States of Matter and Mixtures (1) Flashcards
What is the state change from
solid to gas?
sublimation
What is a
pure substance?
a substance that is completely made up of a single element or compound
What is a
mixture?
a substance that contains more than one compound or different elements that aren’t all part of a single compound
How can you
test the purity of a substance?
By measuring its melting point and comparing it with the melting point of a pure substance.
A chemically pure substance will have a specific, sharp boiling or melting point.
If a substance is a mixture or impure, then it will melt gradually over a range of temperatures.
What is
simple distillation used for?
separating out a liquid from a mixture
e.g. pure water from sea water
the substances must have boiling points significantly apart from one another
Describe an experiment that uses
simple distillation to separate pure water from sea water.
(5 steps)
- First, set up the necessary equipment.
- Next, pour the solution into a distillation flask.
- Gradually heat the distillation flask. The water will evaporate first (as it has the lowest boiling point).
- As the vapour rises it passes into the condenser, where it is cooled and condenses before collecting in the beaker.
- Components of the mixture with higher boiling points are left behind in the flask, resulting in a more concentrated salt solution remaining.
What is
fractional distillation used for?
it is used for separating a mixture of different liquids, especially when the liquids have similar boiling points
Describe how you would carry out
fractional distillation.
(7 steps)
- Set up the necessary equipment.
- Gradually heat the distillation flask.
- The liquid with the lowest boiling point evaporates first.
- When the temperature on the thermometer matches the boiling point of this liquid, its vapour will have reached the top of the column and passed into the condenser.
- It will then cool and condense and collect in the beaker. This pure liquid can now be collected.
- Liquids with higher boiling points might also start to evaporate. But the column is cooler towards the top. So they will rise partly before condensing and running back down towards the flask.
- When the first liquid has been collected, raise the temperature to the next lowest boiling point of the liquids in the mixture.
What is
filtration used for?
it is used to separate an insoluble solid from a liquid
Describe the process of
filtration.
(4 steps)
- Fold a piece of filter paper into a cone.
- Place the filter paper point down into a filter funnel that’s sitting in the neck of a conical flask.
- Pour the mixture containing the insoluble solid into the funnel lined by the filter paper. Make sure that none of the mixture goes over the top or down the side of the filter paper.
- The liquid will pass through the filter paper but the solid won’t - it will be left behind in the funnel.
What is
crystallisation used for?
separating a soluble product from a solution
Describe the process of
crystallisation.
(5 steps)
- Place an evaporating dish on top of a tripod with a gauze mat. Place a bunsen burner underneath the tripod.
- Pour the solution into the evaporating dish and gently heat it. Some of the water will evaporate and the solution will become more concentrated.
- When you see crystals start to form, remove the dish from the heat and leave the solution to cool.
- The dissolved compound should start to form crystals as it becomes insoluble in the cold, highly concentrated solution.
- Filter the crystals out of the solution, and leave them in a warm place to dry.
What is
chromatography used for?
separating a mixture of soluble substances and identifying them
What is the
mobile phase
of chromatography?
the molecules can move
this is always a liquid or a gas
What is the
stationary phase
of chromatography?
the molecules can’t move
this can be a solid or a really thick liquid
How do the
components in the mixture separate
in chromatography?
Each of the chemicals in a mixture will spend different amounts of time dissolved in the mobile phase and stuck to the stationary phase.
How fast a chemical moves over the stationary phase depends on how it ‘distributes’ itself between each of the two phases - the more time it spends in the moble phase, the faster it will move.
What are the
stationary and mobile phases in paper chromatography?
stationary phase - pieace of filter paper
mobile phase - liquid solvent (e.g. water or ethanol)
Describe how you would
use paper chromatography to separate different dyes in an ink.
(7 steps)
- Draw a line near the bottom of a sheet of filter paper (using a pencil). This is known as the baseline.
- Place a small amount of ink on the line in a single place.
- Put the sheet up upright in a beaker of solvent. Make sure the ink isn’t touching the solvent initially so that it doesn’t get washed away.
- The solvent will start to move up the paper. When the chemicals in the ink dissolve in the solvent, they will move up the paper too.
- The different dyes in the ink will move up the paper at different rates, so the dyes will separate out and form spots in different places. If any of the dyes in the ink are insoluble in the solvent you’ve used, they’ll stay on the baseline.
- The point the solvent has reached as it moves up the paper is known as the solvent front. When the solvent front has nearly reached the top of the paper, take the paper out of the beaker and draw a line with a pencil along the solvent front.
- Leave to dry.
the end result is a pattern of spots called a chromatogram
What factors affect the
distance a compound moves
in paper chromatography? (2)
- how soluble they are in the solvent
- how attracted they are to the paper
Molecules with a higher solubility in the solvent, and which are less attracted to the paper, will spend more time in the mobile phase - and they’ll be caried further up the paper.
What equation allows you to calculate the
Rf value of a substance?
distance travelled by solute / distance travelled by solvent
How can chromatography help with
identifying a pure substance?
A pure substance won’t be separated by chromatography - it’ll move as one spot.
An impure substance will separate out during chromatography, and will produce at least two spots.
How could you
analyse a mixture using a combination of simple distillation and chromatography?
You could use simple distillation to work out what solvent the ink contains (assuming the solvent has the lowest boiling point of all the substances in the ink, and will evaporate first). The boiling point could be compared to the boiling points of common solvents.
After evaporating off the solvent, you could then carry out paper chromatography on a sample of the ink. This will separate out the different dyes in the ink, so that you can see how many there are. You can then compare the Rf values of the different spots with reference values.
What is
potable water?
water that is safe to drink
What are the
three main sources of water in the UK?
- surface water
- ground water
- waste water
Where does
surface water come from?
lakes, rivers and reservoirs
these sources start to run dry during the summer months
Where does
ground water come from?
from aquifers (rocks that trap water underground)
Where does
waste water come from?
from water that’s been contaminated by a human process
What are the
three main stages of all water purification?
- Filtration
- Sedimentation
- Chlorination
What occurs during
filtration?
(during the process of water purification) (2 things)
- A wire mesh screens out large twigs, etc
- Gravel and sand beds filter out any solid bits
What occurs during
sedimentation?
(during the process of water purification)
Iron sulfate or aluminium sulfate is added to the water which makes fine particles clump together and settle at the bottom.
What occurs during
chlorination?
(during the process of water purification)
Chlorine gas is bubbled through to kill harmful bacteria and other microbes.
Why don’t countries tend to
distill sea water as a source for water
if there are other sources of water available?
it requires a lot of energy, so is really expensive, especially if it’s used to produce large quantities of fresh water
What is
deionised water?
water that has had the ions that are present in normal tap water removed
this is because they can interfere with reactions
