⚗️ IGCSE Chemistry · S1 In‑Depth · Mid‑Year

📘 Core topics · Theory + practical ⏳ 2h exam · 100 level 🧪 Section A · B · C

✅ Exam review checklist: topics students should revise

Use this list before working through the questions. Students should be able to explain the ideas, interpret diagrams, complete calculations, and apply practical skills.

1. Particles and states of matter
  • Solid, liquid and gas particle arrangements
  • Changes of state: melting, freezing, boiling and condensing
  • Heating and cooling curves, including plateaus and latent heat
2. Diffusion and dissolving
  • Diffusion as random movement from high to low concentration
  • Effect of temperature and particle mass on diffusion rate
  • Difference between dissolving, diffusion and chemical reaction
3. Separation techniques
  • Filtration, evaporation, crystallisation and simple distillation
  • Fractional distillation of miscible liquids with different boiling points
  • Choosing the correct method for mixtures
4. Chromatography and purity
  • Solvent front, baseline/origin and spots
  • Pure substance = one spot; mixture = multiple spots
  • Rf value = distance moved by spot ÷ distance moved by solvent
  • Pure substances have sharp melting/boiling points
5. Atomic structure and isotopes
  • Protons, neutrons and electrons: charge, mass and location
  • Atomic/proton number and mass/nucleon number
  • Isotopes and weighted average relative atomic mass
6. Periodic table
  • Groups, periods and valence electrons
  • Group I, Group VII and Group 0 trends/properties
  • Transition metals and identifying elements from proton number
7. Bonding and structure
  • Ionic bonding by electron transfer
  • Metal and non-metal ion charges
  • Simple molecular, ionic and metallic properties
  • Diatomic elements such as Cl₂ and Br₂
8. Practical and apparatus skills
  • Correct use of burette, pipette, measuring cylinder, thermometer and gas syringe
  • Collecting and measuring gas volumes
  • Hydrated salts, water of crystallisation and mass-loss calculations
  • Graph plotting and interpreting experimental data
📌 Section A · Multiple Choice (varied) with detailed notes

🔹 Diffusion & random motion

MCQ

Which statement about diffusion is correct?

✔ B — diffusion is the net movement of particles from high to low concentration, driven by random motion.
📘 In-depth: Diffusion occurs in gases and liquids. Temperature increases kinetic energy → faster diffusion. Small molecules (e.g., O₂, CO₂) can cross cell membranes via diffusion. Cell walls are fully permeable, not a barrier.

🔹 Particle arrangement · solution & gas

MCQ
Particle diagrams: solution compared with gas
Solution solute particles evenly spread among solvent Gas particles far apart; random motion
Use this visual for Q2 and Q3: a solution is mixed but still close together; a gas has widely spaced particles.

Which diagram shows the particles in a solution?

✔ B — solute particles are spread evenly between solvent molecules.
📘 In-depth: In a solution, the solute dissolves and particles are interspersed. In a gas (C), particles are far apart and move freely. Solids (D) vibrate in fixed positions.

Which represents particles in a gas?

✔ C — gas particles have negligible forces, move randomly and fill container.

🔹 Dissolving & diffusion

MCQ

A purple crystal is placed in water. What happens?

✔ D — no chemical reaction; the crystal dissolves and the ions/molecules diffuse.
📘 In-depth: Dissolving is physical (intermolecular forces break). Diffusion spreads the coloured particles. No new substance is formed.

🔹 Diffusion rate · molar mass

MCQ

Why does neon diffuse faster than CO₂?

✔ A — lighter particles move faster (Graham's law: rate ∝ 1/√molar mass).
📘 In-depth: Ne (20) vs CO₂ (44). At same temperature, lighter Ne has higher average speed. Noble gas character (C) is not the reason.

🔹 Chromatography · purity

MCQ
Chromatogram for purity: single spot = pure
solvent frontbaseline WXYZ
W and Y each have one spot, so they are pure. X and Z have more than one spot, so they are mixtures.

In a chromatogram, which spots indicate pure substances?

✔ B — single spots (W and Y) indicate a single component → pure.
📘 In-depth: Multiple spots = mixture. Rf values can be used to identify compounds. Pure substances give one spot under given conditions.

