH⁻ → H₂O is neutralisation.

🔍

TOPIC 7 · p.12

Ion & Gas Tests

Add reagent → see colour → name the ion.

🧮

TOPIC 8 · p.13

Calculations

Everything goes through MOLES.

🗺️

TOPIC 9 · p.15

Periodic Table

Same group = same outer electrons.

✏️Practical & drawing

Titration, crystallisation, how to draw, exam words.

🎨Quick-ID page

Cation flowchart + every colour.

📖Definitions

Word-perfect, keywords highlighted.

📅 SEC 4The rest of K324 (redox, energetics, rates, reactivity series & metals, organic, air) is usually taught in Sec 4 — not in these notes.

🖨 PRINTCtrl+P → Save as PDF · Scale 100% · Margins None · Background graphics ON

Sec 3 Pure Chemistry · SEC K324

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1

Experimental Chemistry

Part A · Separating mixtures

BIG IDEAPick the method by asking: what is mixed with what?

Which method? Just match the mixture

If you have…	Use…	Because…
🏖️ insoluble solid + liquid sand + water	Filtration	solid can't pass through filter paper
🧂 dissolved solid — want the SOLID salt from salt water	Evaporation / Crystallisation	water leaves, solid stays. Crystallise if solid breaks down on heating
🏖️🧂 2 solids, only one dissolves sand + salt	Dissolve → filter → evaporate	add water + stir; sand is the residue, salt is in the filtrate
🧊 one solid sublimes iodine, ammonium chloride	Sublimation	solid → gas → solid on a cold surface
💧 dissolved solid — want the LIQUID pure water from sea water	Simple distillation	solvent boils off, condenses back to liquid
🍷 2 liquids that MIX ethanol + water	Fractional distillation	different boiling points (lowest comes out first)
🎨 coloured dyes / inks	Chromatography	different solubility in solvent → travel different distances

The 3 diagrams you must draw

Filtration — residue stays on paper, filtrate passes through

Distillation — cold water enters at the bottom of condenser

Chromatography — R_f = a ÷ b · mix contains dye X

⚠ TRAPBaseline in pencil, not pen (ink would dissolve and run). Baseline must be above the solvent level.

🧠 HOOKR_f is less than 1, no units. Same R_f + same colour = same substance. Colourless spots? Spray a locating agent.

✍ WRITE THIS"Fractional distillation separates liquids with different boiling points. The liquid with the lowest boiling point distils over first."

Sec 3 Pure · Topic 1 · Experimental Chemistry

⚗️

1

Experimental Chemistry

Part B · Apparatus, gases & purity

Measuring volume — accuracy ladder

🥛Beakerrough only

📏Measuring cylinder±0.5 cm³

🧪Buretteany volume
to 0.05 cm³

💉Pipetteone fixed volume
e.g. 25.0 cm³

❌ least accuratemost accurate ✅

⏱ time → stopwatch (s)🌡 temp → thermometer (°C)⚖ mass → balance (g)🎈 gas volume → gas syringe (cm³)

Collecting gases — 3 ways

Over water
gas insoluble in water
H₂O₂CO₂

Upward delivery
less dense than air
H₂NH₃

Downward delivery
denser than air
CO₂Cl₂SO₂HCl

Drying gases

Drying agent	Dries	Do NOT use for
Concentrated sulfuric acid	most gases	NH₃ (alkaline — reacts)
Calcium oxide (quicklime)	NH₃	acidic gases (CO₂, SO₂, HCl)
Fused calcium chloride	most gases	NH₃

Is it pure?

Impurity → lowers m.p., raises b.p. & melts over a range

✅3 signs it's pure

① sharp, fixed melting point
② sharp, fixed boiling point
③ one spot on a chromatogram

✍ WRITE THIS"A pure substance has a fixed, sharp melting and boiling point."

🧠 HOOKTo identify a substance: measure its m.p. or b.p. and compare with known data. A match = same substance.

Sec 3 Pure · Topic 1 · Experimental Chemistry

🫧

2

Kinetic Particle Theory

Solids, liquids, gases & how they change

BIG IDEAAll matter is tiny particles that never stop moving. More heat → more energy → faster.

SOLID 🧊 packed · vibrate in place

LIQUID 💧 close, random · slide past

GAS 💨 far apart · move fast, randomly

	🧊 Solid	💧 Liquid	💨 Gas
Forces of attraction	very strong	strong	very weak
Fixed shape?	✓	✗	✗
Fixed volume?	✓	✓	✗ fills container
Can be compressed?	✗	✗	✓ lots of space
Kinetic energy	low	medium	high

Changes of state

red = takes in heat · blue = gives out heat

Heating curve

Flat part = temperature constant

✍ WRITE THIS"Temperature stays constant during melting because heat energy is used to overcome the forces of attraction between particles."

