Topic 2 - States of matter and mixtures

In a gas, particles have the most energy and are therefore able to spread out. They can flow because their particles can move in all directions and can be compressed because their particles are far apart and have space to move into.

In a liquid, particles have greater energy than a solid and are able to flow because their particles can move around. However, the particles are close (fixed) so together so they can’t be easily compressed.

A solid has low energy and particles are fixed. They cannot flow because their particles can’t move and cannot be compressed because their particles are close together.

Physical changes (such as state changes) involve the forces between the particles of the substances but the particles themselves don’t change. In chemical a new product is formed.

solid​ ​→​ ​liquid:​ ​melting liquid​ ​→​ ​solid:​ ​freezing liquid​ ​→​ ​gas:​ ​boiling/evaporating gas​ ​→​ ​liquid:​ ​condensing

Energy must be transferred, by heating, to a substance. During this, the particles gain energy which is used to break or overcome some of the bonds between particles (or all the bonds during evaporation)

Energy must be transferred from a substance to the environment. During this, the particles lose energy as bonds form between the particles.

A pure substance consists only of one element or one compound

Two or more different substances, which are not chemically joined together.

It is used to separate a solvent from a solution. The dissolved solute must have a higher boiling point than the solvent. The solution is heated by a Bunsen burner. The water vapour cools in the condenser and drips into a beaker as the pure solvent. The solute remains in the beaker.

It is used to separate different liquids from a mixture of liquids. The different liquids must each have different boiling points. When the mixture is heated it evaporates and vapour rises through a column which is hot at the bottom and cold at the top. The substance with the lowest boiling point is collected at the top of the column as it moves into the condenser and it comes out of this into a beaker as a pure liquid.

It is used to separate an insoluble solid from a liquid. A funnel with filter paper is placed in a beaker. The mixture is poured through the filter funnel. The liquid drips through the filter paper but the solid particles are caught in the paper.

It is used to separate a soluble salt from the solution it was dissolved in. An evaporating basin with the solution in it is placed on a tripod over a Bunsen burner. The liquid evaporates and solid crystals are left behind. To obtain large, regularly-shaped crystals use a boiling water bath rather than a tripod and Bunsen burner and stop heating before all the solvent has evaporated, filter or pour away the excess liquid once it has cooled. You can dry the crystals using a warm oven.

It is used to separate mixtures made up of soluble substances and give information to help identify them. Draw a baseline on the chromatography paper using a pencil. Place a spot of each sample mixture on the baseline. Pour the solvent into a beaker. Place a rod over the beaker and attach the paper to it so just the paper’s base touches the solvent. The solvent will travel up the paper taking soluble pigments from the sample mixture with it so they create different spots along the paper. Remove it before the solvent reaches the top. This is a chromatogram.

The separation of mixtures of soluble substances by running a solvent (mobile phase) through the mixture on the paper (the paper contains the stationary phase), which causes the substances to move at different rates over the paper

Pure substances should only have one spot on the chromatogram while mixtures will have more than one

An Rf value of 0 would mean that the substance is insoluble in the mobile phase (the solvent being used) and so the spot remains on the start line. An Rf value of 1 would mean that the substance has moved as far as the solvent front, so it is very strongly attracted to the mobile phase and not attracted to the stationary phase

Rf = distance travelled by substance/distance travelled by solvent

-Large objects are removed by screening using grids -A coarse filter bed made from clean sand and gravel removes larger insoluble grit particles -In sedimentation, aluminium sulfate is added to clump smaller insoluble particles together, which then settle at the bottom in a sedimentation tank -In filtration, a fine filter bed removes very small insoluble particles -In chlorination, chlorine gas is added to kill harmful microorganisms

Filter the seawater, boil it and then the water vapour is cooled and condenses to form pure water.

Must​ ​be​​ pure​​ because​​ any​ ​dissolved​​ salts​​ could​​ react​​ with​ ​the​ substances you​​ are​​ analysing,​ ​leaving​​ you​​ with​​ a ​ ​false​ result. This is why water produced by distillation is useful in the lab for dissolving substances.