Introducing Science Summary Sheet
Acids in the laboratory
Dilute acids
You will have used some dilute acids at school, such as hydrochloric acid,
sulphuric acid and nitric acid. Their bottles are labelled with the warning symbol
for 'irritant'.
This means that if any of them makes contact with your skin, it will become red or blistered. You must wash off
any spills with plenty of water, otherwise your skin will soon feel as if it is burning.
Concentrated acids
You are unlikely to have used concentrated acids but your teacher might have
shown you some experiments with them. This is because concentrated acids are
corrosive. They can attack metals and destroy skin if spilled.
Acids in the home
Laboratory acids are far too dangerous to taste, but you will have swallowed some dilute weak acids. Acids have a
sour taste, like vinegar, which contains ethanoic acid, and lemons, which contain citric acid. These are safe to use
in food, but they can still hurt if they get into a cut or into your eyes.
Other acids you will find at home are carbonic acid in fizzy drinks, tannic acid in tea and ascorbic acid which is
vitamin C, found in fruit and vegetables.
Bases and alkalis
Bases v alkalis
Bases are substances that react with acids and neutralise them. They are usually metal oxides, metal hydroxides,
metal carbonates or metal hydrogen carbonates. Many bases are insoluble - they do not dissolve in water. If a base
does dissolve in water, we call it an alkali.
Here are two examples:

Copper oxide is a base because it will react with acids and neutralise them, but it is not
an alkali because it does not dissolve in water.

Sodium hydroxide is a base because it will react with acids and neutralise them. It's
also an alkali because it dissolves in water.
Introducing Science Summary Sheet
Bases in the laboratory
You will have used some strong bases and alkalis at school, such as sodium hydroxide solution. Like acids,
their bottles are labelled with the warning symbol for 'irritant'. This means that they will make your skin
red or blistered unless you wash off any spills with plenty of water.
Alkalis feel soapy when they get on your skin, so it is easy to tell when you have had an accident and must
wash your hands.
SOLID
Concentrated alkalis are corrosive. They can attack metals and destroy skin if spilled. They are just as
• Solids are made up of particles that are very close
dangerous as concentrated acids, but many people do not realise this.
together and are held tightly together by strong
bonds.
Bases in the home
• Solids cannot be squashed, do not flow, have
Bases react with oils and fats, so they are often useda in
strong
household
cleaners.
Drain
cleaners
and oven
fixed
shape
and volume,
and are
dense
(are heavy
cleaners usually contain sodium hydroxide for example.
ammonia
is also commonly
used of
in cleaners.
forAnd
their
size). (Volume
is the amount
space
Ammonia can be recognised by its choking smell.
something takes up. It is measured in units such as
cubic centimetres (cm3).)
It is wise to wear gloves when using these substances, otherwise they will react with your skin and burn it.
LIQUID
Weak bases and alkalis are found in toothpaste, antacid tablets (to help cure an upset stomach) and baking
• Liquids are made up of particles that are fairly
powder.
close together; the bonds between the particles are
weaker than the bonds in solids. This allows the
Indicators and the pH scale
particles to move past each other.
When an acid is dissolved in water we get an acidic•solution,
alkalis
make alkaline
If and
a have a
Liquids and
cannot
be squashed,
flow solutions.
quite easily
solution is neither acidic nor alkaline we call it neutral.
Purevolume
water is
neutral,
andshape.
so is paraffin.
fixed
but
no fixed
•
Although they are dense, liquids are usually less dense
Indicators are substances that change colour when they are added to acidic or alkaline solutions. You can
than solids.
prepare homemade indicators from red cabbage or beetroot juice - these will help you see if a solution is
acidic or alkaline.
GAS
•
Litmus and universal indicator are two indicators that are commonly used in the laboratory.
Litmus
•
• and blue in alkaline solutions - and it turns purple in
Litmus indicator solution turns red in acidic solutions
neutral solutions.
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Introducing Science Summary Sheet
Universal indicator and the pH scale
Universal indicator is a mixture of several different indicators. Unlike litmus, universal indicator can show
us exactly how strongly acidic or alkaline a solution is. This is measured using the pH scale. The pH scale
runs from pH 0 to pH 14.
Universal indicator has many different colour changes, from red for strong acids to dark purple for strong
bases. In the middle, neutral pH 7 is indicated by green.
Universal indicator shows how acidic or alkaline a solution is
•
These are the important points about the pH scale:

neutral solutions are pH 7 exactly

acidic solutions have pH
• values less than 7

alkaline solutions have pH values more than 7

the closer to pH 0 you•go, the more strongly acidic a solution is

the closer to pH 14 you go, the more strongly alkaline a solution is
A chemical reaction happens if you mix together an acid and a base. The reaction is called neutralisation,
GAS
and a neutral solution is made if you add just the right amount of acid and base together.
•
Using neutralisation
•

Farmers use lime (calcium oxide) to neutralise acid soils.

Your stomach contains•hydrochloric acid, and too much of this causes
indigestion. Antacid tablets contain bases such as magnesium hydroxide and
magnesium carbonate to neutralise the extra acid.

Bee stings are acidic. They can be neutralised using baking powder, which
contains sodium hydrogen carbonate.
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