IGCSE Chemistry: Measurement, Techniques, States, and Solutions

Stopwatch

Measures time in seconds/minutes.

Thermometer

Measures temperature/change in temperature.

Balance

Measures mass in grams.

Burette

Accurate volume to 0.1cm3 for any volume between 0.0 and 50.0 cm3.

Pipette

Accurate volume to 0.1cm3 for a fixed volume only.

Measuring cylinder

To measure an approximate volume.

Excess reagent

More than was required.

Filtration

Removes a solid from a liquid/solution.

Crystallisation

Removes a solvent from a solution.

Simple Distillation

Separates substances with very different boiling points.

Fractional Distillation

Separates substances with different boiling points using a temperature gradient.

Determining crystallisation/saturation point

If crystals form, the solution is at crystallisation point.

Purity

Check melting point/boiling point.

Impure substance

Melts/boils at a range of temperatures around the melting point/boiling point.

Fractionating column

A component used in fractional distillation that has a temperature gradient, hotter at the bottom and cooler at the top.

Condenser

A device required for both simple and fractional distillation that cools vapour and condenses it back into liquid.

Anti-bumping granules

Granules used in distillation to prevent the flask from bumping too much.

Boiling point (bp)

The temperature at which a substance changes from liquid to gas.

Rf value

A value used in chromatography to identify a substance, calculated as Distance moved by substance ÷ Distance moved by solvent.

Chromatography

A technique that separates molecules by size, mass, and solubility, often used for dyes or coloured substances.

Baseline/origin

The starting line on chromatography paper where samples are placed.

Solvent front

The furthest point reached by the solvent in chromatography.

Distance moved by substance

The distance a substance travels from the baseline in chromatography.

Distance moved by solvent

The distance the solvent travels from the baseline in chromatography.

Temperature gradient

A variation in temperature along the length of the fractionating column in fractional distillation.

Mixture

A combination of two or more substances that can be separated by physical means.

Flask

A container used to collect the liquid in distillation.

Beaker

A container that can also be used to collect the liquid in distillation.

Vapour

The gaseous state of a substance that is typically liquid at room temperature.

Chromatography paper

The medium used in chromatography to separate substances.

Watch glass

A glass dish used to cover the chromatography paper to prevent solvent evaporation.

Unknowns

Samples of substances whose identities are to be determined through chromatography.

Solvent

A liquid that dissolves a solute to form a solution, used in chromatography.

Collection

The process of gathering the separated substances after distillation or chromatography.

Separation

The act of dividing a mixture into its individual components.

Kinetic Particle Theory

The theory that explains how energy must be supplied or removed to change one state of matter to another.

Melting

The change from solid to liquid.

Boiling

The change from liquid to gas.

Freezing

The change from liquid to solid.

Condensation

The change from gas to liquid.

Sublimation

The direct change of a solid to a gas or gas to a solid without passing through the liquid state.

Brownian Motion

The random movement of particles, evidenced by suspended particles in a liquid moving in random directions.

Diffusion

The random movement and mixing of particles causing the substance to spread.

States of Matter

Matter may be solid, liquid, or gas.

Atoms

The basic units that make up all matter.

Molecules

Atoms combined together.

Compounds

Substances composed of two or more different types of atoms chemically bonded at a fixed ratio

Elements

Substances composed of only one type of atom.

Gas Laws

Properties of gases, including how they exert pressure and respond to temperature changes.

Pressure in gases

The force exerted by gas particles colliding with the surface of a container.

Temperature effect on gas

Increased temperature leads to faster movement of particles, causing more collisions and increased pressure.

Elasticity of gases

Increases in pressure lead to increases in volume as the container stretches.

Suspension

A mixture where solid particles are dispersed in a liquid.

Antibody based locating agent

A substance added to indicate the location of separated substances that have no color.

Rate of diffusion factors

Dependent upon molecular mass; lower molecular mass = faster diffusion, higher molecular mass = slower diffusion.

Temperature effect on diffusion

Higher temperature = faster diffusion, lower temperature = slower diffusion.

Evidence of diffusion

A perfume sprayed in one corner of the room spreads until the entire room is filled with that perfume.

Pure substances properties

Have a fixed mp and bp

Impure substances

Melt or boil at a range of temperatures, usually close to the mp/bp of the pure substance.

Salt on roads

Salt is put on roads during winter because water freezes at about -5°C rather than 0°C.

Dilution

A way of changing the concentration of a solution in a measured way.

Diluted solution example

The solution has been diluted to 10% of the original at each step.

Solute

A solid that can dissolve.

Solution

A solvent containing a dissolved solid.

Soluble meaning

A solid that can dissolve.

Insoluble

A solid that cannot dissolve.

Saturated solution

A solution with the maximum mass of a solute dissolved.

Crystallisation of saturated solutions

Saturated solutions crystallise quickly.

unit of solubility

Measured in grams per litre (g/L).

Solubility per 100g of solvent

The mass of solute that can dissolve in 100g of solvent.

Solubility curves

Plotted to determine the theoretical solubility of a substance at a particular temperature.

Mixtures

Made up of a range of different substances that are easily separated.

Identifying substances

Use the name and/or formula to identify what a substance is.

Atom

The simplest unit of matter.

Compound

Two or more atoms chemically joined in a fixed ratio.

Element

Composed of only one type of atom.

Impure

Contains more than one substance.

Pure

Contains only one substance.

Water of crystallisation/hydration

The water present in a fixed ratio when crystals form.