🔥Heating a substance

particles gain kinetic energy → move faster → overcome forces → melt, then boil

❄️Cooling a substance

particles lose energy → move slower → forces pull them closer → condense, then freeze

Diffusion

🌬️Diffusion is faster when…

🔥 temperature is higher (more KE)
🪶 particles are lighter (lower M_r)
NH₃ is lighter → travels further
👃 Everyday evidence: perfume / cooking smells spread across a room · a drop of ink spreads in still water → particles are moving

✍ WHY GASES COMPRESS"Gas particles are far apart with lots of space between them, so they can be pushed closer together."

Sec 3 Pure · Topic 2 · Kinetic Particle Theory

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3

Atomic Structure

Protons, neutrons, electrons, shells, isotopes

BIG IDEAProtons decide WHICH element it is. Electrons decide HOW it reacts.

Neutral atom: protons = electrons

Particle	Where	Charge	Mass
Proton	nucleus	+1	1
Neutron	nucleus	0	1
Electron	shells	−1	1/1840

Electron shells fill 2 → 8 → 8

Na = 2,8,1 → 1 outer e⁻

1H1

2He2

3Li2,1

4Be2,2

5B2,3

6C2,4

7N2,5

8O2,6

9F2,7

10Ne2,8

11Na2,8,1

12Mg2,8,2

13Al2,8,3

14Si2,8,4

15P2,8,5

16S2,8,6

17Cl2,8,7

18Ar2,8,8

19K2,8,8,1

20Ca2,8,8,2

outer electrons = Group number of shells = Period

🔄Making ions — only electrons change

Na (2,8,1) → Na⁺ (2,8) loses 1 e⁻ → positive
Cl (2,8,7) → Cl⁻ (2,8,8) gains 1 e⁻ → negative

Count protons, neutrons, electrons — atoms and ions

Particle	Protons = Z	Neutrons = A − Z	Electrons	How
²⁷₁₃Al atom	13	14	13	neutral → e = p
²⁷₁₃Al³⁺ ion	13	14	10	3+ → lost 3 e⁻
³²₁₆S²⁻ ion	16	16	18	2− → gained 2 e⁻

Isotopes

🧮Average mass (A_r)

Cl: 75% ³⁵Cl + 25% ³⁷Cl
(75×35 + 25×37) ÷ 100 = 35.5

✍ WRITE THIS"Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. They have the same chemical properties because they have the same number of outer electrons."

🧠 HOOKIon charge from group: Grp 1 → +1 · Grp 2 → +2 · Grp 13 → +3 · Grp 15 → −3 · Grp 16 → −2 · Grp 17 → −1 · Grp 18 → none (they lose/gain e⁻ to get a noble gas configuration)

Sec 3 Pure · Topic 3 · Atomic Structure

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4

Chemical Bonding

Part A · 3 bond types & their properties

BIG IDEAAtoms bond to get a full outer shell (like a noble gas).

⚡ IONIC

metal + non-metal
electrons TRANSFERRED
→ + and − ions attract

🤝 COVALENT

non-metal + non-metal
electrons SHARED
→ molecules

🌊 METALLIC

lattice of positive ions
in a "sea of electrons"
→ malleable, conducts

Structure → properties (the big table)

Structure	Melting pt	Conducts?	Example	Why (1 line)
⚡ Giant ionic	HIGH	only molten / aq	NaCl, MgCl₂	strong attraction between ions; ions only free to move when melted/dissolved
🫧 Simple molecular	LOW	✗ never	H₂O, CO₂, I₂	weak forces between molecules, no ions or free electrons
💎 Giant covalent	VERY HIGH	✗ (graphite ✓)	diamond, graphite, SiO₂	many strong covalent bonds to break
🌊 Metallic	HIGH	✓ solid + molten	Cu, Fe	delocalised electrons carry charge

NaCl lattice · Na⁺ & Cl⁻ alternate

✍ WHY HIGH M.P."Ionic compounds have a giant lattice with strong electrostatic forces between oppositely charged ions. A lot of energy is needed to overcome them."

✍ WHY LOW M.P."Simple molecular substances have weak forces between molecules, so little energy is needed to overcome them."

⚠ TRAPSimple molecular: low m.p. is because of weak forces BETWEEN molecules — NOT weak covalent bonds. The covalent bonds inside are strong!