🔹 Purity & boiling point

MCQ

Which property shows a liquid is pure?

✔ D — a pure substance has a sharp, constant boiling point (or melting point).
📘 In-depth: Impurities lower melting point and raise boiling point (boiling point range). A, B, C are not definitive.

🔹 Separation · boiling points

MCQ
Fractional distillation apparatus
ethanol + water fractionating column condenser water outwater in distillate heat
The lower boiling liquid vaporises first, passes through the condenser, and is collected as the distillate.

Two liquids with BP 120°C and 160°C. Which apparatus separates them?

✔ A — fractional distillation separates liquids with different boiling points.
📘 In-depth: Fractionating column allows repeated condensation/vaporisation. The more volatile (lower BP) distils first.

🔹 Phase changes

MCQ
Phase-change map
SOLIDLIQUIDGASmeltingfreezingboilingcondensing

Identify W, X, Y, Z in the phase transition diagram.

✔ C — melting (solid→liquid), boiling (liquid→gas), freezing (liquid→solid), condensing (gas→liquid).
📘 In-depth: Energy is absorbed during melting/boiling, released during freezing/condensing. Temperature remains constant during a phase change.

🔹 Distillation · pure water

MCQ

Which method obtains pure water from aqueous potassium chloride?

✔ C — distillation boils water and condenses pure water, leaving KCl behind.
📘 In-depth: Filtration separates insoluble solids; crystallisation recovers soluble solids. Distillation is for separating a volatile liquid from non‑volatile solute.

🔹 Atomic structure · identify element

MCQ

An atom has 6 protons, 6 neutrons, 6 electrons. Which element?

✔ B — atomic number = 6 → carbon.
📘 In-depth: Proton number defines the element. Neutrons affect mass (isotopes). Electrons equal protons in neutral atom.

🔹 Isotopes · neutrons

MCQ

⁶⁴₂₉Cu and ⁶⁵₃₀Zn have the same:

✔ C — both have 35 neutrons (64−29=35; 65−30=35).
📘 In-depth: Isotopes of an element have same protons, different neutrons. Different elements can have same neutron number (isobars).

🔹 Periodic table · groups

MCQ
Mini periodic table: same column = similar properties
VWYXZW and Y are in the same group, so they have similar chemical properties.

Which two elements have similar chemical properties?

✔ C — elements in the same group have same outer shell electrons → similar properties.
📘 In-depth: Groups are vertical columns. Chemical properties are determined by valence electrons.

🔹 Isotopes · proton/neutron

MCQ
Isotope diagrams: same protons, different neutrons
12342p, 1n3p, 1n2p, 2n3p, 2nyellow = proton; blue = neutron

Which two diagrams show atoms that are isotopes?

✔ B — isotopes have same proton number but different neutron number.
📘 In-depth: Look at the nucleus: same protons, different neutrons. Example: ¹²C and ¹⁴C.

🔹 Diatomic elements

MCQ

Which elements exist as diatomic molecules?

✔ B — bromine (Br₂) and chlorine (Cl₂) are diatomic.
📘 In-depth: Diatomic elements: H₂, N₂, O₂, F₂, Cl₂, Br₂, I₂ (and At₂). Metals are monatomic.

🔹 Noble gases · full shell

MCQ

Why are noble gases unreactive?

✔ A — full outer shell (octet / duet) gives maximum stability.
📘 In-depth: Helium has 2, others have 8 valence electrons. They have very high ionisation energies.

🔹 Subatomic particles

MCQ

Which statement is correct?

✔ B — protons and neutrons are ≈1836 times heavier than electrons; neutrons are neutral.
📘 In-depth: Proton (+1), electron (–1), neutron (0). Mass: proton ≈ neutron ≈ 1 amu; electron ≈ 1/1840 amu.

🔹 Properties · metals

MCQ

Which substance is a solid metal at room temperature?

✔ B — sodium (mp 98°C) is a solid metal at RT, conducts in both states (metallic bonding).
📘 In-depth: Metals conduct electricity in solid and liquid state due to delocalised electrons. Non‑metals typically don't conduct.

🔹 Ion charges

MCQ

What charges do metal and non‑metal ions form?

