- Created by: keyaan Martin
- Created on: 20-03-17 17:56
States of matter
- State changes are physical changes. They can be reversed, and the chemical properties of the substance do not change.
- This is because the particles themselves do not change-only their arrangement, movement and amount of stored energy
- Particles are attracted to one another by weak forces of attraction, many of these forces are found in solids
- For evaporation to happen energy must be transferred from the surroundings to the particles.
- For condensation nto happen energy must be transferred from the particles to the surroundings
- A pure substance is something that cannot be changed and is the same in all parts of a piece of the substance
- A pure substance has the same fixed composition in all parts and so we cant seperate it into other substances using physical methods
- A mixture contains elements and/or compunds that are not chemically joined together
- You can use physical processes to seperate mixtures into diferent substances
- A mixture does not have a fixed composition
- When a solid melts, its particles gain enough energy to overcome the weak forces of attraction between them.
- They move further away from one another and the solid becomes liquid
- The temperutre at which this happens is the melting point
- A pure substance has the same composition in every part of it, and so its physical properties are the same every part
- Mixtures do not have fixed, sharp melting points
Filtration and crystallisation
- Filters are used to seperate mixtures, They let liquids or smaller pieces get through and the bigger pieces or the insoluble get trapped
- A solution is a mixture made of solutes in a liquid called a solvent
- Solutes can be evaporated from a solution by evaporating the solvent that leaves the solute behind which is called crystalisation.
- Is the cystals form slowly, the particles have longer to form which makes the a larger crystal
Filtration and crystallisation in the lab
- To filter a solution in the labortary, a filter funnel is lined with filter paper that has fine wholes. The insoluble substances wont be able to fit through the paper leaving the residue( the remaining mixture after the mixture has passed)
- The substance is then evaporated, however care must be taken not to overheat the solution once saturated, because hot crystals might spit out and might change chemically
- During crystalisation the risks from spitting can be reduced by wearing eye protection, removing the bunsen burner before before the solution is completely dry or using steam to heat the evaportaing basin gently
- Chramatography can be used to find out which colured compounds the mixture contains
- Paper chromatography is a simplier technique that works because some compounds dissolve better in a solvent then others
- When a solvent moves along the ***** of paper, it carries the diferent substances in the mixture at diferent speeds, so they seperate.
- The solvent is called the mobile phase.
- Paper chromatography can be used to distinguish between pure and impure substances, identify sunstances by comparing the pattern on the chromatogram with the patterns formed by known substances
- Rf = distance moved by the compound ÷ distance moved by the solvent
To make water pure we need to seperate it from the dissolved solids which is done by distillation
When mineral water evaporates, only the water turns to gas, and the other particles are left behind
As water vapour is pure, if you condense it you will get pure water
The apperatus used is called still
Fractional distillation differs from distillation only in that it separates a mixture into a number of different parts, called fractions.
A tall column is fitted above the mixture, with several condensers coming off at different heights. The column is hot at the bottom and cool at the top.
Substances with high boiling points condense at the bottom and substances with low boiling points condense at the top. Like distillation, fractional distillation works because the different substances in the mixture have different boiling points.
- Producing pure water from sea water is called desalination and can be achived using simple distilation
- Sea water is heated so that water leaves it quickly, the water vapour is then cooled which forms pure water
- Chemical anaysis involves using chemical reactions or sensitive manchines to identify substaces in a sample
- For example, water should not contain any dissolved salt, otherwise incorrect results will be obtained
- A reservoir is stored with water from rivers, lakes and aquifers. Fresh water from these sources contain objects such as leaves, small insoluble particles such as grit, soluble substances and bacteria and other micro-organsms
- Sieving, sedimention and filteration are all used to deal with these impurities.