IP Combined Science Notes (Lower Sec, Year 1-2): 03) Elements, Compounds, Mixtures & Separation
Download printable cheat-sheet (CC-BY 4.0)08 Dec 2025, 00:00 Z
A clear view of particle composition lets you justify why certain apparatus combinations purify substances while others fail.
Learning targets
- Classify matter using particle diagrams, chemical symbols, and formulae.
- Write simple word and chemical equations with state symbols.
- Select separation techniques suited to mixtures (solid-solid, solid-liquid, liquid-liquid).
- Explain purification steps with annotated apparatus diagrams.
1. Matter classification
| Type | Definition | Example | Particle view |
| Element | Substance made of one type of atom. | \( \ce{O2} \), \( \ce{Cu} \). | Identical spheres. |
| Compound | Substance formed by chemically bonded atoms of different elements. | \( \ce{H2O} \), \( \ce{NaCl} \). | Repeating units with fixed ratio. |
| Mixture | Physical combination of substances, no fixed ratio. | Air, seawater. | Different particles interspersed without bonding. |
Chemical equations must conserve atoms. Example combustion:
\[ \ce{CH4 + 2O2 -> CO2 + 2H2O}. \]
2. Separation techniques overview
| Mixture type | Goal | Technique | Key idea |
| Insoluble solid + liquid | Remove solid | Filtration | Filter paper traps residue; filtrate passes through. |
| Dissolved solid + liquid | Obtain solute | Evaporation to dryness | Heat to remove solvent; stop before spattering. |
| Dissolved solid + liquid | Obtain solute (without decomposition) | Crystallisation | Heat to concentrate, cool to form crystals. |
| Miscible liquids | Separate components by boiling point | Fractional distillation | Column allows vapours to condense separately. |
| Soluble solids with different solubilities | Separate pigments | Paper chromatography | Different affinities for mobile/stationary phases. |
Worked example — Separating ink from water
- Use simple distillation: heat solution; water vaporises first.
- Vapour condenses in Liebig condenser and collects as distillate.
- Ink dyes remain in distillation flask because boiling points are higher.
Sketch apparatus with labels: heat source, thermometer at still head, condenser with water-in at lower end, water-out at upper end.
3. Purification checks
- Melting/boiling point consistency: Pure substances have sharp transitions; impurities broaden the range.
- Chromatography \( R_f \): \( R_f = \frac{\text{distance travelled by substance}}{\text{distance travelled by solvent}} \). Values closer to 1 mean higher solubility in mobile phase.
Sample calculation
If a dye spot travels \( \pu{4.8 cm} \) while solvent front travels \( \pu{6.0 cm} \):
\[ R_f = \frac{4.8}{6.0} = 0.80. \]
Compare against reference values to identify pigments.
4. Safety & good practice
- Clamp apparatus securely when heating.
- Use boiling chips to prevent bumping during distillation.
- Position thermometer bulb at the level of the side arm to measure vapour temperature accurately.
Try it yourself
- Classify each sample as element, compound, or mixture: brass, dry ice, graphite.
- Outline how to obtain pure copper(II) sulfate crystals from its aqueous solution. Include cooling step rationale.
- In chromatography, pigment A has \( R_f = 0.52 \) and pigment B has \( R_f = 0.65 \). The solvent front is \( \pu{7.5 cm} \). How far did each pigment travel? Explain which has higher affinity for the stationary phase.
Advance to cell biology at https://eclatinstitute.sg/blog/ip-combined-sciences-lower-sec-notes/IP-Combined-Science-Lower-Sec-04-Cells-Diffusion-and-Organisation.