✍ IONIC"In the solid, ions are held in fixed positions and cannot move. When molten or aqueous, the ions are free to move and carry charge."

✍ METAL"Metals are malleable because layers of ions can slide over each other while the sea of electrons holds them together."

Alloys — why they're harder

Pure metal vs alloy — different-sized atoms disrupt the layers

Alloy	Made of
Brass	copper + zinc
Stainless steel	iron + chromium (+ nickel, carbon)
Alloy = a mixture of a metal with another element. Exam may show a diagram — mixed atom sizes = alloy.

Sec 3 Pure · Topic 4 · Chemical Bonding

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4

Chemical Bonding

Part B · Dot-and-cross diagrams & types of substance

🧠 RULESShow outer shells only · • dots for one atom, × crosses for the other · Ionic = [brackets] + charge · Covalent = pairs in the overlap

Ionic

NaCl — Na gives 1 e⁻ to Cl

MgCl₂ — Mg gives 1 e⁻ to each Cl

Covalent — the 5 syllabus molecules (+1 practice)

H₂ · 1 single bond

O₂ · 1 double bond

H₂O · 2 single bonds

CH₄ · 4 single bonds

CO₂ · 2 double bonds

N₂ · triple bond (practice)

🧠 HOOKCount: 1 shared pair = single · 2 pairs = double · 3 pairs = triple. Check every atom ends with 8 (H ends with 2).

Element · compound · mixture

ELEMENT
one type of atom

COMPOUND
elements chemically joined, fixed ratio

MIXTURE
not chemically joined — can separate

Sec 3 Pure · Topic 4 · Chemical Bonding

💎

4

Chemical Bonding

Part C · Giant covalent & metallic structures

BIG IDEAGiant structure = millions of strong bonds → very high m.p. Properties come from structure.

Diamond vs graphite (both pure carbon)

	💎 Diamond	✏️ Graphite
Bonds / C	4	3
Hard?	very hard	soft — layers slide
Conducts?	✗	✓ free electron
Use	cutting tools (drill tips)	electrodes, lubricant

✍ GRAPHITE CONDUCTS"Each C is bonded to 3 others, so each has one delocalised electron that can move and carry charge."

✍ GRAPHITE IS SOFT"Layers are held by weak forces, so they can slide over each other — used as a lubricant."

Silicon dioxide (SiO₂, sand)

💎 like diamond

each Si bonded to 4 O, each O to 2 Si → giant lattice
very high m.p., hard, does not conduct, insoluble

🧠 HOOKGiant covalent = "DGS": Diamond, Graphite, Silicon dioxide. Only graphite conducts.

Compare the 3 covalent structures

Type	Example	Structure	M.p.
🫧 Simple molecular	methane, iodine	small molecules, weak forces between molecules	low
🧵 Macromolecule	poly(ethene)	very long chains, weak forces between chains → soft, flexible	fairly low
💎 Giant covalent	SiO₂, diamond, graphite	all atoms joined by strong covalent bonds	very high

Metallic bonding

lattice of positive ions in a sea of delocalised electrons

Property	Because…
High m.p.	strong attraction: + ions ↔ electrons
Conducts	delocalised electrons move
Malleable	layers of ions slide

Sec 3 Pure · Topic 4 · Chemical Bonding

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5

Formulae & Equations

Ions, writing formulae, balancing, ionic equations

BIG IDEAIn a formula, charges cancel to zero. In an equation, atoms in = atoms out.

Ion bank — memorise these

➕ POSITIVE (cations)

+1 Na⁺K⁺Li⁺Ag⁺H⁺NH₄⁺
+2 Mg²⁺Ca²⁺Zn²⁺Cu²⁺Fe²⁺Pb²⁺Ba²⁺
+3 Al³⁺Fe³⁺

➖ NEGATIVE (anions)

−1 Cl⁻Br⁻I⁻OH⁻NO₃⁻HCO₃⁻
−2 O²⁻S²⁻SO₄²⁻CO₃²⁻
−3 PO₄³⁻
-ide = just the element (chloride) · -ate = has oxygen (sulfate)

Writing a formula — swap & drop

Polyatomic ion? Use ( brackets )

Ca²⁺ + OH⁻ → Ca(OH)₂ ✓
CaOH₂ ✗ (means 2 hydrogens, wrong!)

