elements, compounds and mixtures

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  • Created by: sophie_kk
  • Created on: 23-11-19 16:25
elements
substances that cannot be split into anything simpler by chemical means
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compounds
two or more elements chemically combined
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mixtures
various substances mixed together with no chemical reactions
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difference between mixtures and compounds
proportions in a compound are fixed, whereas in a mixture you could have any proportion you wanted to
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mixture of elements
each keep their own properties, but are changed in their compound form
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how can mixtures be separated?
by physical means eg changing temp or dissolving part of the mixture in water
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how to separate a mixture of iron and sulphur
use a magnet to attract the iron and leave the sulphur
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how to separate a mixture of hydrogen and oxygen gases
can cool the mixture to cause oxygen to condense, as it has a much higher condensing temp than hydrogen
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mpt and bpt
pure substances, like elements and pure compounds have a fixed mpt and bpt
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mpt and bpt in mixtures
usually melt or boil over a range of temps due to the presence of impurities that lowers the mpt of a substance, and raises the bpt
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filtration
separates a solid from a liquid by using a beaker and a funnel with filter paper inside.
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residue
substance left in filter paper
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filtrate
liquid that comes through filter paper
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what else can filtration be used for?
used to separate two solids if only one of them is soluble in water eg salt and rock
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crystallisation
separates a solute from a solution by heating the solution in an evaporating basin to boil off some of the water to leave just the saturated solution behind
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how can crystallisation be tested?
by dipping a glass rod into the solution and seeing if crystals form quickly on its surface when removed.
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making pure salt from rock salt
crushing rock salt and mixing it in hot water will dissolve the salt, but the rock impurities will be left behind. this can then be filtered, with the filtrate a now salt solution. we can then use crystallisation to obtain solid salt.
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simple distillation
used to separate the components of a solution , and we can also collect water using this method
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how does simple distillation work
water boils in a side arm flash and is condensed back to a liquid by the condenser., the salt will remain in the flask whereas the water will have evaporated, and enter a separate flask at the end of the condenser
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why is water always fed into the lower end?
always fed into the condenser at the lower end as it fills the condenser jacket better, and if water stops for any reason, the condenser jacket remains full of water
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fractional distillation
used to separate a mixture of liquids such as ethanol and water
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how does fractional distillation work?
by taking advantage of the different boiling points of water and eg ethanol - as ethanol boils fater it will evaporate into the fractionating column and remain a vapour all the way to the top of the condenser, and then out into the condenser
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cont
into the condenser. the liquid with the lower bpt will instead condense in the column and trickle back into the flask
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paper chromatography
can be used to separate a variety of mixtures
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paper chromatography experiment
draw a line in pencil across the paper about 1cm from the bottom. put a spot of the dye on the pencil line and allow to dry. suspend paper in beaker of water below pencil line. put a lid on beaker so atmosphere becomes saturated with solvent to stop
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cont
evaporation of solvent from surface of paper. when solvent has moved up to about 1cm from top remove and draw a line to the where the solvent has travelled to (solvent front). leave to dry so solvent evaporates
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retardation equation
retardation factor = distance ,moved by a spot (from pencil line) / distance moved by the solvent front (from the pencil line)
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Other cards in this set

Card 2

Front

compounds

Back

two or more elements chemically combined

Card 3

Front

mixtures

Back

Preview of the front of card 3

Card 4

Front

difference between mixtures and compounds

Back

Preview of the front of card 4

Card 5

Front

mixture of elements

Back

Preview of the front of card 5
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