cc2 Flashcards
What is a pure substance
Made up of a single element or compound
What is an element
All atoms are the same
What is a compound
Contains two or more different elements chemically combined in a fixed position
What is a mixture
Different elements or compounds not chemically joined
What is a molecule
Any element chemically joined
What is filtration used for
To separate an insoluble solid from a liquid
What are the steps of filtration
Pour the mixture through the filter paper that is in the funnel.
Then the liquid part will run through whilst leaving behind the solid residue
What is crystillsation used for
To separate a soluble solid from a solution
What are the steps of crystallisation
1) Pour solution into evaporating dish and gently heat.
2) Some of the water will evaporate and solution will get more concentrated
3) Once you see crystals forming you stop heating and leave solution to cool
4) Cooling will lead to more crystals forming as solids are less soluble at colder temperatures
5) Filter out crystals and dry
What is paper chromatography used for
Paper chromatography allows us to separate substances based on their different solubilities
What are the steps of Paper chromatography
1) Draw a line at the bottom of the paper (baseline) in pencil as the pencil is insoluble
2) Add sample of ink
3) Put paper into solvent but do not submerge the ink and put the lid on top
4) The solvent will move up the paper and you will see different dyes forming spots on the paper
5) Remove paper from beaker before solvent reaches the top and mark distance solvent has moved (solvent front)
What is the mobile phase
Molecules can move so its the solvent
What is the stationary phase
Molecules can’t move so its the paper
How do you calculate the RF value
distance travelled by solute/distance travelled by solvent
What is simple distillation used for
Separating a liquid from a solution
What are the steps for simple distillation
1) Pour the solution into the distillation flask
2) Gradually heat the distillation flask. Starts to evaporate turning into vapour
3) Water vapour passes into the condenser where its cooled and condensed and turns back into liquid
4) You will end up with a solid in a flask and liquid in beaker
What is fractional distillation used for
To separate a mixture of different liquids with different boiling points
What are the steps for fractional distillation
1) Put your mixture in a flask and attach the fractionating column and condenser
2) Gradually heat the flask. The different liquids will have different boiling points so will evaporate at different temperatures
3) Liquid with the lowest boiling point will evaporate first. When the temp on the thermometer matches boiling point of this liquid it will reach the top of the column
4) Liquid with higher boiling point may start to evaporate. But column is cooler towards top so will condense and run back down
5) When the first liquid has been collected raise the temperature until next one reaches top
What are some features of the composition of a pure substance?
The composition cannot be changed.
The composition is the same in all parts of a piece of the substance (e.g. pure gold contains only gold atoms).
What are the physical properties of a pure substance?
All of the pure substance will melt at the same temperature until all of the substance has changed state.
Do mixtures have a sharp melting points?
No, a mixture doesn’t have a sharp melting point.
How can you tell the difference between a pure and impure substance in a heating curve?
A pure substance has a sharp melting point (flat curve on melting point) and curved gradual lines whereas an impure substance has straight lines and doesn’t have a sharp melting point (line is not flat on melting point).
What is a saturated solution?
A solution that contains the maximum amount of solute that can dissolve in that amount of solvent at that temperature.
What laboratory apparatus is needed for filtration?
Filter paper, Suspension, Beaker, Filter funnel.
What laboratory apparatus is needed for crystallisation?
Evaporating basin, Filtrate, Boiling water, Gause, Bunsen burner.
What is a risk assessment for crystallisation?
The risks from spitting can be reduced by wearing eye protection, Removing the bunsen burner before the solution is completely dry and Using steam to heat the evaporating basin gently.
What apparatus is needed for distillation?
Distillation flask, Thermometer, Condenser, Cooled water, Delivery tube, Beaker.
What is desalination?
A process that produces fresh drinking water by separating the water from the salts in salty water.
How can desalination simply be achieved?
Desalination can simply be achieved by using the process of simple distillation.
How does simple distillation for desalination work?
Water is separated from dissolved salts using simple distillation. Sea water is heated so that water vapour leaves it quickly. This vapour is then cooled and condensed, forming water without the dissolved salts.
Is simple distillation a suitable method for producing large volumes of drinking water?
No, as a lot of energy must be transferred to sea water during simple distillation which will be a challenge for larger amount.
What factors count towards something being potable
Low microbes
Low levels of contaminating substances
How do you make waste and ground water potable
Sedimentation: Large insoluble particles will sink to the bottom of the water
Filtration: Water is filtered through beds of sand which removes small insoluble particles
Chlorination: Chlorine gas is put through water to kill microbes
How is water used in chemical analysis
Must be pure because of dissolved salts could react with the substances you are analysing leaving you with false results