Simplify if you can

Mg²⁺ + O²⁻ → Mg₂O₂ → MgO

From a diagram — count the atoms

H–S–H → H₂S · O=C=O → CO₂

Balancing an equation — 4 steps

Write the word equation

Write correct formulae

Add big numbers in front only

Add state symbols
(s) solid · (l) liquid · (g) gas · (aq) dissolved in water

calcium + water → calcium hydroxide + hydrogen
Ca(s) + 2H₂O(l) → Ca(OH)₂(aq) + H₂(g)

⚠ TRAPNever change the small numbers (subscripts) to balance — that turns it into a different substance.

Ionic equations — 3 steps

① Split (aq) things into ions
Ag⁺ + ~~NO₃⁻~~ + ~~Na⁺~~ + Cl⁻ → AgCl(s) + ~~Na⁺~~ + ~~NO₃⁻~~
② Cross out spectator ions (same on both sides)
③ Write what's left: Ag⁺(aq) + Cl⁻(aq) → AgCl(s)

Must-know ionic equations

H⁺ + OH⁻ → H₂O
Ba²⁺ + SO₄²⁻ → BaSO₄(s)
Cu²⁺ + 2OH⁻ → Cu(OH)₂(s)
2H⁺ + CO₃²⁻ → H₂O + CO₂
Cl₂ + 2Br⁻ → 2Cl⁻ + Br₂

🧠 HOOKElements that exist as pairs (diatomic): H₂ N₂ F₂ O₂ I₂ Cl₂ Br₂ — "Have No Fear Of Ice-Cold Beer"

Sec 3 Pure · Topic 5 · Formulae & Equations

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6

Acids & Bases

Part A · pH, indicators, reactions, oxides

BIG IDEAAcid gives H⁺. Alkali gives OH⁻. Together: H⁺ + OH⁻ → H₂O (neutralisation).

01234567891011121314

◀ very ACIDICslightly acidicNEUTRAL 7slightly alkalinevery ALKALINE ▶

Indicator	Acid	Neutral	Alkali
Universal ⭐	red	green	violet
Methyl orange titrations (practical)	red	orange	yellow
Thymolphthalein titrations (practical)	colourless	colourless	blue
Litmus gas tests	red	—	blue

	🍋 Acid	🧼 Alkali
Ion in water	H⁺	OH⁻
pH	< 7	> 7
Examples	HCl, H₂SO₄, HNO₃, ethanoic	NaOH, KOH, NH₃(aq)
Note	alkali = a base that dissolves in water

Acid reactions — the big 3

🔩 + METAL

salt + hydrogen
fizzing; gas pops with lighted splint
Zn + H₂SO₄ → ZnSO₄ + H₂

🪨 + CARBONATE

salt + water + CO₂
fizzing; gas turns limewater milky
CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂

🧼 + BASE / ALKALI

salt + water
temperature rises (exothermic)
CuO + H₂SO₄ → CuSO₄ + H₂O

HCl → chlorideH₂SO₄ → sulfateHNO₃ → nitrate

Strong vs weak · concentrated vs dilute

💪STRONG / WEAK

= how much it ionises in water
strong: HCl, H₂SO₄, HNO₃ · weak: ethanoic, citric, carbonic

💧CONC / DILUTE

= how much acid per volume of water

✍ WRITE THIS"A weak acid partially ionises in water, so it has a lower concentration of H⁺ ions than a strong acid of the same concentration."

Bases — 2 more reactions

🧪 BASE + AMMONIUM SALT

salt + water + ammonia (warm)
gas turns damp red litmus blue
NaOH + NH₄Cl → NaCl + H₂O + NH₃

🌱 ACIDIC SOIL

crops grow badly in soil that's too acidic
→ add calcium hydroxide (slaked lime) to neutralise it

✍ WRITE THIS"Acids produce H⁺ ions in water. Alkalis produce OH⁻ ions. A neutral solution has equal concentrations of H⁺ and OH⁻. The higher the H⁺ concentration, the lower the pH."

Types of oxides

ACIDIC

non-metal oxides
CO₂, SO₂, NO₂
react with bases

BASIC

metal oxides
CuO, MgO, CaO
react with acids

AMPHOTERIC

react with both
Al₂O₃, ZnO
"Al-Zn"

NEUTRAL

react with neither
CO, NO, H₂O

Sec 3 Pure · Topic 6 · Acids & Bases

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6

Salts

Part B · Solubility rules & making salts

BIG IDEAFirst ask: is the salt soluble? That decides the method.

