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School Chemistry: Describing the techniques of filtration, evaporation, crystallization
Mixture separation methods: FILTRATION, EVAPORATION, CRYSTALLISATION, DRYING and DECANTATION
Doc Brown's chemistry revision notes: GCSE chemistry, IGCSE chemistry, O level & ~US grades 9-10 school science courses or equivalent for ~14-16 year old students of chemistry METHODS OF SEPARATING MIXTURES using FILTRATION, EVAPORATION, CRYSTALLISATION, DECANTATION Key words explained: insoluble, soluble, solvent, solute, saturated solution, PART 2.4 Methods of separating mixtures are described e.g. filtration, evaporation, crystallisation, decantation, purifying substances by filtration and crystallisation Part 1 Definitions in Chemistry, Elements, Compounds & Mixture pictures & Physical & Chemical Changes Part 2 Methods of Separating Mixtures of substances Part 3 How to write equations, work out formula and name compounds Alphabetical list of KEYWORDS for Parts 1-3: atom * balancing equations (work your way down the section carefully) * centrifuges/centrifuging * chemical reaction/change * chromatography (paper/thin layer) * compound * covalency * crystallisation * decanting/decantation * displayed formula * distillation (simple or fractional) * element * equations * evaporation * filtration * formula * gas chromatography * impure/pure * insoluble * ionic equations * ionic valence * iron-sulphur separation and heating experiment * magnet * mixture * molecule * naming compounds and ions * particle pictures of elements/compounds/mixtures * physical change * precipitation * products * pure substance * purification * reactants * sand/salt separation * separating funnel * separating mixtures * soluble/solution/solvent/solute * solvent extraction * symbols (for elements, formula, in equations) * state symbols * working out formulae * [SEARCH BOX] and [Main INDEX] Revision notes on apparatus needed for filtration, crystallisation, drying crystals, evaporation techniques all explained with diagrams for help when revising for AQA GCSE 9-1 chemistry, Edexcel GCSE 9-1 chemistry, OCR GCSE 9-1 gateway science, OCR GCSE 9-1 21st century science GCSE 9-1 chemistry practice examination questions |
2.4 Four techniques used in particular
separation & purification procedures Filtration, evaporation, crystallisation and drying are four techniques used in the isolation and purification of a solid product from a chemical reaction e.g. How can we separate a mixture of sand and salt? or, how do we separate a salt from a salt preparation? What do the words solvent, solute, solution, soluble, insoluble and solubility mean? solvent: the liquid that dissolves something, often water - very useful because it dissolves many things solute: the substance that dissolves in the solvent solution: the homogenous mixture of the solute and solvent? soluble: the property of substance that allows it to dissolve in a solvent insoluble: the property of substance that stops it dissolving in a solvent solubility: how soluble a substance is in a solvent (often water) Remember, in all the physical separation processes of filtration, evaporation and crystallisation, no chemical reactions are involved, so no new substances are made. |
FILTRATION, EVAPORATION, CRYSTALLISATION and DRYING
procedures All these terms are explained and the techniques described in detail, and remember,
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Filtration works because any tiny dissolved molecule particles OR the liquid molecules are too small to be filtered and pass through the filter paper with the equally tiny water molecules. BUT, any insoluble 'non-dissolved' solid particles are too big to go through and are trapped of 'filtered' out by e.g. a filter paper, but it can be any form of VERY fine mesh.
Here filtration is used in STEP 3 to separate a desired insoluble compound from the original liquid reaction mixture.
Evaporation means a liquid changing to a gas or vapour. In a mixture separation procedure, it is the removal of most of the liquid from a solution, usually to cause crystallisation to leave solid crystals in the evaporating dish - but you should not heat some salts to complete dryness - see copper sulfate note.
Crystallisation can mean a liquid substance changing to its solid form. However, the term usually means what happens when the liquid from a solution has evaporated to a point beyond the solubility limit of the dissolved solid. Then solid crystals will 'grow' out of the solution because the solution is too concentrated for all the solid to remain dissolved at that temperature.
Drying may be the final stage in the chemical preparation of a product and here in this context it means removing the last traces of liquid (e.g. the solvent) from the solid product (which may be a powder or nice crystals).
These separation methods are involved in e.g. (1) separation of a sand and salt mixture or (2) salt preparations
Here the solvent is water, but other mixtures can be separated using the same sequence of procedures using a different solvent. e.g. copper and sulphur can be separated using an organic solvent like tetrachloromethane which will dissolve the sulphur (hazardous chemical solvent) and you can filter off the copper.
Lawn sand is a mixture of sharps sand and soluble
ammonium sulfate. You can separate out the sand and eventually
crystallise the ammonium sulfate in exactly the same way as impure salt,
described above.
(2b)
The technique of solvent extraction
involves using a liquid to dissolve a solid to separate it from a
mixture (e.g. in purifying salt in the experiment described above.
AND
in these separation procedures there always loss of product I'm afraid there is a bit more to it than beakers,
filter funnels etc.!!!
Reminders of some important words-phrases to do
with the above procedures.
A
solvent is a liquid that
dissolves the substance, in doing so it must completely break the bonds
between the particles in the substance being dissolved (the solute).
This enables the solute particles to fully mix with the solvent.
The solute is the substance that
is being dissolved in a solvent. A solid may dissolve in one
liquid (soluble) but not in another (insoluble).
A solution is a mixture of a
liquid with something dissolved in it. If you evaporate the solvent
away, you should be left with the 'dry' solid solute you dissolve in the
first place.
Soluble
Insoluble
Solubility
See alcohols and
esters for further
discussions of solvents and solutes including the theory of
intermolecular forces.
See how these methods are
used in making salts methods (a)-(c) % reaction yield
& reasons for loss of product *
atom economy *
% purity of a product
2.4d DECANTATION Decanting is
the simplest possible way of separating a liquid (pure or a solution)
from an insoluble solid which has a density greater than water (i.e. >
1.0 g/cm3). The solid-liquid mixture is allowed to stand e.g. in a
beaker, until all the solid settles out to the bottom of the container. Then the liquid is carefully poured off to leave the insoluble solid
behind. However it is inefficient e.g. a small amount of liquid is
always left in the solid residue and very fine solid particles take some
time to settle out and any disturbance of the liquid can mix them in
with the liquid being poured off. Wine may be served in a decanter to
leave the undesirable solids behind - no good for bits of cork though,
they float! Revision notes on apparatus needed for
filtration, crystallisation, drying crystals, evaporation techniques all
explained with diagrams for help when revising for
AQA GCSE 9-1 chemistry, Edexcel GCSE 9-1 chemistry, OCR GCSE 9-1 gateway science, OCR
GCSE 9-1 21st century science GCSE 9-1 chemistry
practice examination questions |
See other web page for:
QUESTIONS: GCSE balancing and completing equation exercises:
(1)
GCSE 'name and formula' of a compound quizzes
(1)
information on separation by filtration
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phrases: what is filtration? what do we use filtration for? what can we
separate using a filter paper? Why does salt particles in solution go
through a filter paper? what are the uses of filtration? what does
filtration do? what do we mean by soluble? what do we mean by insoluble?
what does it mean if a substance is described as insoluble? how do we
carry out a filtration procedure? what do we use filtration for?
what do we use evaporation for? how do we crystallise a salt from
solution? how do we do a crystallisation? what is crystallization? give
an examples of crystallisation? what is a solvent? what is a solute? why
is water a good solvent? what is a solution? what do we mean by soluble?
what do we mean by insoluble? what do we mean by solubility? how do you
do a crystallisation? how can you dry salt crystals? what is a
desiccator? what is decantation? what is decantation used for?
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