s1 mix it up! summary notes - larbert high school
TRANSCRIPT
S1 Mix it Up! Summary Notes
Solubility - Mixtures
1 – To develop our understanding of particles in substances.
A pure substance contains only one type of particle.
We can see in this extremely close up photo of gold
that all the particles are identical so gold can be
considered a pure substance.
A substance may also contain a mixture of
particles, just like different sweets can be found
together in a mixture. This is not considered a
pure substance as not all the particles are
identical.
The diagram above shows two different substances being added
together to form a mixture. Notice that..
..although they are mixed together they have not chemically joined.
..the smaller particles are able to fit in the spaces between the
larger ones.
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Solubility – Investigating Solubility
2 – To investigate solubility and identify the definitions of solute, solvent and solution.
When you add sugar to tea it gives it a sweet taste. You can’t see the sugar anymore but it is still there as you can taste it. The sugar has dissolved. When a substance dissolves, the particles mix with the particles of the liquid. As sugar dissolves in water to make a solution, sugar is said to be soluble.
In a solution, the substance that is dissolved is called the solute. The solvent is the substance which does the dissolving. When the solute dissolves in the solvent, the mixture produced is called a solution.
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A solution containing a lot of sugar is called a concentrated solution. A solution containing a lot of solvent is called a dilute solution.
If you put lots of sugar in your cup of tea or coffee, it may not all dissolve. If the solution cannot dissolve more solute it is called a saturated solution. If a substance is not soluble (it doesn’t mix) it is
insoluble.
Solubility – Investigating Separation Techniques
3 – To investigate separation techniques.
The individual substances in a mixture can be separated using different
methods, depending on the type of mixture.
Filtration – Separating an Insoluble Solid from a Liquid
If a substance does not dissolve in a solvent, we say that it is insoluble. For example, sand does not dissolve in water – it is insoluble.
Filtration is a method for separating an insoluble solid from a liquid.
When a mixture of sand and water is filtered:
the sand stays behind in the filter paper (it becomes the residue)
the water passes through the filter paper (it becomes the filtrate)
Evaporation – Separating a Soluble Solid from a Liquid
Evaporation can be used to
separate a soluble solid from a
liquid. For example, salt is soluble
in water. During evaporation, the
water evaporates away leaving
salt behind.
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Distillation – Separating a Solvent from a Solution
Distillation is a method for separating the solvent from a solution.
For example, water can be
separated from a salt solution
by simple distillation.
This method works because
water has a much lower boiling
point than salt. When the
solution is heated, the water
evaporates.
It is then cooled and condensed
into a separate container. The
salt does not evaporate and so
it stays behind.
This process can also be used to separate a mixture of liquids with
different boiling points.
Acids & Alkalis - The pH scale
4 – To develop our understanding of the pH scale
Acids and alkalis are very common substances in a science lab and at
home. The pH scale measures the acidity and alkalinity of a substance
in a solution. (The substances must be dissolved in water)
There are different pieces of equipment for measuring the pH of a
substance.
The pH meter gives a digital value between 0 and 14 which tells us how
acidic or alkaline a substance is.
The pH paper and universal indicator will show a colour when tested
with a substance. This can then be compared with the pH scale to
determine how acidic or alkaline the substance is.
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pH meter pH paper Universal indicator
Acids & Alkalis - Measuring pH of a substance
5 – To explore the uses of acids and alkalis in everyday life
The diagram below shows how we can easily measure the pH of any
substance with a piece of pH paper.
Below are some examples of everyday acids and alkalis and their pH:
Name of Substance Laboratory or
Household
Colour of pH
paper
pH
number
Acid, Alkali
or Neutral
hydrochloric acid lab red 1 acid
sodium hydroxide lab blue 14 alkali
vinegar house red 3 acid
baking soda house blue 9 alkali
nitric acid lab red 1 acid
ammonia solution lab blue 11 alkali
pure water house green 7 neutral
soda water house red 5 acid
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Substance to be
tested
dimple
tile
small piece of
pH paper
dishwasher powder house blue 10 alkali
lime water lab blue 9 alkali
cola house red 5 acid
lemon juice house red 4 acid
sulphuric acid lab red 1 acid
oven cleaner house blue 13 alkali
lemonade house red 4 acid
salt water house green 7 neutral
bleach house blue 13 alkali
Common Household Acids Common Household Alkalis
vinegar dishwasher powder
lemon juice oven cleaner
cola bleach
Laboratory Acids Laboratory Alkalis
hydrochloric acid sodium hydroxide
sulphuric acid ammonia solution
nitric acid calcium hydroxide
Acids & Alkalis - Dilution of acids
6 – To investigate the effect of dilution on acids and alkalis
A concentrated acidic solution is one that contains a lot of acid
compared with water. A dilute solution contains more water than acid.