Solubility rules

Salt type	✅ Soluble	❌ Insoluble (exceptions)
Na⁺, K⁺, NH₄⁺ salts	ALL	none
Nitrates	ALL	none
Chlorides	most	AgCl, PbCl₂
Sulfates	most	BaSO₄, PbSO₄, CaSO₄
Carbonates	only Na⁺, K⁺, NH₄⁺	all others
Hydroxides / oxides	only Na⁺, K⁺, (Ca²⁺ slightly)	all others

🧠 HOOK"SNAP" always soluble: Sodium, Nitrate, Ammonium, Potassium. Insoluble chlorides: Ag, Pb. Insoluble sulfates: Ba, Pb, Ca.

Which method?

① EXCESS SOLID

e.g. CuSO₄ from CuO
1. add excess CuO to warm acid, stir
2. filter off unreacted solid
3. heat filtrate to saturation
4. cool → crystals, filter, wash, dry

② TITRATION

e.g. NaCl from NaOH + HCl
1. titrate with indicator → find volume
2. repeat without indicator using same volumes
3. evaporate to saturation
4. cool → crystals

③ PRECIPITATION

e.g. BaSO₄
1. mix the 2 solutions
2. filter → salt is the residue
3. wash with distilled water
4. dry between filter papers

⚠ TRAPWhy excess solid? To make sure all the acid is used up. Why repeat without indicator? So the salt is not contaminated.

Sec 3 Pure · Topic 6 · Salts

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7

Identifying Ions & Gases

Qualitative analysis (QA)

BIG IDEAAdd a reagent → watch the colour / gas → name the ion. Always check "in excess".

Cations — add NaOH(aq), then NH₃(aq)

Ion	NaOH — few drops	NaOH — excess	NH₃ — few drops	NH₃ — excess
Cu²⁺	light blue ppt	insoluble	light blue ppt	dark blue solution
Fe²⁺	green ppt	insoluble	green ppt	insoluble
Fe³⁺	red-brown ppt	insoluble	red-brown ppt	insoluble
Zn²⁺	white ppt	dissolves → colourless	white ppt	dissolves → colourless
Al³⁺	white ppt	dissolves → colourless	white ppt	insoluble
Ca²⁺	white ppt	insoluble	no ppt
NH₄⁺	no ppt · warm → NH₃ gas (damp red litmus → blue)		—

🧠 HOOKColoured ppt = Cu (blue), Fe²⁺ (green), Fe³⁺ (brown). White + dissolves in both excesses = Zn²⁺ only.

⚠ TRAPThe exam data sheet gives the ppt colours — the marks are for the "excess" columns. Al³⁺ vs Zn²⁺: only Zn dissolves in excess NH₃.

Anions

Ion	Test	Positive result
CO₃²⁻	add dilute acid	effervescence — CO₂ gives white ppt with limewater
Cl⁻	acidify (dil. HNO₃) + AgNO₃(aq)	white ppt (AgCl)
I⁻	acidify (dil. HNO₃) + AgNO₃(aq)	yellow ppt (AgI)
SO₄²⁻	acidify (dil. HNO₃) + Ba(NO₃)₂(aq)	white ppt (BaSO₄)
NO₃⁻	NaOH(aq) + aluminium foil, warm	NH₃ gas — damp red litmus → blue

⚠ TRAPWhy acidify with dilute nitric acid? To remove carbonate ions, which would also give a white ppt. Don't use HCl (adds Cl⁻) or H₂SO₄ (adds SO₄²⁻).

Gas tests

💥 H₂

lighted (burning) splint → "pop"

🔥 O₂

glowing splint relights

🥛 CO₂

limewater → white ppt (dissolves in excess CO₂)

🔵 NH₃

damp red litmus → blue

🧻 Cl₂

damp litmus paper is bleached

🟣 SO₂

acidified KMnO₄ purple → colourless

Sec 3 Pure · Topic 7 · Identifying Ions & Gases

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8

Chemical Calculations

Part A · The mole map & formulas

BIG IDEAEverything goes through MOLES. Convert to moles → use the ratio → convert back.

green = INTO moles · red = OUT of moles

The formula cards

Moles from mass

n = m ÷ Mᵣ

Moles of gas

n = V ÷ 24
V in dm³ at r.t.p.

Concentration

c = n ÷ V
mol/dm³ · V in dm³

Particles

N = n × 6.02×10²³
6.02×10²³ = Avogadro constant

g/dm³ ⇄ mol/dm³

g/dm³ = mol/dm³ × Mᵣ

% yield

actual ÷ theoretical × 100

% purity

pure mass ÷ sample mass × 100

% of element

(no. × A_r) ÷ Mᵣ × 100

Working out Mᵣ

H₂SO₄ = 2(1)+32+4(16) = 98
add up all the A_r

Every mole question — 4 steps

Balanced equation

What you know → moles

× mole ratio (big numbers)

Moles → unit asked

⚠ TRAPcm³ ÷ 1000 = dm³ before using V. (250 cm³ = 0.25 dm³)

⚠ TRAPThe ratio works on moles, never on grams.

