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A quick map of how the big ideas of this chapter connect together.
Exploring Mixtures and their Separation
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Homogeneous mixtures
uniform composition; also called solutions
Concentration
% m/m, % m/v, % v/v
Solubility
saturated and unsaturated solutions
Separating homogeneous mixtures
three methods
Crystallization
salt from sea water; pure copper sulfate
Distillation
acetone and water; ittar; crude oil
Paper chromatography
dyes in black ink; plant pigments
Heterogeneous mixtures
non-uniform composition
Separating funnel
immiscible liquids, different densities
Sublimation
camphor and sand
Centrifugation
blood into cells and plasma
Coagulation
alum in muddy water; paneer from milk
Suspensions, colloids, Tyndall
it all comes down to particle size
Suspension
above 1000 nm, settles, filterable
Colloid
1–1000 nm, stable, scatters light
Tyndall effect
the beam becomes visible
Why does separating mixtures matter?
Substances get mixed without forming anything new
Each one keeps its own identity
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So each one can be taken back out
Using a difference in one property
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Homogeneous mixtures use solubility, boiling point or movement on paper
Crystallization, distillation, chromatography
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Heterogeneous mixtures use density, sublimability or particle size
Separating funnel, sublimation, centrifugation, coagulation
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Sugar, salt, perfume, petrol, clean water and blood tests all reach us this way
📸 Snapshots
- A mixture is formed when two or more substances are mixed and no new substance is formed.
- A homogeneous mixture has uniform composition throughout and is also called a solution; a heterogeneous mixture does not.
- A solute dissolves in a solvent to give a solution, and their masses add up.
- Concentration is expressed as % m/m, % m/v or % v/v, and the denominator is always the solution.
- Solubility is the maximum solute that dissolves in a fixed amount of solvent at a given temperature.
- Solubility of solids in liquids generally rises with temperature; solubility of gases in liquids generally falls.
- Crystallization forms pure crystals from a saturated solution, leaving impurities in the mother liquor.
- Distillation separates two miscible liquids whose boiling points differ by at least about 25 °C.
- Fractional distillation separates components whose boiling points differ by less than 25 °C, as in a refinery.
- Paper chromatography separates soluble components by how fast each one climbs the paper.
- Two immiscible liquids are separated in a separating funnel using the difference in their densities.
- Sublimation is a solid changing directly into vapour; deposition is the reverse.
- An alloy is a homogeneous mixture of metals and cannot be separated by physical methods.
- A suspension has particles above 1000 nm; they are visible, they settle and they can be filtered out.
- Centrifugation uses the centrifugal force to drive denser particles to the bottom of a spinning tube.
- Coagulation makes fine particles clump together so they can settle; alum does this in water and acid does it in milk.
- A colloid has particles of 1 to 1000 nm; it is stable, it cannot be filtered, and blood is one.
- A colloid has a dispersed phase and a dispersion medium; a liquid-in-liquid colloid is an emulsion.
- The Tyndall effect is the scattering of light by particles, shown by colloids and suspensions but not by true solutions.
Exploring Mixtures and their Separation
Class 9 — Chapter 5
5.1
Classifying Mixtures
homogeneous vs heterogeneous; uniform composition
5.2
Solutions
solute, solvent, concentration, solubility, saturated
5.3
Separating Homogeneous Mixtures
crystallization, distillation, paper chromatography
5.4
Separating Heterogeneous Mixtures
separating funnel, sublimation, alloys, centrifugation, coagulation, colloids
5.5
Tyndall Effect
scattering of light; dispersed phase; emulsions
Key Terms
- Mixture
- Two or more substances mixed together without any new substance being formed.
- Homogeneous mixture
- A mixture whose composition is the same throughout; also called a solution.
- Heterogeneous mixture
- A mixture whose composition is not the same throughout.
- Solute
- The substance that dissolves, usually present in the smaller quantity.
- Solvent
- The substance that dissolves the solute, usually present in the larger quantity.
- Solution
- The homogeneous mixture formed when a solute dissolves in a solvent.
- Concentration
- The amount of solute dissolved in a given amount of solvent or solution.
- % m/m
- Mass of solute divided by mass of solution, multiplied by 100.
- % m/v
- Mass of solute divided by volume of solution, multiplied by 100.
- % v/v
- Volume of solute divided by volume of solution, multiplied by 100.
- Solubility
- The maximum amount of solute that dissolves in a fixed quantity of solvent at a given temperature.
- Saturated solution
- A solution that cannot dissolve any more solute at that temperature.
- Unsaturated solution
- A solution that can still dissolve more solute at that temperature.
- Solubility curve
- A graph of solubility plotted against temperature.
- Crystal
- A solid whose particles are arranged in a regular geometric pattern.
- Crystallization
- The process of forming crystals from a saturated solution.
- Mother liquor
- The solution left behind after crystals have separated out, holding the impurities.
- Miscible liquids
- Liquids that mix into each other uniformly, such as acetone and water.
- Distillation
- Separating miscible liquids by boiling off the one with the lower boiling point and condensing it.
- Distillate
- The pure liquid collected after the vapour is condensed.
- Fractional distillation
- Separating components whose boiling points differ by less than 25 °C, as with crude oil.
- Paper chromatography
- Separating soluble components of a mixture by how fast each moves up a paper strip.
- Immiscible liquids
- Liquids that do not mix and form two separate layers, such as oil and water.
- Separating funnel
- A glass funnel with a stopcock, used to separate two immiscible liquids.
- Density
- Mass divided by volume; the denser liquid settles below the lighter one.
- Sublimation
- A solid changing directly into vapour without passing through the liquid state.
- Deposition
- Vapour changing directly back into a solid without passing through the liquid state.
- Dry ice
- Solid carbon dioxide, which sublimes and is used for ice cream storage.
- Alloy
- A homogeneous mixture of two or more metals, or of a metal and a non-metal.
- Suspension
- A heterogeneous mixture in which undissolved solid particles stay suspended in a medium.
- Centrifugation
- Spinning a mixture at high speed so the denser particles are driven to the bottom of the tube.
- Centrifugal force
- The outward force acting on a body moving in a circular path.
- Paperfuge
- A low-cost centrifuge made from a cardboard disc and thread, needing no electricity.
- Coagulation
- Fine suspended particles joining together into larger clumps so that they can settle.
- Coagulant
- The substance that causes coagulation, such as alum in water or lemon juice in milk.
- Sedimentation
- The settling of heavy particles at the bottom under gravity.
- Decantation
- Gently pouring off the clear liquid from above the settled solid.
- Colloid
- A heterogeneous mixture with particles of 1 to 1000 nm that never settle and cannot be filtered.
- Dispersed phase
- The particles scattered through a colloid, corresponding to the solute.
- Dispersion medium
- The medium in which those particles are scattered, corresponding to the solvent.
- Emulsion
- A colloid in which both the dispersed phase and the dispersion medium are liquids.
- Emulsifying agent
- A substance added to hold an emulsion together, such as the proteins in milk.
- Aerosol
- A colloid of liquid droplets or solid particles dispersed in a gas, such as a cloud.
- Tyndall effect
- The scattering of a beam of light by the particles of a colloid or suspension.
