States of Matter
Changes in state are physical which can be reversed easily.
| State | Arrangement | Movement | Relative Energy | |
|
↓ Sublimation ↓ |
Solid | Close together in regular pattern from strong forces of attraction | Vibrate about fixed point so fixed volume and shape | Little energy |
| During melting, solid is heated, and particles gain energy, weakening forces of attraction and eventually breaking from their points to become liquid at the melting point. Liquid to solid is known as freezing | ||||
| Liquid | Close together in random arrangement | Slide over each other to fit container | More energy than in solid state | |
| During evaporation, liquid is heated and particles gain even more energy, breaking all forces of attraction to become a gas at the boiling point. Gas to liquid known as condensation | ||||
| Gases | Far apart in random arrangement – no forces of attraction | Move quickly in all directions exerting pressure on walls | Particles have most energy | |
Separation
In Chemistry, the word ‘pure’ means that a substance is made of a single type of compound or element. Purity can be tested for by looking for sharp melting points. The best separation technique depends on the substances in the mixture.
| Technique | Used for | Method |
| Simple Distillation | Separating liquid from solution | Pour sample into distillation flask and set up beaker and condenser, running cold water through it. Heat flask until liquid evaporates. It will condense in the condenser and will be collected in its pure form in the beaker |
| Fractional Distillation | Separating mixture of liquids | Same as simple distillation, but add fractionating column with glass shards in it. Liquids will evaporate at different temperatures. Collect each liquid at its boiling point |
| Filtration | Insoluble solid from liquid | Put filter paper in funnel over conical flask and pour in mixture. Liquid will run through while solid residue remains |
| Crystallation | Soluble solid from solution | Pour solution in evaporating dish and heat until some water evaporates. Since it is more concentrated, leave on watch glass to form hydrated crystals |
| Chromatography | Separate soluble substances for identification | Draw a baseline and add mixture. Add solvent below the baseline and cover beaker to stop evaporation. Components spread as the mobile phase (the solvent) moves up the stationary phase. Chemicals are moved and will spend different amounts of time in solution depending on solubility and attraction to paper. Measure the distance travelled by each chemical and the solvent’s distance to the solvent front. Spray with locating agent if necessary. To identify components, compare Rf values to reference values for the particular solvent or pure sample runs
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CORE PRACTICAL: Separating Inks
A – Set up equipment for simple distillation as in the table above, with ink in the flask and its vapours carried away by a delivery tube through a condenser until it reaches the beaker
B – Heat ink as it simmers gently until the distillate has been collected and note maximum temperature to identify the solvent used in the sample
C – Drop the ink on the baseline of paper. Dip the paper in water below the baseline and allow for it to move up the paper and spread the inks
D – One dried, measure the distance travelled by the water and the distances moved by each dye E – Calculate Rf then compare to reference values for identification
Drinking Water
97% of Earth’s water is in oceans, but the concentration of salts in it is too high to drink. To purify water, simple distillation is used so pure water without dissolved salts can be separated from sea water. Due to the large amounts of energy required for this process it is not usually suitable, but in areas where energy resources are cheap or abundant, and there is high supply of sea water, such as in the Middle East, it can be used.
In the UK, water for drinking is often stored in reservoirs, which contain objects like twigs, small insoluble particles like grit, soluble substances like fertilisers and salts and microorganisms. To purify this water, water must be screened using a sieve (sedimentation) and filtered using beds of sand and gravel. During chlorination, bubbling chlorine through the water, microorganisms are killed
Water used in chemical analysis must be pure and as impure water may form precipitates, hiding the correct result