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Doc Brown's Chemistry
KS3
SCIENCE-Chemistry QCA
Unit 8F Compounds and mixtures
KS3 Quizzes or task sheets based on this summary: four word-fill worksheets * multiple
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8F
Compounds and mixtures
 QCA 8F "Compounds and mixtures"
Multiple Choice Questions for Science revision
on comparing the properties and differences between elements, compounds
and mixtures, melting and boiling points, idea of pure/impure.
 8Fwf1-5 five
handy linked word-fill
worksheets * 8Fwf2 * 8Fwf3 *
8Fwf4 *
8Fwf5 *
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 quiz
or drag-drop version-printout
The
8F crossword and word-fill
In this unit you will learn to ..
- distinguish between elements and compounds and how they are represented
by symbols and formulae - these show the relative numbers and types of
atom present
- recognise chemical change as a process in which atoms join together in
new ways
- distinguish between compounds and mixtures
- distinguish between chemical reactions in which new compounds are formed
and the formation of mixtures
- investigate temperature changes as liquids cool
- use line graphs and choose appropriate scales
for eg time, temperature or mass data.
- distinguish between elements, compounds and mixtures in
terms of the particles they contain
- name and describe some common mixtures and
use knowledge about separation techniques to suggest how they might be separated
- identify melting and boiling points as the fixed temperatures at
which elements and compounds change state and use the particle model to explain
changes of state
- know mixtures do not change state at fixed temperatures
Its handy if you ...
- can name some elements
- know that there are approximately 100 elements which are the building
blocks for all materials
- know that elements are composed of tiny particles called atoms
- know that compounds are formed when atoms of different elements join
- have explored a number of chemical reactions
- have made and separated mixtures
Some important words for you to understand, use and spell
correctly
- words with precise scientific meaning, eg element, compound, mixture,
atom, composition, pure
- names of compounds, eg sodium carbonate, calcium chloride,
hydrochloric acid
How are elements and compounds different?
- that elements contain only one kind of atom
- that compounds contain more than one kind of atom
chemically bonded (joined) together
- that formulae indicate the (relative) numbers of atoms in a
compound
- distinguish between elements and compounds
in terms of names and symbolic formulae
How do compounds differ from the elements from which they are made?
- that compounds contain elements that are chemically combined
- that the properties of a compound are different from those of the
elements from which it is made
- that a compound always contains the same elements in fixed
proportions and relate this to interpreting formulae for compounds in terms of the relative numbers
of atoms of different elements
- effect of heating a
mixture of iron and sulphur powders in ignition tubes - a red
glow and no yellow powder left after their tube has cooled - what
evidence for suggesting chemical change - to extract the contents -
does it still contains a mixture or if a new chemical
(compound) has been made? write a word, picture or symbol equations for the
reaction
- show that the compound iron sulphide behaves differently
from its constituent elements sulphur and iron, eg by adding a small
amount of dilute acid to both and observing the differences in the way
the mixture behaves compared to the compound.
- names of compounds eg water,
carbon dioxide, copper carbonate - compare the compounds with the elements from which they are
made - describe differences between compounds and the elements from
which they are made
- consider the formulae of some of the
oxides made in unit 8E ‘Atoms and elements’, eg magnesium, sodium
and aluminium oxides, and the fact that compounds are made from elements in fixed
proportions - pictures showing particles in examples of elements, compounds and various
mixtures of elements and/or compounds
Do compounds react chemically?
- that compounds can react chemically
- observe a number of test tube chemical reactions
in which visible changes occur, eg mixing sodium carbonate solution and iron(II) chloride
solution; adding dilute hydrochloric acid to solid magnesium carbonate; adding dilute ammonia solution to copper sulphate solution;
heating sucrose
- identify appropriate indications of chemical reactions
- state that chemical reactions took place between the compounds
- note that some physical changes also
involve colour changes and gas evolution, and that a chemical reaction
is distinguished by changes in the ways the atoms are bonded together.
Are there other sorts of material besides elements and compounds?
- reminder about differences between compounds and mixtures
eg in unit 7H ‘Solutions’
and show them examples of mixtures they may have encountered, eg iron
and sulphur, chalk in water, seawater, air, soil, rocks, ink, shaving
foam
- and drawing diagrams to illustrate the particles in elements
and compounds and extending this to mixtures
-
criteria for deciding whether something is a mixture or not
- the idea that compounds can be represented by a formula whereas mixtures
vary in composition and have no fixed formula, eg by showing samples of compounds together with
molecule models, and contrasting these with samples of mineral water
which is a mixture
- the meaning of ‘pure’ when
applied to a material, eg What is ‘pure’ orange juice? What is
‘pure’ water?
- what is meant by ‘pure’ and ‘impure’
and link to eg the illustrations of elements, compounds and mixtures
made earlier in the activity
- name some everyday mixtures, eg air
(gases), seawater and mineral water (which are both liquid water
containing dissolved gases and solids)
- identify that mixtures (eg above) can vary in composition
and can be separated (eg in unit 7H ‘Solutions’)
- the idea of rocks as mixtures is explored more fully in unit 8G
‘Rocks and weathering’ and unit 8H ‘The rock cycle’ but handy to use the same rock samples in this
activity
- name the main gases present in air and give approximate
proportions of these (the particles maybe element atoms, element
molecules and compound molecules)
- explain clearly how air can be
separated into its components - if cooled enough under pressure it will
liquefy
- describe clearly some uses of the components of air
- related work on photosynthesis and respiration in unit 8B
‘Respiration’, unit 9B ‘Fit and healthy’ and unit 9C ‘Plants
and photosynthesis’, and air pollution in unit 9G ‘Environmental chemistry’.
- that elements and compounds melt and boil at particular
temperatures and the temperatures are characteristic of these substances
(note boiling point is always above the melting point!)
- that mixtures do not melt or boil at fixed temperatures
- look back at work on elements in unit
8E ‘Atoms and elements’ and to identify boiling points and melting
points of some of these elements - note very
high temperatures at which some metals melt
-
demonstration of the differences in the boiling point of tap water and
salt solution which illustrates that mixtures do not have fixed
melting or boiling points and they are different than the values for
pure substances
- describe how the melting point or boiling point of a mixture
varies with composition
- a temperature line was constructed in unit 8I ‘Heating
and cooling’ - can investigate how
temperature changes as they cool (surrounded by an ice/salt mixture)
liquids eg pure and impure stearic acid.
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