IMAT Chemistry · Free notes
Solutions: Solubility, Concentration and Dilution
Solutions and Concentration has 16 past questions since 2011, and the ministry papers from 2023 on have asked 2 of them. Both ministry questions were short calculations: how much water dilutes a solution to a lower concentration, and how many moles of one ion are in a volume of a salt solution. The older papers mixed recall about solubility and mixtures with unit conversions between grams, moles, millilitres and litres. Most mistakes here are a missing factor: millilitres left unconverted, a molar mass forgotten, or two ions from one formula counted as one.
The handout has every subtopic, worked example, formula and trap with answers shown. The formula sheet is the chapter’s formulas and traps alone, on one page.
Subtopic notes
Solutions, Mixtures and How to Separate Them
0 PYQsA solution is a mixture that looks the same all the way through; each kind of mixture is separated by the property its parts do not share.
Like Dissolves Like, Electrolytes and Saturation
0 PYQsA substance dissolves when its particles are attracted to the solvent's about as strongly as to each other, and only up to a limit that depends on temperature.
Molarity, Mass Concentration and Other Units
0 PYQsConcentration says how much solute is in a given amount of solution; the units differ in whether they count moles or grams, and per volume or per mass.
Preparing, Diluting, Mixing and Reacting Solutions
0 PYQsAdding water spreads the same moles of solute through more volume, and in a reaction between solutions the moles from n = cV follow the equation's ratio.
Boiling Point, Freezing Point and Osmotic Pressure
0 PYQsSome properties of a solution depend only on how many solute particles it contains, not on what they are: it boils higher, freezes lower and draws water across a membrane.
Formula & revision sheet
12 formulas · 4 reference tables · 17 gotchas across all subtopics — the exam-eve cheat-sheet
Formula & revision sheet
12 formulas · 4 reference tables · 17 gotchas across all subtopics — the exam-eve cheat-sheet
Reference tables (2)
Solutions and mixtures: the key terms6 rows
| Term | Meaning | Example |
|---|---|---|
| Solution | Homogeneous mixture; particles too small to see or settle | Sugar dissolved in water |
| Suspension | Heterogeneous; particles large enough to settle or be filtered | Muddy water |
| Colloid | Particles about 1 to 1000 nm across; they scatter light and do not settle | Milk, fog |
| Miscible liquids | Mix completely to give one layer | Water and ethanol |
| Immiscible liquids | Separate into two layers | Hexane and water |
| Blood | Heterogeneous: cells suspended in plasma, which is itself a solution | Spinning blood separates the cells |
Separation techniques and when to use each7 rows
| Technique | Separates | Based on | Example |
|---|---|---|---|
| Filtration | Insoluble solid from a liquid | Particle size | Sand from water |
| Evaporation or crystallisation | Dissolved solid from its solution | Solvent evaporates, solid stays | Salt from sea water |
| Simple distillation | Solvent from a solution | Large difference in boiling point | Pure water from sea water |
| Fractional distillation | Miscible liquids | Close boiling points | Ethanol from water; crude oil fractions |
| Separating funnel | Immiscible liquids | Density; liquids do not mix | Oil from water |
| Chromatography | Dissolved substances in a mixture | Different attraction to the paper and the solvent | Plant pigments, ink dyes |
| Centrifugation | Suspended particles from a liquid | Density | Blood cells from plasma |
Watch out for (2)
- Homogeneous does not mean pure, and blood is not homogeneous→ Solutions and mixtures: the key terms
- Filtration cannot remove a dissolved substance→ Separation techniques and when to use each
Formulas (1)
Reference tables (2)
Like dissolves like: polar and non-polar solvents5 rows
| Solute | In water (polar) | In hexane (non-polar) | Reason |
|---|---|---|---|
