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Doc Brown's Chemistry
KS3
SCIENCE-Chemistry QCA
Unit 7H Solutions
KS3 Quizzes or task sheets based on this summary: four word-fill worksheets * multiple
choice quiz * X-word * matching
pair quiz (printout/drag-drop version)
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7H
Solutions (solubility, salt purification and
chromatography etc.)
 QCA 7H "Solutions"
Multiple Choice Questions for Science revision
on particle models of mixtures, rock salt
purification, solute/solvent/solution/solubility, methods of separating
mixtures - filtration, evaporation, distillation, chromatography.
7Hwf1-4
four handy linked word-fill
worksheets * 7Hwf2 * 7Hwf3 *
7Hwf4 *
The BIG hard
on-line crossword puzzle 
(with letter hints), printout of the BIG version
OR the smaller
EASIER
(with letter hints),
printout
of the smaller EASIER version
matching pair exercise on keywords or
drag
& drop version or printout
The
7H
crossword and word-fill
* KS3 Science multiple Choice Quizzes for
chemistry, worksheets and practice chemistry questions for pupils revising Key
Stage 3 science tests revision help for secondary students *
In this unit you should learn to ...
- extend your knowledge of dissolving and the separation of the components
of a solution and relate this to particle theory
- begin to distinguish between a ‘pure’ substance and a mixture
- apply the particle model of solids, liquids and gases in a range of
contexts
- make measurements of temperature and mass
- describe and interpret patterns in graphs and chromatograms
- make predictions from graphs and data about solubility
- investigate, and explain, how a sample of pure salt can be obtained from a sample of
rock salt, evaluating the method in terms of salt obtained
- classify some solids as soluble or insoluble and
explain the meaning of the term ‘urated solution’
- describe how mixtures
can be separated by distillation and chromatography
- use the
particle model to explain what happens when a solid dissolves in water,
explaining why mass is conserved
Its handy if you ...
- have had experience of dissolving solids in water and know that not all
are soluble
- have separated mixtures of solids and liquids
- know that not all liquids contain water
- know that all materials are made up of very small particles
Some important words for you to understand, use
and spell correctly ...
- words and phrases relating to dissolving, eg solution, solute,
solvent, soluble, insoluble, saturated solution
- words and phrases relating to the separation of mixtures,
eg
filtration, distillation, chromatography, chromatogram
- words and phrases relating to explanations using the particle model,
eg
particle, attracted, mixing, mingling
- words and phrases relating to scientific enquiry,
eg prediction,
evaluate, interpret
- words with similar spelling but different meanings, and use them in a
consistently correct way, eg affect, effect
How can we tell whether a liquid is a mixture?
- that some solids dissolve in liquids and others do not
- that many common materials are mixtures
and mixtures can be separated
- selection of liquids, eg distilled water
or deionised water, seawater, a suspension of chalk in water, ethanol,
copper sulphate solution, and ask is it
water? is it pure?
- devise techniques, eg filter, evaporate to dryness, to find out
whether a liquid is a mixture or not
- learn the terms ‘soluble’, 'solvent',
'solution‘, 'insoluble’ and ‘solute’
- name some solids that dissolve in water and some that do not
- identify the components of some mixtures,
eg seawater is water
with salt and other solids dissolved in it
How much salt can we get from rock salt?
- use knowledge about separating mixtures to obtain a sample of
salt from rock salt
- that salt comes from a variety of sources and has many uses
- although
the salt dissolves, it doesn’t disappear!
- the occurrence, extraction
and uses of salt - relate this to processes used in the laboratory
- explain why the mass of the salt sample was less than the mass of
rock salt
What happens to the solute when a solution is made?
- that when a solute dissolves, mass is conserved
- that when a solute dissolves, the solute and solvent particles
intermingle
- draw the water particles (solvent) before and after the
addition of salt (solute) and use this to explain, eg that mass is
conserved, or why filtering will not separate the salt
- mixing two liquids,
eg
ethanol and water or oil and water - which mix/dissolve in each other?
How can we separate solvents from solutes?
- distillation can be used to separate a liquid from the
solids which are dissolved in it eg ink solution
- distillation is a process in which
evaporation/boiling of a liquid is followed by condensation by cooling
- it is often very important to separate and collect
the liquid, eg in purifying water.
- how they could you obtain drinkable water from
seawater?, eg in an area
where there is a lot of seawater, but no fresh water.
- describe how the solvent could be separated from the solute by
distillation
- distillation separation works because the solvent changes to a
gas and back to a liquid, but the solute does not evaporate
- find out about desalination
plants or how distillation is used to separate liquids, eg crude oil.
How can chromatography separate and identify substances in mixtures?
- that a mixture of two or more solutes which are soluble in a
particular solvent can be separated and identified by chromatography
- how to separate the different coloured compounds in
an ink mixture on blotting or filter paper, using a wick of the paper
dipped into the solvent (water).
- why do different coloured ink solids travel different
distances?
- use particle ideas to explain how chromatography works
- find out at home whether food or sweet
colourings, inks in felt-tip pens or markers are single dyes or mixtures
of dye.
- how chromatography can be used to compare mixtures of solutes
- how scientists use evidence from chromatography
- forensic science, medical analysis
- chromatography can be used with non-coloured
solutes - but you need to make the different solutes 'show up' in some way
eg add a chemical that makes them coloured or shine on ultra-violet light to
make them 'glow'
Is there a limit to the amount of solid that will dissolve in a liquid?
- when a solid is added to a liquid, eventually no more will
dissolve (a saturated solution) - there is limit to how much can dissolve in a particular
volume of solvent - how can you tell no more dissolves?
- that different masses of different solids dissolve in the same
volume of a particular solvent
- that solids can dissolve in liquids other than water
- state that some solids dissolve more in some liquids than others
- different solvents, different solubility
What else affects solubility?
- that many solutes are more soluble at higher temperatures
- you can use tables of data to calculate quantities of material to use
(see examples)
- to make comparisons, identify patterns and make predictions from
graphs (see examples)
- cooling a saturated solution, eg of benzoic acid, which forms crystals as it cools.
- state that a saturated solution has been formed when crystals
appear
- state the solubility at a particular temperature,
eg at 70°C,
3g of the solid dissolved in 100g of water
- it is important to draw the
distinction between dissolving in terms of ‘how much’ and ‘how fast’.
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