Sec 3 Pure · Topic 8 · Chemical Calculations

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8

Chemical Calculations

Part B · Worked examples (copy the layout)

① Reacting masses

Mass of Fe from 16 g Fe₂O₃?
Fe₂O₃ + 3CO → 2Fe + 3CO₂

n(Fe₂O₃)	16 ÷ 160 = 0.1
ratio 1 : 2	n(Fe) = 0.2
mass	0.2 × 56 = 11.2 g

② Gas volume

Volume of CO₂ from 10 g CaCO₃?
CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂

n(CaCO₃)	10 ÷ 100 = 0.1
ratio 1 : 1	n(CO₂) = 0.1
volume	0.1 × 24 = 2.4 dm³

③ Concentration

4 g NaOH (Mᵣ 40) in 250 cm³

n	4 ÷ 40 = 0.1 mol
V	250 ÷ 1000 = 0.25 dm³
c	0.1 ÷ 0.25 = 0.4 mol/dm³

④ Titration

25.0 cm³ NaOH needs 20.0 cm³ of 0.10 mol/dm³ HCl. c(NaOH)?

n(HCl)	0.10 × 0.0200 = 0.00200
ratio 1 : 1	n(NaOH) = 0.00200
c	0.00200 ÷ 0.0250 = 0.080 mol/dm³

Repeat until results are concordant (within 0.10 cm³)

⑤ Concentration in g/dm³

0.4 mol/dm³ NaOH (Mᵣ 40) in g/dm³?
0.4 × 40 = 16 g/dm³

20 g/dm³ NaOH in mol/dm³?
20 ÷ 40 = 0.5 mol/dm³

⑥ Empirical formula — use a table

	C	H	O
% (or g)	40.0	6.7	53.3
÷ A_r	40.0 ÷ 12 = 3.33	6.7 ÷ 1 = 6.7	53.3 ÷ 16 = 3.33
÷ smallest	1	2	1
Formula	CH₂O

Molecular formula

If Mᵣ = 180:
CH₂O mass = 30
180 ÷ 30 = 6
→ C₆H₁₂O₆

⑦ Limiting reactant

4 g H₂ + 40 g O₂ → water. 2H₂ + O₂ → 2H₂O
n(H₂) = 4 ÷ 2 = 2 · n(O₂) = 40 ÷ 32 = 1.25
2 mol H₂ needs only 1 mol O₂ → O₂ is in excess
→ H₂ is limiting · water = 2 mol = 36 g

🧠 HOOKThe limiting reactant runs out first. Always calculate the product from it.

⑧ % yield & purity

Expected 11.2 g Fe, got 8.4 g
8.4 ÷ 11.2 × 100 = 75% yield

20 g sample has 18 g pure CaCO₃
18 ÷ 20 × 100 = 90% pure

% N in NH₄NO₃ (Mᵣ 80)
28 ÷ 80 × 100 = 35% by mass

✍ EXAM TIPShow every line: formula → numbers → answer + unit. Give answers to 3 significant figures unless told otherwise.

Sec 3 Pure · Topic 8 · Chemical Calculations

🗺️

9

The Periodic Table

Groups, periods & trends

BIG IDEASame group = same number of outer electrons = similar reactions.

GROUP 1 · Alkali metals 🔥

1 outer e⁻ → forms +1 ionssoft, low densitystored under oil

Li
Na
K

⬇

more reactive
lower melting point
(outer e⁻ further away, lost more easily)

2Na + 2H₂O → 2NaOH + H₂
fizzes, moves on water, forms an alkali — K most violent

GROUP 17 · Halogens 🧪

Cl₂	yellow-green gas
Br₂	red-brown liquid
I₂	black solid (purple vapour)

⬇ down group: less reactive, darker, higher m.p.

Halogen displacement

add ↓ to →	KCl	KBr	KI
Cl₂	—	✓ orange	✓ brown
Br₂	✗	—	✓ brown
I₂	✗	✗	—

Cl₂ + 2KBr → 2KCl + Br₂
ionic: Cl₂ + 2Br⁻ → 2Cl⁻ + Br₂

🧠 HOOKA more reactive halogen pushes a less reactive one out of its salt. Cl beats Br beats I — "higher up wins".

