Section 1 b) Summary

An atom is the smallest existing chemical particle with an equal number of protons and electrons, and as a result has no charge. Each atom is a chemical element, which can react with each other to form compounds or physically combine to make a mixture. 

A compound is a substance formed by the chemical union of two or more chemical elements, with a definite, unchanging ratio. It has its own properties, different from the properties of its parts, and requires chemical reactions to be separated. 

A mixture is made from different substances that are not chemically bonded. Each of the substances within a mixture retains its own properties, and the ratio is not fixed. The substances are easily physically separated. 

Methods of separation include:

Filtration: Separating insoluble particles from a liquid

Passing a mixture through a filter funnel.

Evaporation: Removing liquid from a solution

Heating a solution to boiling point until the liquid is gone.

Chromatography: Separating controlled substances or dyes

Placing dots on chromatography paper and letting it run up the paper with capillary action.

Distillation: Separating liquids from each other. Simple - two liquids. Fractional - many liquids, involving a fractionating column.

Boiling and condensing liquids of different boiling temperatures. 

Chemical particles disperse through a fluid through diffusion and dilution. Diffusion is the net movement of particles from an area of high concentration to an area of low concentration. 

This can be demonstrated using experiments between hydrochloric acid  and ammonia, or bromine in a glass cylinder, as well as by placing food dye in water. The dispersal of particles can be seen through the experiments described here (specification)

Section 1 b) Key Words

Atom: The smallest particle of a chemical element that can exist.

Chromatography: The separation of different particles of a solution e.g. pigments in ink, by placing them on paper and allowing a solvent to transport the particles up the paper to different distances through capillary action.

Compound: Two or more chemically bonded elements. They can be ionic or covalent.

Crystallisation: The formation of crystals through evaporation

Diffusion: The net movement of particles from an area of high concentration to an area of low concentration.

Dilution: Making a substance weaker (e.g. HCl can be diluted so it is less corrosive, food dye disperses through a liquid and becomes weaker) through the addition of other substances.

Element: A substance found on the periodic table that cannot chemically be split up into simpler substances. Its atoms have equal numbers of electrons and protons, resulting in balanced charge.

Evaporation: The state change of liquid to vapor, used to separate a solid from a liquid solution.

Filtration: Separation using a funnel and filter paper to remove large, insoluble particles.

Fractional distillation: Heating a mixture of liquids into a fractionating column to separate them into fractions which differ in boiling point. The gases then pass through a a tube where they are condensed and collected as a liquid again.

Magnetic separation: Separation of magnetic and non-magnetic substances, used industrially in recycling plants, etc.

Mixture: Two or more compounds or elements that are physically mixed but not chemically bonded, e.g. air or steel.

Molecule: A group of atoms bonded together in the simplest form of a chemical compound that can take part in a chemical reaction.

Separation: Techniques of removing different parts of a mixture from each other to obtain substances combined within it.

Sieving: Removing larger insoluble particles from smaller insoluble particles by passing it through a sieve. Different sized holes in sieves can be used for different purposes

Simple distillation: Separating a mixture of liquids through heating, then condensing the vapor and collecting the purer substance Works best with mixtures containing few different chemicals (e.g. separating ethanol and water)

Section 1 b) Specification

1.4 describe and explain experiments to investigate the small size of particles
and their movement including:
i dilution of coloured solutions
ii diffusion experiments

Experiment 1: Dilution
Add a coloured substance to a solvent, e.g. food dye to a solvent, e.g. water. Over time, the intensity of the colour will decrease as it spreads throughout the liquid and dilutes- the concentration of the food dye decreases. Dilution increases at higher temperatures due to increased kinetic energy of particles, so applying heat decreases the time it takes for the dye to become fully diluted.

Experiment 2: Diffusion
Using a glass tube, place cotton wool soaked in ammonia solution at one side of the tube, and cotton wool soaked in hydrochloric acid at the other end. Both ends should be sealed with bungs. After a few minutes, a white ring of ammonium chloride will form in the tube, closer to the hydrochloric acid end. This tells us that the particles have diffused away from their respective ends to collide and react. The ammonia particles are smaller than the hydrogen chloride particles, and therefore move faster which is why the ring forms closer to the hydrochloric acid.

Experiment 3: Diffusion
Place liquid bromine at the bottom of a glass jar, and another empty jar upside down on top of it. As the bromine begins to evaporate, you can observe the volume of liquid decreasing, and the gas in the jar changing colour as the darker-coloured bromine particles diffuse upwards.

1.5 understand the terms atom and molecule

An atom is the smallest particle of an element that can exist. It has balanced charge (the same number of positively charged protons and negatively charged electrons) and a mass relative to carbon (12), made up of the neutrons and protons, each with mass of 1.
A molecule is a group of atoms bonded together, the smallest unit of a chemical compound that can take part in a chemical reaction, e.g. H2O

1.6 understand the differences between elements, compounds and mixtures

An element is one type of atom found on the periodic table, sometimes found bonded to another atom of the same element, e.g. O2, but it is always pure.
A compound is two or more elements chemically bonded in fixed proportions to form a new molecule, e.g. CO2
A mixture is two or more compounds or elements that are not chemically bonded, e.g. air, or a metal alloy such as steel.

1.7 describe experimental techniques for the separation of mixtures, including
simple distillation, fractional distillation, filtration, crystallisation and paper
chromatography

Solutions can be separated using a number of different techniques based on the physical differences of the substance (e.g. soluble and insoluble compounds). These include distillation, decanting, sieving, filtration, chromatography, crystallisation and magnetic separation.

Simple distillation: A liquid is boiled in a distilling flask, and the vapor travels through a tube, where thermal energy is passed to the cool water outside it and the vapor condenses into a liquid. The purified liquid then trickles out into a beaker. This generally is used to separate two liquids in a mixture, with different boiling points (e.g. ethanol and water)

Fractional distillation: The apparatus is similar to simple distillation, but the addition of a fractionating column filled with glass or plastic beads that allows better separation between the fractions due to condensation and re-evaporation occurring on the surface of each bead (distilling the mixture repeatedly). This allows the separation of more complex mixtures of liquids.
More on distillation

Filtration: A mixture is passed through a funnel with filter paper in it. The insoluble solid is left on the filter funnel, while the solution passes through the paper as the particles are small enough to fit through the gaps in the paper. This is used to separated a solution and insoluble particles.

Evaporation: A solution is heated to evaporate the liquid (e.g. water) leaving behind a solid that was previously dissolved. This is used to retrieve soluble compounds from solutions.

Crystallisation: A solution (e.g. aqueous sodium chloride) is heated to its boiling point, allowing the liquid, in this case the water, to partially evaporate. The solution is then left over a period of time, often several days to allow further water to evaporate at a lower temperature, causing crystals to form.

Chromatography: Different pigments in a mixture can be separated using chromatography. Dots of dye are placed at regularly spaced intervals at the bottom of a piece of chromatography paper, and the paper is placed in a beaker of solvent (the solvent should not reach the dye so it isn't dissolved and dissipated into the solution). The solvent will travel up the paper, and dissolve the pigments. Heavier pigments will be carried a shorter distance than pigments with smaller particles.

1.8 explain how information from chromatograms can be used to identify the
composition of a mixture. 

Using a chromatogram, the composition of a mixture of dyes can be determined through comparison of different pigments. Different pigments are more or less water-soluble, and have different particle sizes, resulting in the pigments travelling a certain distance up the paper. By comparing a mixture of pigments, and marking the distance they travel, then comparing with individual pigments and the distance they travel, the composition can be determined. Pigments of the same kind will travel the same or similar distances.