| Most ionic salts (NaCl, KNO₃) | Dissolve | Do not dissolve | Water's dipoles attract the ions |
| Small polar molecules (ethanol, glucose, sucrose) | Dissolve | Dissolve poorly | Hydrogen bonds with water |
| Non-polar molecules (I₂, Br₂, oils, alkanes) | Barely dissolve | Dissolve | Only weak dispersion forces on both sides |
| Non-polar gases (O₂, N₂, H₂) | Very slightly | Slightly | Weak attractions to any solvent |
| Giant covalent solids (SiO₂, diamond) | Insoluble | Insoluble | Strong covalent network cannot be broken |
Electrolytes and non-electrolytes: which particles are in a solution4 rows
| Solute type | Particles in water | Conducts? | Examples |
|---|---|---|---|
| Strong electrolyte | Ions only, plus water molecules | Well | NaCl, HCl, KOH, MgCl₂ |
| Weak electrolyte | Mostly molecules, a few ions | Weakly | Ethanoic acid, ammonia |
| Non-electrolyte | Solute molecules and water molecules | No | Glucose, sucrose, ethanol, urea |
| Undissolved ionic solid | Ions fixed in a lattice | No | Solid sodium chloride |
Watch out for (4)
- Ionic does not always mean soluble, covalent does not always mean insoluble→ Like dissolves like: polar and non-polar solvents
- A salt solution contains ions and molecules, not atoms→ Electrolytes and non-electrolytes: which particles are in a solution
- Cooling removes solute, not solvent→ Solubility, saturation and crystals formed on cooling
- Gases dissolve less in warm water→ Solubility, saturation and crystals formed on cooling
Formulas (4)
Watch out for (4)
- Millilitres must become litres→ Molarity: moles of solute per litre of solution
- g/L and mol/L differ by the molar mass→ Mass concentration in g/L and converting it to mol/L
- Divide by the mass of solution, not of solvent→ Percentage concentrations and parts per million
- Molality uses kilograms of solvent, molarity uses litres of solution→ Molality, mole fraction and converting with density
Formulas (4)
Watch out for (4)
- Made up to 1 L is not the same as dissolved in 1 L→ Preparing a solution of known concentration
- Water added is not the final volume→ Dilution: c₁V₁ = c₂V₂
- Concentrations do not add→ Mixing two solutions of the same solute
- Check the ratio before using c₁V₁ = c₂V₂→ Reacting volumes and titration
Formulas (3)
Watch out for (3)
- Count particles, not formula units→ Colligative properties and the van 't Hoff factor
- A solution boils higher and freezes lower→ Boiling point elevation and freezing point depression
- Water moves towards the more concentrated solution→ Osmosis and osmotic pressure
PYQ weightage by concept
16 concepts · 0 PYQs — where the marks actually sit, so you know what to drill first
PYQ weightage by concept
16 concepts · 0 PYQs — where the marks actually sit, so you know what to drill first
| Concept | PYQs | Share |
|---|---|---|
| Solutions and mixtures: the key termsfoundation | — | — |
| Separation techniques and when to use eachfoundation | — | — |
| Concept | PYQs | Share |
|---|---|---|
| Like dissolves like: polar and non-polar solventsfoundation | — | — |
| Electrolytes and non-electrolytes: which particles are in a solutionfoundation | — | — |
| Solubility, saturation and crystals formed on coolingfoundation | — | — |
| Concept | PYQs | Share |
|---|---|---|
| Molarity: moles of solute per litre of solutionfoundation | — | — |
| Mass concentration in g/L and converting it to mol/Lfoundation | — | — |
| Percentage concentrations and parts per millionfoundation | — | — |
| Molality, mole fraction and converting with densityfoundation | — | — |
| Concept | PYQs | Share |
|---|---|---|
| Preparing a solution of known concentrationfoundation | — | — |
| Dilution: c₁V₁ = c₂V₂foundation | — | — |
| Mixing two solutions of the same solutefoundation | — | — |
| Reacting volumes and titrationfoundation | — | — |
| Concept | PYQs | Share |
|---|---|---|
| Colligative properties and the van 't Hoff factorfoundation | — | — |
| Boiling point elevation and freezing point depressionfoundation | — | — |
| Osmosis and osmotic pressurefoundation | — | — |