🔮 Predict it (exam favourite)

Rubidium (below K) → even more reactive, lower m.p.
Astatine (below I) → darker, solid, least reactive halogen
1–3 outer e⁻ → metal · 5–7 outer e⁻ → non-metal

⚙️ Transition elements

high m.p.high densityvariable oxidation statescoloured compoundscatalysts (Fe in Haber process)

💤 Group 18 · Noble gases

full outer shell (stable) → no need to lose, gain or share electrons → unreactive
monoatomic (single atoms)
Ar, Ne — light bulbsHe — balloonsAr — making steel

Sec 3 Pure · Topic 9 · The Periodic Table

✏️

✎

Practical & Drawing Skills

How to draw it · how to do it · how to write it

BIG IDEAMarks come from exact steps and exact words, not long answers.

How to draw dot-and-cross — step by step

⚡ IONIC (e.g. MgCl₂)

① Work out the ratio from charges (Mg²⁺ needs 2 Cl⁻)
② Metal ion: draw its full outer shell (8) or leave it empty
③ Non-metal ion: 8 electrons — the gained ones as the other symbol
④ [ brackets ] + charge on every ion

🤝 COVALENT (e.g. H₂O)

① Count each atom's outer electrons (O = 6, H = 1)
② How many more does each need? (O needs 2, H needs 1)
③ Overlap circles · put each shared pair (1 • + 1 ×) in the overlap
④ Add leftover electrons as pairs · check O = 8, H = 2

How to draw apparatus

✂️ draw a 2-D side view (cross-section)

🏷️ label every piece of apparatus

🚫 no gaps where gas could escape — stopper the flask

🔥 show heat with an arrow · draw liquid levels

Titration — method (Paper 5 favourite)

Rinse burette with the acid, fill it, record the initial reading

Pipette 25.0 cm³ of alkali into a conical flask · add 2–3 drops methyl orange

Add acid while swirling · stop at the first permanent colour change (yellow → orange)

Record final reading · repeat until 2 results are concordant (within 0.10 cm³) · average them

🧠 READING THE BURETTEEye level with the bottom of the meniscus. Record to 2 decimal places, ending in 0 or 5 (e.g. 23.45 cm³). Volume used = final − initial.

Getting crystals from a solution

Heat to evaporate some water until saturated

Cool slowly — crystals form

Filter to collect the crystals

Wash with a little cold distilled water, dry between filter papers

How to write QA observations

✍ COPY THIS STYLE"white ppt, soluble in excess giving a colourless solution"
"effervescence; gas gave a white ppt with limewater"

⚠ TRAPWrite what you SEE, not the name. ✗ "CO₂ given off" → ✓ "effervescence, gas turns limewater milky". Always state the colour + "in excess" result.

What the question word wants

Word	Give…	Word	Give…
State / Name	short answer, no reason	Suggest	apply ideas to a new situation
Describe	what happens / what you see	Deduce	conclusion from the given data
Explain	the reason why — use "because…, so…"	Predict	the likely result, using a trend
Define	the word-perfect definition	Calculate	working + answer + unit

🧪 PAPER 5 EXTENSION"Suggest a modification": repeat & average · use a burette/pipette instead of a measuring cylinder · use a gas syringe to measure gas · control temperature.

Sec 3 Pure · Practical & Drawing Skills

🎨

★

Quick-ID: Flowchart & Colours

Unknown cation? Follow the arrows

⬇ PRECIPITATES (solids that form)

Cu(OH)₂light blue

Fe(OH)₂green

Fe(OH)₃red-brown

Zn, Al, Ca hydroxideswhite

AgClwhite

BaSO₄white

AgIyellow

CaCO₃white (milky limewater)

💧 SOLUTIONS

Cu²⁺(aq)blue

Cu²⁺ + excess NH₃dark blue

Fe²⁺(aq)pale green

Fe³⁺(aq)yellow-brown

Br₂(aq)orange

I₂(aq)brown

KMnO₄(aq)purple

Zn²⁺, Al³⁺, Ca²⁺ (aq)colourless

🧱 ELEMENTS

Cl₂yellow-green gas

Br₂red-brown liquid

I₂black solid, purple vapour

Trend ⬇colour gets darker

🔁 COLOUR-CHANGE TESTS

Limewater — CO₂colourless → milky white

Acidified KMnO₄ — SO₂purple → colourless

Damp red litmus — NH₃red → blue

Damp blue litmus — Cl₂blue → red → bleached

🧪 INDICATORS

Indicator	Acid	Neutral	Alkali
Litmus	red	—	blue
Methyl orange	red	orange	yellow
Universal indicator	red	green	violet