Think of diluting orange juice:-
More orange and less water = concentrated solution Less orange and more water = diluted solution
Diluting an acid by adding more water increases the pH of the solution
towards 7 making it less acidic.
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As the acid is diluted the pH increases towards 7
Diluting an alkali by adding more water decreases the pH of the
solution towards 7 making it less alkaline
It is not possible to dilute an acid so that its pH increases to greater than
7 nor an alkali so that its pH decreases below 7. This is because we are
diluting them with water which is a neutral substance (with a pH of 7) so
adding more and more water will simply maintain the pH of the diluted
acid or alkali at 7.
Acids & Alkalis - Neutralisation
7 – To investigate the reactions of acids and why these reactions are useful. 8 – To investigate how changing certain variables affects the rate of the reaction between an acid and calcium carbonate
Acids and alkalis neutralise each other to form a salt and water.
Remember that the acid has a low pH and the alkali a high pH, but when
they are mixed in precise quantities they form water (a neutral
substance) plus salt.
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As the alkali is diluted the pH decreases towards 7
When performing a neutralisation experiment it is important not to add
too much alkali to the acid as the pH will increase beyond 7 creating an
alkaline solution.
Remember that neutralisation is not the same as dilution. In dilution
water is added to the acid so the pH of the solution cannot increase
above 7 but in neutralisation it is an alkali that is being added so it is
quite easy to go beyond 7 and produce a high pH alkali.
Everyday examples of neutralisation:
Alkali
Indigestion tablets help with
heartburn by neutralising
stomach acid
Neutralisation with indigestion powder
Acids and alkalis neutralise each other to form a salt and water. Other
substances also neutralise acids to form a salt.
This time we see that the red hydrochloric acid turns green as it is
neutralised but we also notice that a gas is given off.
Indigestion powder is a form of metal carbonate which means it will give
off carbon dioxide gas as well as salt and water during neutralisation.
spatula stirring rod
10cm3 hydrochloric acid + 3
drops of universal indicator
Indigestion
powder In this experiment,
indigestion powder is
used to neutralise
hydrochloric acid just like
an alkali neutralises an
acid.
Toothpaste neutralises acid from food and so helps to prevent tooth decay
Acid Rain
9 – To develop our understanding of the causes of and resultant problems with acid rain. 10 – To investigate how we can reduce acid rain.
Non-metal elements can react with air or oxygen to form compounds
called oxides.
carbon + oxygen carbon dioxide
sulphur + oxygen sulphur dioxide
nitrogen + oxygen nitrogen dioxide
Non-metal oxides which can dissolve in water (like those above)
produce acids.
e.g. Sulphur dioxide dissolves in water to produce sulphuric acid
Nitrogen dioxide dissolves in water to produce nitric acid
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Acid Rain is an environmental problem which can:
damage buildings made from carbonate rocks (e.g. marble)
corrode metals structures made of iron and steel (e.g.
bridges)
affect plant life by changing the pH of soil (e.g. less crops
grown)
affect animal life by changing the pH of rivers/lakes (e.g. kills
fish)
Acid rain could be reduced if the gases that cause acid rain were
reduced:
Carbon dioxide is released when fossil fuels like coal, petrol and
gas are burned
If we burn less fossil fuels, then less carbon dioxide will
be released
Sulphur dioxide is released when fossil fuels like coal are burned
Use low-sulphur fuels instead of high sulphur fuels
Remove sulphur dioxide fumes before release into
atmosphere
Nitrogen dioxide is produced in car engines by the sparking of air
with petrol to set the petrol on fire.
Fit catalytic converters to cars to remove nitrogen
dioxide from car exhaust fumes.