✔ C — metals lose electrons → positive (cations); non‑metals gain electrons → negative (anions).
📘 In-depth: Metals have low electronegativity, tend to form cations. Non‑metals have high electronegativity, form anions.

🔹 Ionic bonding · electron transfer

MCQ
Ionic bonding: W transfers one electron to X
W2,1X2,7electron transferW⁺ cationX⁻ anion

Electronic structures: W (2.1), X (2.7), Y (2.8.4), Z (2.8.8). Which pair forms an ionic compound?

✔ A — W (metal, 1 valence e⁻) and X (non‑metal, 7 valence e⁻) → ionic by electron transfer.
📘 In-depth: Ionic bonds form between metals (low IE) and non‑metals (high EA). W (Li/Na) and X (F/Cl) will form ionic compound.

🔹 Apparatus · titration

MCQ
Titration apparatus: burette delivers measured volume
burette scale / cm³conical flaskburette

Which statement about apparatus is correct?

✔ A — burette delivers variable volumes accurately in titrations.
📘 In-depth: Pipette measures fixed volume (e.g., 25 cm³). Measuring cylinder measures approximate volume. Thermometer measures temperature.

🔹 Periodic table · group from Z

MCQ

Element X has nucleon number 27, proton number 13. Which group?

✔ B — Z=13 → aluminium, group 13 (III).
📘 In-depth: Group number = number of valence electrons for main group elements. Al has 3 valence electrons.
📘 Section B · Structured (varied) with supporting notes

🧂 Separation & distillation

structured
Separation sequence: sand + salt
sand + saltadd watersalt solution+ sandfiltersand residueevaporate filtratesalt crystals

a) Particle arrangement in a solid:

Arrangement: regular, closely packed lattice (fixed positions).
Movement: particles vibrate about fixed points; strong intermolecular forces.

b) Separate sand from salt:

Add water → salt dissolves (soluble), sand does not (insoluble). Filter → sand on filter paper. Evaporate filtrate to obtain salt crystals.

c) Fractional distillation of ethanol/water:

Fractional distillation is used. The top of the column is cooler than the bottom. The more volatile (ethanol, bp 78°C) vaporises and moves up, then condenses in the condenser to liquid.
📘 Supporting notes: Fractional distillation relies on different boiling points. Ethanol (78°C) and water (100°C). A fractionating column provides temperature gradient. More volatile component distils first.

❄️ Cooling curve & states

structured
Cooling curve: plateaus show changes of state
timetemperature / °Ccondensing / boiling pointfreezing / melting pointplateauplateau

a) State at 23°C for substance with mp –15°C, bp 78°C: liquid (between mp and bp).

b) Temperature during change of state: remains constant (latent heat).

c) Melting point from curve: 70°C (plateau).

d) Not water: melting/boiling points differ from 0°C / 100°C.

e) Substance: sodium (mp 98°C, bp 890°C) – based on data.

f) Cooling curve for water: plateau at 100°C (condensation) and 0°C (freezing).

📘 Supporting notes: A cooling curve shows temperature vs time. During phase transitions, energy is released without temperature change. Pure substances have sharp melting/boiling points.

⚛️ Isotopes · average atomic mass

calculation

Lead isotopes: ²⁰⁴Pb (1.37%), ²⁰⁶Pb (26.26%), ²⁰⁷Pb (20.82%), ²⁰⁸Pb (51.55%).

Mass numbers: 204, 206, 207, 208.
Average atomic mass = (204×0.0137) + (206×0.2626) + (207×0.2082) + (208×0.5155) = 207.2 (approx).
📘 Supporting notes: Relative atomic mass is weighted average of isotope masses. Abundance is percent divided by 100.

🧪 Bonding & properties

structured

a) Three differences solid vs gas:

  • Arrangement: solid – ordered, gas – random.
  • Forces: solid – strong; gas – negligible.
  • Motion: solid – vibrate; gas – move freely at high speed.

b) Gases at 30°C: K (bp –25°C). Simple molecules: K and N (covalent molecular).

c) i) Bonding: M (solid, conducts when molten but not as a solid) – ionic; N (liquid, poor conductor) – covalent (simple molecular).

ii) Higher boiling point of M: strong ionic lattice forces need more energy to overcome.