Sec 3 Pure · Quick-ID & Colours

📖

★

Definitions — Word Perfect

The yellow words are where the marks are

Term	Definition
🔬 MATTER
Element	a substance made of only one type of atom
Compound	two or more elements chemically combined in a fixed ratio
Mixture	two or more substances not chemically combined
⚛️ ATOMS & BONDS
Proton number	number of protons in the nucleus of an atom
Nucleon (mass) number	total number of protons and neutrons in the nucleus
Isotopes	atoms of the same element with the same number of protons but different numbers of neutrons
Relative atomic mass (A_r)	average mass of an atom compared with 1/12 the mass of a carbon-12 atom
Diffusion	net movement of particles from a higher to a lower concentration
Ion	a charged particle formed when an atom loses or gains electrons
Ionic bond	strong electrostatic attraction between oppositely charged ions
Covalent bond	a shared pair of electrons between two atoms
Metallic bond	attraction between positive metal ions and a sea of delocalised electrons
Alloy	a mixture of a metal with one or more other elements
🍋 ACIDS & BASES
Acid	a substance that produces H⁺ ions when dissolved in water
Base	a substance that reacts with an acid to form a salt and water only
Alkali	a soluble base that produces OH⁻ ions in water
Neutral	a solution with equal concentrations of H⁺ and OH⁻ (pH 7)
pH	a scale (0–14) of acidity / alkalinity; lower pH = more H⁺
Strong acid	an acid that completely ionises in water
Weak acid	an acid that partially ionises in water
Salt	formed when the H⁺ of an acid is replaced by a metal ion or NH₄⁺
Neutralisation	reaction of an acid with a base to form salt and water (H⁺ + OH⁻ → H₂O)
Amphoteric oxide	an oxide that reacts with both acids and bases
🧮 MOLES
Relative molecular / formula mass (Mᵣ)	sum of the relative atomic masses of all the atoms in the formula
Mole	amount of substance containing 6.02 × 10²³ particles
Molar volume	1 mole of any gas occupies 24 dm³ at r.t.p.
Empirical formula	the simplest whole-number ratio of atoms in a compound
Molecular formula	the actual number of each type of atom in one molecule
Concentration	amount of solute in 1 dm³ of solution (mol/dm³ or g/dm³)
Limiting reactant	the reactant that is used up first and decides how much product forms

🧠 TEST YOURSELFCover the right column. Say each definition out loud. Only the yellow words need to be exact.

Sec 3 Pure · Definitions

Sec 3 Pure ChemVisual Notes

Experimental Chemistry

Which method? Just match the mixture

The 3 diagrams you must draw

Experimental Chemistry

Measuring volume — accuracy ladder

Collecting gases — 3 ways

Drying gases

Is it pure?

Kinetic Particle Theory

Changes of state

Heating curve

Diffusion

Atomic Structure

Electron shells fill 2 → 8 → 8

Count protons, neutrons, electrons — atoms and ions

Isotopes

Chemical Bonding

Structure → properties (the big table)

Alloys — why they're harder

Chemical Bonding

Ionic

Covalent — the 5 syllabus molecules (+1 practice)

Element · compound · mixture

Chemical Bonding

Diamond vs graphite (both pure carbon)

Silicon dioxide (SiO₂, sand)

Compare the 3 covalent structures

Metallic bonding

Formulae & Equations

Ion bank — memorise these

Writing a formula — swap & drop

Balancing an equation — 4 steps

Ionic equations — 3 steps

Acids & Bases

Acid reactions — the big 3

Strong vs weak · concentrated vs dilute

Bases — 2 more reactions

Types of oxides

Salts

Solubility rules

Which method?

Identifying Ions & Gases

Cations — add NaOH(aq), then NH₃(aq)

Anions

Gas tests

Chemical Calculations

The formula cards

Every mole question — 4 steps

Chemical Calculations

⑤ Concentration in g/dm³

⑥ Empirical formula — use a table

⑦ Limiting reactant

⑧ % yield & purity

The Periodic Table

Halogen displacement

Practical & Drawing Skills

How to draw dot-and-cross — step by step

How to draw apparatus

Titration — method (Paper 5 favourite)

Getting crystals from a solution

How to write QA observations

What the question word wants

Quick-ID: Flowchart & Colours

Definitions — Word Perfect

Sec 3 Pure Chem
Visual Notes