Topic 9 – Reactions of Acids – Learning Outcomes
General Level
o State that neutralisation is the reaction of acids with neutralisers
o Give everyday examples of neutralisation, including: reducing acidity in soil
by adding lime, the use of lime to reduce acidity in lakes caused by rain,
treatment of acid indigestion
o State that neutralisation moves the pH of an acid toward 7
o State that the reaction of acids with alkalis is an example of neutralisation
o State that neutralisation moves the pH of an alkali towards 7
o State that the reaction of H+(aq) to form water is an example of
neutralisation
o Name the products formed in the reaction of a neutraliser with dilute
hydrochloric, nitric or sulphuric acid
o State that an acid reacts with a metal carbonate to give off carbon dioxide
o Explain the effect of acid rain on buildings and carbonate rocks
o State that an acid reacts with some metals to give off hydrogen gas
o State that in the reaction with metals, hydrogen ions form hydrogen
molecules
o Name the products formed when dilute hydrochloric or sulphuric acid reacts
with a metal
o Explain the effect of acid rain on structures made from iron
o State that precipitation is the reaction of two solutions to form an insoluble
product called a precipitate
o Name the insoluble product formed by the reaction of two solutions
Credit Level
o State that the reaction of hydrogen ions with hydroxide ions form water
o Define a salt as a substance in which the hydrogen ion of an acid has been
replaced by a metal ion (or the ammonium ion).
o State that the reaction of hydrogen ions and carbonate ions forms water
and carbon dioxide
o Explain why, in the preparation of a given salt, it is often easier to use an
insoluble metal carbonate or metal oxide as the neutraliser
o Define a base as a substance, which neutralizes an acid
o State that bases which dissolve in water form alkalis
o State that insoluble salts can be formed by precipitation
o Carry out calculations to find the concentration of acids/alkalis from
volumetric titration.
Topic 9 Notes
Neutralisation is the reaction of acids with bases to make neutral
compounds. A base is any substance that will neutralise an acid.
When we put a base into water it forms an alkali.
If the correct volume of alkali is used, they can be used to
neutralise acids, but if too much is added then we can make
something alkaline instead of something neutral. When we
neutralise an acid the pH increases towards 7. When we
neutralise an alkali the pH decreases towards 7.
Acids all contain the H+ ion. When an acid is neutralised this H+
ion usually forms water. When an acid and an alkali react
together they form water. This is because the H+ ion of the acid
joins with the OH- ion of the alkali to make water (H2O).
Everyday Examples of Neutralisation
There are examples in everyday life where acid is required to be
neutralised:
Indigestion is caused by too much acid in the stomach and can be
neutralised with tablets.
Acid rain can lead to soil becoming too acidic, farmers can add
lime (calcium carbonate) to the soil to help neutralise the acid.
Lime can also be used to reduce the acidity of lake water.
Acids and Bases
When acids react with a base they form a number of products,
one is a salt and the rest depend on what is being used in the
reaction. A salt is formed when the hydrogen ion of the acid is
replaced by the metal ion of the base. The salt formed depends
on the reactants:
Sulphuric acid makes sulphate salts
Nitric acid makes nitrate salts
Hydrochloric acid makes chloride salts
There are three main bases we have to know about.
1. When an acid reacts with a metal hydroxide we form a salt
and water. Some examples are:
Sulphuric acid + sodium hydroxide  water + sodium sulphate
Nitric acid + magnesium hydroxide water + magnesium nitrate
Hydrochloric acid + lithium hydroxidewater + lithium chloride
2. When an acid reacts with a metal carbonate we form a salt,
water and carbon dioxide. An example is:
Sulphuric + Calcium  Calcium sulphate + Water + Carbon
Acid
Carbonate
Dioxide
We form water and carbon dioxide from the hydrogen ions
reacting with the carbonate ions. We can test for carbon
dioxide by collecting the gas and seeing if it turns lime water
milky.
This is one of the problems with acid rain. When acidic rain
comes into contact with carbonate buildings, the brick work
starts to react and can be damaged.
3. When an acid reacts with a metal we form a salt and
hydrogen gas. An example is:
Hydrochloric acid + Sodium  Sodium chloride + Hydrogen
In this reaction the hydrogen ions in the acid react with each
other to form hydrogen molecules. We can test for the
presence of hydrogen by collecting the gas and testing that it
burns with a pop.
This is another problem with acid rain. When the acid rain
comes into with metal it can react and cause the metal to
weaken.
Making Salts
Reacting acids with bases is a good method for making specific
salts. This is easier to do by using a powered base such as a
metal carbonate powder with the acid. An example is the
practical technique, preparation of a salt by neutralisation. In
this reaction a given volume of acid is reacted with powdered
copper carbonate. This meant we could add excess (more than
we actually needed) powered carbonate to make sure all the
acid was neutralised. We could then filter the extra powder
off.
Salts can also be made by mixing two ionic solutions together.
When this happens the metal ions in each solution swap and we
can use this to make salts as long as one of the salts formed is
insoluble. Here is an example:
Copper
+ Lithium
 Copper
+ Lithium
Sulphate(aq) Carbonate(aq)
Carbonate(s) Sulphate(aq)
We can see that with these two liquids reacting that they
metals have swapped places with each other. By checking page
5 of the data book we can see the copper sulphate is insoluble
(s) so makes a solid and lithium sulphate is soluble so remains in
solution (aq). We call this type of reaction precipitation as we
are making a solid from two liquids. This is how we make
insoluble salts.
Titrations
For this topic you also need to be able to understand titration
reactions and do calculations based on titration results. For
the calculation see the calculation sheet.
The actual experiment is carried out using a burette and
pipette. A pipette is used to accurately measure out a volume
of alkali. An indicator is then added to this that will change
colour once the alkali has been neutralised.
The alkali is placed in a flask under the burette filled with
acid. Acid is then added carefully until the alkali has been
neutralised. We repeat this experiment until we have two
results within 0.2cm3 of each other and then we use the
average of those two results. This makes sure we have
accurate results.
Past Papers
07 General: 9bii, 11d, 11e
07 Credit: 6a, 6b, 8
08 General: 7a, 11a, 15bii, 20b
08 Credit: 5a, 8
09 General: 4b, 4d, 6b, 18c
09 Credit: 4a, 4b, 6a, 13a