TOPIC 2- States Of Matter And Mixtures Flashcards
Solids
Strong forces of attraction between molecules, holding them close together in fixed positions in a regular lattice arrangement. They have a definite shape and volume. They vibrate about their positions, vibrating more when heated (why they expand).
Liquids
Weaker force of attraction between particles so they are randomly arranged while sticking closely together. Definite volume but indefinite shape (they flow). Particles constantly move w random motion, vibrating more when heated (expanding).
Gases
Weak force of attraction between particles so they’re free to move far apart, the particles in gases travel in straight lines. Indefinite shape and volume with constant movement. When heated, they expand and increase pressure.
Solid to gas state change
Sublimation
Gas to solid state change
Deposition
Why can particles break bonds with each other during state changes?
They vibrate and gain enough energy to break the bonds.
What does filtration separate?
An insoluble solid from a liquid. You pour your mixture into a funnel with filter paper in it. The liquid filters through the filter paper, leaving a solid residue. The solid Hs been separated out from the liquid reaction mixture.
What does crystallisation separate?
A soluble solid from a solution. This is done by heating a solution in an evaporating dish until the water has evaporated/crystals appear. You should then leave it to cool and crystals will appear as they will become insoluble in the cold, highly concentrated solution. Then filter them and leave it to dry in a drying oven/ desiccator.
Desiccator
Contains chemicals that remove water from the surroundings.
What does chromatography separate?
Separates a mixture of soluble substances to identify them. You use PAPER CHROMATOGRAPHY to separate out dyes.
How you do paper chromatography?
Draw a baseline on the filter paper (using a pencil which is insoluble) and add different inks on it. Put it in a beaker of solvent (usually water but can be ethanol if the solute has low solubility) but make sure it doesn’t touch the baseline (so it doesn’t dissolve). Put a lid on the container (so it doesn’t evaporate). Each dye will move up the paper at different rates. Wait till water is nearly at top and take it out to dry.
End result of chromatography name? Why do the mobile phases end up in different places over the stationary phase?
Chromatogram. This happens because each of the chemicals in a mixture will spend different amounts of time dissolved in the mobile phase and stuck to the stationary phase.
What does the distance the solutes travel depend on?
The solvent/ paper used
Rf value
Distance travelled by solute/ distance travelled by solvent.
Measuring from centre of spot on baseline.
what do you do to check whether substances are the same?
You run a pure sample of a substance alongside a sample of the mixture itself, same Rf values mean that it’s likely to be the same substance.
What do chemists use to check identities of components?
Standard Reference Materials (SRM’s) that have controlled concentrations/ purities.
What does the strength between particles and materials depend on?
The material, the temperature and the pressure
Why does the temperature of matter going through state changes plateau?
Because it requires heat energy to break/strengthen the bonds
Mobile phase
The moving phase (solvent)
Stationary phase
Still phase (paper)
What’s distillation used to separate?
A liquid from a solution.
Purpose of simple distillation and the process.
Separates solutions of very different bp’s. Solution is heated in conical flask with bung and thermometer in top, evaporating liquid w lowest bp. Vapour travels into condenser (cold water is ran through it to cool it down), cools and condenses before being collected in a beaker at the end.
Risks of simple distillation
Mixture could boil over if heated too quickly > use a round conical flask (heats mixture slower), anti bumping granules (reduces violence of mixture) mineral wool (stops mixture from spitting) or heat it in hot water instead. Also, a flammable liquid could set alight and so needs to be heated with a water bath/ electric heater rather than a Bunsen.
Purpose of fractional distillation and its process.
Separates out a mixture of liquids with more similar melting points (in a lab or on an industrial scale), mainly used for crude oil refining. Industrial> have a fractionating column with a temperature gradient, insert your mixture (crude oil) into the bottom of the chamber. The fraction with the lowest bp will evaporate first and condense at the top fraction, fractions with lower bp’s will condense lower down in the column in their own fractionating chamber. These are then collected. This is safer than simple distillation as is kept in containers chamber whereas could explode if pressure gets too high.
Which state of matter holds the most energy?
Gases, then liquids and finally solids.
What do gases do when placed in a container?
Exert forces on the walls of the container.
Physical change
When a substance changes from state of matter to another. They are easy to undo.
Chemical change
They happen during chemical reactions, when bonds between atoms break, causing atoms o rearrange. The reactants are rearranged to form products. These are hard to reverse.
Why do solids eventually turn into gases?
This is because heating adds energy to particles, causing more vibrations between particles which weakens the forces between them and causes them to expand. At a certain temp, they can break free from their positions (melting). More energy weakens and breaks the bonds holding the liquid together so they can break their bonds completely as gases.
Below MP?
Solid
Above BP?
They are a gas.
Above MP?
They’re a liquid / gas
Below BP
They’re a solid/liquid
Pure
Made up of a single element/ compound.
How do you test the purity of a substance?
Via its melting points, use melting point apparatus to record exact melting point. If not, you can use a water bath and thermometer (although is less accurate to control temp).
Melting points of pure substances?
They have specific and sharp melting points, meaning that they can be compared with their expected to value to see whether pure.
Impure substance’s melting points?
They melt over a range of temperatures.
In chromatography, what does the amount of time spent in each phase depend on?
It depends on their solubility in the solvent and how attracted they are to the stationary phase.
What happens if you have colourless chemicals within your mixture on the chromatogram?
You spray the chromatogram with a locating agent.
Standard reference materials
Pure substances with controlled concentrations and purities.
Core practical investigation into composition of an ink?
Distill it (simple) to collect its solvent, assuming the solvent has a lower BP. The BP may tell you what the solvent is. Then go on to carry out paper chromatography alongside SRM (standard reference materials which produce reference values) to find out they dyes within the ink.
Potable water
Water that’s fit to drink
Where do we get potable water from in the UK?
Surface water, ground water and waste water
Where does surface water come from?
Lakes, rivers and reservoirs. These run dry in summer months and require much treatment.
Where does ground water come from?
Aquifers. In parts of SE England, 70% of water supply comes from ground water. Require little treatment.
Aquifers
Rocks that trap water underground
Where does waste water come from?
Water that has been contaminated by human processes. This is preferable to do rather than disposing of the water which then causes pollution. These need much treatment and are affected by levels of contaminants.
Where’s water purified?
water treatment plants
What processes occur at water treatment plants?
Filtration, sedimentation and chlorination
What does filtration compose of?
Wire meshes screen out large particles and gravel/ sand beds filter out other large solids.
What does sedimentation compose of?
Iron/ aluminium surface is added to the water, causing particles to clump together and settle at the bottom.
What does chlorination compose of?
Chlorine gas is bubbled through to kill harmful bacteria and microbes.
Is the water chemically pure after chlorination?
No because some soluble impurities cant be filtered out (including minerals that cause water hardness).
What do they do in hot countries to produce potable water?
They distill sea water. This is v energy intensive so is v expensive & isn’t used in UK.
What type of water is used in chemical analysis and why?
Deionised water as ions can interfere with chemical reactions and so give you a false result.
Deionised water
Water that has had the ions that are present in normal tap water removed.
