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Similar to KS3 Acids and Alkalis.pptx
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KS3 Acids and Alkalis.pptx
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What is an acid?
Acids are a group of soluble chemicals.
What do you know about acids?
Are all acids dangerous?
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What is a weak acid?
Some acids are found in everyday items such as food and
drink, and skincare products.
It is safe to handle these acids, and in some cases even to
taste them! These acids are known as weak acids.
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What is a strong acid?
Some acids, like those found in the laboratory or a car
battery, are too dangerous to taste or touch.
These acids are said
to be corrosive as
they can damage
other materials by
wearing them away.
What safety precautions should you take when handling a
strong acid?
These are strong acids.
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The Acid Bath Murderer
Concentrated acids can completely dissolve skin and bones.
In the 1940s, an Englishman called John Haigh murdered six
people, and disposed of each of the bodies by dissolving them
in sulfuric acid for two days.
Without the bodies as evidence Haigh
thought he would get away with the
crimes, but a pathologist found human
fat, pieces of bone, gall stones and
false teeth, which had resisted the acid.
John Haigh was found guilty of the murders and sentenced to
death by hanging in 1949.
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What is an alkali?
Alkalis are substances that are chemically the opposite
of acids.
Weak alkalis are found in soaps and other
cleaning materials. They are also used in
antacids to treat indigestion.
It is safe to handle these
alkalis, which often feel soapy.
These alkalis are weak
alkalis.
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What is a strong alkali?
Some alkalis, like those used
in laboratories, or in cleaning
materials such as bleach, are
too dangerous to touch.
What safety precautions
should you take when
handling a strong alkali?
These alkalis are said to be
caustic because they can
burn skin, and damage other
materials.
These are strong alkalis.
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What effect do alkalis have on our skin?
Many people suffer from eczema, a condition which can make
the skin itchy and sore.
Sometimes this is caused by
an allergic reaction to soap
or other cleaning materials.
Which chemicals in soap do
you think might cause the
allergic reaction?
How could you find
out what is causing
the allergic reaction?
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What is a neutral substance?
Neutral substances are neither acidic nor alkaline.
Pure water is a neutral substance.
What safety precautions should
you take when handling a
neutral substance?
Saltwater, milk, saliva and
blood may actually be slightly
acidic or alkaline, but are all
very close to neutral.
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Acids, alkalis and plants
Some flowers change colour depending on whether they are
growing in acidic or alkaline soil. Hydrangeas grow blue
flowers in an acidic soil, but pink flowers in an alkaline soil.
The flowers contain compounds called anthocyanins, which
act as indicators.
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What is an indicator?
An indicator is a chemical that turns a different colour
depending on whether it is added to an acid or an alkali.
Litmus is a commonly used indicator. It can be added to filter
paper, or used as a liquid. Litmus is made from lichen, which
grows on stone and rock.
Litmus can be blue or red.
Blue litmus turns red under
acidic conditions (< pH 4.5),
and red litmus turns blue under
alkaline conditions (> pH 8.3).
What colour do you think litmus
is under neutral conditions?
acid
alkali
neutral
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What is universal indicator?
Universal indicator has a range of colours that show how
weak or strong the acid or alkali is.
What is the colour for a strong alkali?
What is the colour for a weak acid?
Universal indicator is made from a mixture of indicators.
Why do you think it is more useful than litmus?
weak alkali
weak acid
strong acid neutral strong alkali
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What is the pH scale?
The strength of an acid or alkali is measured by the pH scale.
Each universal indicator colour is given a pH value.
Universal indicator can tell you the pH of a solution.
What is the pH of a strong alkali?
What is the pH of a weak acid?
1 2 3 4 5 6 7 8 9 10 11 12 13 14
strong acid neutral strong alkali
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Soil pH
Different soils have different pH levels. This is because
they are made up of different rocks, and so contain
different chemicals.
The pH of soil affects the
availability of nutrients,
and plants prefer to grow
in soils of a certain pH.
How could you check the pH of the soil in your garden?
For example, strawberries
grow best in acidic soil,
and plums grow best in
alkaline soil.
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Changing soil pH
If soil is too acidic to grow certain crops, lime can be added.
Lime is an alkali called calcium oxide.
What effect does lime have on the pH of soil?