📘 Supporting notes: Ionic compounds have high melting/boiling points due to strong electrostatic forces. Simple molecular substances have weak intermolecular forces, low boiling points.

🧪 Elements · periodic table

structured

a) Increasing proton number: Cl (17), Ar (18), K (19), Br (35), I (53)

b) Increasing relative atomic mass: Cl (35.5), K (39.1), Ar (39.9), Br (79.9), I (126.9)

c) Why orders differ: presence of neutrons (isotopes) affects mass, not proton number.

d) Same group: bromine, chlorine, iodine (Group VII)

e) i) one outer electron: potassium ; ii) full outer shell: argon ; iii) radioactive isotope: iodine-131 (thyroid treatment) or cobalt-60.

📘 Supporting notes: Atomic number = protons. Mass number = protons + neutrons. Isotopes cause differences between atomic number order and mass order. Group VII elements are halogens.

🔬 Bohrium · formula & period

structured
Periodic table positions used for Group, Period and transition-metal questions
ABCDEFGHJKLMNPQRSGroup Itransition metals / d-blockGroup VIIGroup 0Period 4 row includes Group VII element N and Group 0 element S. Group I reactivity increases downward: D is more reactive than A, B or C.
This simplified table supports the structured periodic-table questions: vertical columns are groups, horizontal rows are periods, and the central block represents transition metals.

a) i) Bohrium (Z=107). Protons = 107. Neutrons = mass number – 107.

ii) Compound with 1 Bh, 3 O, 1 Cl: BhO₃Cl.

b) i) Transition metal from letters: (choose from diagram).
ii) Group VII, period 4: (letter).
iii) More reactive Group I: lower down the group.
iv) Same group: letters.

📘 Supporting notes: Transition metals are in the d‑block. Reactivity in Group I increases down the group (larger atomic radius, lower ionisation energy).
🔬 Section C · Alternative to practical (varied)

📈 Heating curve

practical
Heating curve guide
time / mintemperature / °C70°C melting plateaumeltingliquid warms

Data: temperature vs time (0–60 min). Plot graph. Melting point = 70°C (plateau). Boiling point not reached (above 90°C). After 50 min: particles gain kinetic energy, temperature rises.

📘 Supporting notes: During melting, temperature is constant as energy is used to overcome intermolecular forces. After melting, temperature rises again.

🧪 Hydrated copper sulphate

practical
Hydrated copper(II) sulfate: heating removes water of crystallisation
blue hydratedCuSO₄·5H₂Oheatwater driven offwhite anhydrousCuSO₄mass lost = mass of water removed

a) Colour: blue (CuSO₄·5H₂O).

b) Mass crystals = 9.01 – 5.97 = 3.04 g.

c) i) Mass after heating = 7.66 – 5.97 = 1.69 g (anhydrous).
ii) Water lost = 3.04 – 1.69 = 1.35 g.

📘 Supporting notes: Heating drives off water of crystallisation. The white anhydrous CuSO₄ is formed. Mass loss = water.

📏 Apparatus & gas volume

practical
Measuring gas with a gas syringe
020406080gas syringe / cm³reaction flask

a) Apparatus: gas syringe (or measuring cylinder over water).

b) Volume of gas: read from scale (e.g., 45 cm³).

📘 Supporting notes: Gas syringes are used to collect and measure gas volumes. Calibrated in cm³.

🎨 Chromatography · sweets

practical
Paper chromatography: baseline, solvent front and separated dyes
solvent frontbaseline / originCDtwo spots = mixtureone spot = pure dye
The starting spots must be on the baseline above the solvent. The solvent front is marked before the paper dries.

a) Process: paper chromatography.

b) Solvent: water (dyes are water‑soluble).

c) i) Line A: solvent front ; ii) Line B: baseline / origin.

d) Conclusions: Sweet C has 2 colours (mixture), sweet D has 1 colour (pure dye) – based on spots.

📘 Supporting notes: Rf = distance moved by spot / distance moved by solvent. Each dye has characteristic Rf. Multiple spots = mixture.
⚡ Interactive study guide · in‑depth notes for every topic ·