C2- Methods Of Seperating And Purifying Substances Flashcards
Tell me about the composition of a pure substance
It can’t be changed
It’s the same for all parts of a piece in that substance
We can’t seperate it into other substances
What’s a mixture
Contains elements and/or compounds that are not chemically joined together so you can use Physicsl processes to seperate them
Does not have s fixed composition eg the air- it can change and have more
Co2 and then less
What is a melting point
When the particles gain enough energy to overcome the weak forces of attraction between them
It’s a physical property (how a substance responds to forces and energy)
Tell me about pure substance melting points
It’s the same and is exact
A mixture can be a range
What can filters be used for
They can let smaller pieces or liquids through but trap bigger pieces or insoluble substances
What’s a solution
A mixture of solutes (dissolved substances) and in a liquid (solvent)
What’s crystallisation
Separating solutes from a solution by evaporating solvent to leave solutes behind
What’s a saturated solution
No more solute can be dissolved in a solvent at that temperature - if more solvent evaporates or cools them some
Solute leaves the solution
How do we filter solutions in s lab
A filter funnel with filter paper - the solution passes through to form filtrate and the stuff left is the residue
Tell me about crystallisation in a lab
You have the filtrate , evaporating basin, boiling water, gauze and a Bunsen burner to evaporate solvent and leave crystals of solute
What’s a risk assessment
The hazard of doing an experiment are identified
How can we reduce hazards in crystallisation
The risks of spitting can be reduced by wearing eye protection and removing the Bunsen burner before the solution is completely dry
What can chromatography do
Can be used to find out which coloured compounds a mixture contains - eg substances in oil paintings
Tell me about paper chromatography - how are colours separated
It carries different substances in the mixture at different speeds so it’s seperated
What is the solvent also known as In paper chromatography
Mobile phase
What’s the paper also known as
Stationary phase - through which the solvent and dissolved substances move
What’s the chromatogram
The paper with the seperated components
What’s the R(little f in bottom right corner)
Rf value
The distance the compound has risen divided by the solvent risen
Rf= distance moved by the spot divided by the distance moved by the solvent
The value of a particular compound does not change if the chromatography conditions used remain the same
Always less than 1
What can paper chromatography be used for
Distinguish between putt and impure substances
Identify substances by comparing the pattern on the chromatogram with the patterns formed by known substances
Identify substances by calculating Rf values
What’s is simple distillation
The evaporation and condensation of water to purify it
Water is heated in a conical flask and the vapour travels along the delivery tube where it condenses.
What do anti bumping granules do
They make liquid boil more smoothly - small bubbles of vapour form on the corners of the granules and reduce the risk of the liquid boiling over
What’s the distillate
The pure substance eg pure water
What’s fractional distillation
Separating 2 or more liquids
As those with lower Boiling points will evaporate more easily than others and will turn into vapour first
The first liquid to be collected contains the lowest boiling point
What can fractional distillation be used for
To seperate the different products in crude oil
Make alcoholic drinks such as whisky and vodka
To seperate out the gases in air, after the air has been cooled and turned into a liquid at -200 C
Why would a liquid with a lower boiling point reach the top of a fractionating column more quickly than one with a higher boiling point
At first vapour condenses when it hits the cool glass and drips back down into the flask- as the column gradually heats up there will be a temperature gradient - it will be hottest at the bottom so the fraction with the lowest boiling point will reach the top of the Column first and the vapour will then pass into the condenser
What’s desalination
Producing pure water from sea water
Can be achieved using simple distillation
How is sea water purified
It’s heater do the water vapour is heater leaving salts, the vapour is then condensed
What is chemical analysis
Using chemical reactions or sensitive machines to identify and measure the substances in a sample
What are aquifers
Underground rocks containing ground water
Why must the water NOT contain dissolved salts
They may react to form unexpected cloudy precipitates that may hide the correct result of the analysis
Machines may detect salts leading to an incorrect conclusions
What do fresh water from sources such as river, lakes and aquifers contains
Objects such as leaves and twigs
Small insoluble particles such as grit and silt
Soluble substances such as salts, pesticides and fertilisers
Bacteria and other microorganisms that may be harmful to health
What’s sedimentation
Allowing time for small particles To settle out
What’s chlorination
It’s added to water to kill microorganisms
Tell me how water is treated
Water from source is put in a sedimentation tank and then a filtration tower and then Chlorine is added and then water is stored in a tower and then distributed to homes
