Section 11 - States of Matter and Mixtures

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What is a physical change?
When a substance changes from one state of matter to another.
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What happens when a solid is heated?
The particles vibrate more, which weakens the forces that hold the solid together. This makes it expand.
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What happens when a solid melts?
When they reach a certain temperature, the particles have enough energy to break free from their positions, so the solid turns into a liquid.
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What happens when a liquid evaporates?
The particles gain even more energy so they move faster, and they weaken and break their bonds.
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What is sublimation?
When a solid turns into a gas.
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What happens in a chemical reaction?
Chemical changes - when bonds between atoms break and the atoms change places. Reactants are re-arranged to form products.
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What does it mean if a substance is pure?
It is made up of a single element or compound.
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What is a mixture?
A substance with more than one compound presemt, or different elements which aren't all part of a single compound.
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Is air a compound, mixture or pure? Why?
It is a mixture as it consists of several different elements, such as oxygen, nitrogen, carbon dioxide, water vapour, etc.
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How can you test if a substance is pure?
By comparing the actual melting point of a sample of a substance to the expected value. Impure substances will melt over a rang of temperatures.
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What is filtration used for?
To separate an insoluble solid from a liquid.
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What is crystallisation used for?
To separate a soluble solid from a solution.
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What are the two phases in chromatography?
Stationary phase and mobile phase?
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What is the mobile phase?
Where the molecules can move. The solvent (water/ethanol).
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What is the stationary phase?
Where the molecules can't move. The filter paper.
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How do you work out the Rf value?
Distance travelled by solute divided by distance travelled by solvent.
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Why do you draw the line near the bottom of the paper using a pencil?
Because it's insoluble and won't move with the solvent.
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The amount of time the molecules spend in each phase depends on what?
1) How soluble they are in the solvent. 2) How attracted they are to the stationary phase.
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If the chemicals in your mixture are colourless (e.g. amino acids), what do you do?
You spray the chromatogram with a locating agent to show where the spots are.
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What is the Rf value?
The ratio between the distance travelled by the dissolved substance and the solvent.
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Where do we get our water from?
Surface water, ground water and waste water.
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Through what processes is water purified?
Filtration, sedimentation and chorination.
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How does filtration purify water?
A wire mesh screens out large twigs and then gravel and sand beds filter out any other solid bits.
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How does sedimentation purify water?
Iron sulfate or aluminium sulfate is added to the water, which makes fine particles clump together and settle at the bottom.
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How does chlorination purify water?
Chlorine gas is bubbled through to kill harmful bacteria and other microbes.
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How else can you get potable water?
By distilling sea water.
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Why isn't sea water distilled in the UK?
Because it requires lots of energy so it is very expensive.
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What kind of water should be used in chemical analysis?
Deionised water.
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What is deionised water?
Water that has had the ions (calcium, iron and copper ions) that are present in normal tap water removed.
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Why is deionised water used?
Because the ions can interfere with reactions and give the experiment a false result.
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Other cards in this set

Card 2

Front

What happens when a solid is heated?

Back

The particles vibrate more, which weakens the forces that hold the solid together. This makes it expand.

Card 3

Front

What happens when a solid melts?

Back

Preview of the front of card 3

Card 4

Front

What happens when a liquid evaporates?

Back

Preview of the front of card 4

Card 5

Front

What is sublimation?

Back

Preview of the front of card 5
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