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Topic 5: Acids, Bases and salts.
Acids contain ________ ions.
Acids are solutions of pure compounds in water. The pure compounds are molecular but in
water the molecules break up to form ions. They always give ______ ions.
Example: Hydrochloric acid gives ___________ and __________ ions
HCl (aq)  _______ (aq) + ______(aq)
The more the ______ ions there are in the solution, the more acidic it is.
Examples of some common acids:
Hydrochloric acid
Sulfuric acid
Nitric acid
Carbonic acid
Ethanoic acid
Methanoic acid
Citric acid
Strong or weak
Where it is found
in the stomach
in acid rain
in acid rain
in soft drinks
in vinegar
ants and nettles
in lemons, oranges
Strong and weak acids
Different acids have different pH values. A typical _________ acid is hydrochloric acid. In
this acid nearly all the acid molecules break up to form ions.
Example: HCl(aq)
 _____(aq)
Example: CH3COOH(aq)
+ _____(aq)
_____________(aq) +
The acid molecule splits up to form ions but at the same time they join again. Carbonic acid,
ethanoic acid, methanoic acid and citric acid are all examples of ___________ acids.
The basicity of an acid
We have seen that it is characteristic of an acid to yield ________ ions in aqueous solution.
The number of ________ ions produced per molecule of the acid is called its ___________.
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Fill in the table below
Hydrochloric acid (HCl)
Sulfuric acid (H2SO4)
Phosphoric acid (H3PO4)
Nitric acid (HNO3)
Ions formed
(H+ and Cl-)
CH3COO-(aq) +
The pH scale
On this scale:
 An acidic solution has a
pH number smaller than
 An alkaline solution has a
pH number greater than
 A neutral solution has a
pH number equal to
 The stronger the acid the
________ the pH.
 The stronger the alkali the
________ the pH.
The table below shows a list of indicators and their colours in acid and alkaline solutions.
Methyl orange
Red litmus
Blue litmus
Methyl red
Colour in a neutral
Colour in an acidic
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Colour in an
alkaline solution
Reaction of the common metals with dilute acids
Dilute hydrochloric acid
Dilute sulfuric acid
of Rapid effervescence in the cold to
form hydrogen. The remaining
solution is colourless.
Rapid effervescence in the cold to
form hydrogen. The remaining
solution is colourless.
of Steady effervescence to liberate
zinc with…
hydrogen in the cold. The remaining
solution is colourless.
Usually slow effervescence to
liberate hydrogen. The remaining
solution is colourless.
iron with..
of Fairly slow effervescence in the cold
to give hydrogen. The remaining
solution is pale green in colour.
Fairly slow effervescence in the cold
to give hydrogen. The remaining
solution is pale green colour.
The bubbles stop when the
reaction is over. The
unreacted magnesium is
then removed by filtering.
dropped in dilute sulfuric
bubbles off.
The filtrate is heated to
evaporate the water. A white
solid is left behind. This solid
is magnesium sulfate.
Write a balanced equation for this reaction: ______________________________________
Note: sodium and potassium are too reactive to be used with any of these acids. These
would explode. On the other hand copper, silver and gold are too unreactive and so they
don’t react with these acids.
When a metal takes the place of hydrogen in an acid, the compound that forms is called a
salt. Therefore usually acids react with metals, forming hydrogen and a salt.
Metal + Acid  Salt + hydrogen
The salts of sulfuric acid are always called ________________.
The salts of hydrochloric acid are called __________________.
The salts of nitric acid are called __________________.
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Action of acids on insoluble bases
In this method a soluble salt is produced from the reaction between an acid and an insoluble
base. However no effervescence is observed as no gas is produced.
Dilute acids will react with insoluble bases to give a salt and a water
Insoluble base (metal oxide or hydroxide) + Acid  Salt + Water
Heat some dilute sulfuric acid in a beaker and add to it, a little at a time some black
copper(II)oxide. Stir gently.
Write down your observations: ________________________________________________
Chemical balanced equation is:
Many salts of metals can be similarly prepared using either an insoluble oxide or an
insoluble hydroxide of the metal with the appropriate acid.
Write balanced chemical equations:
1. zinc oxide + dilute sulfuric acid 
2. zinc hydroxide + dilute sulfuric acid 
3. lead (II)oxide + dilute nitric acid 
4. lead(II) hydroxide + dilute nitric acid 
5. magnesium oxide + dilute hydrochloric acid 
6. magnesium hydroxide + dilute hydrochloric acid 
Actions of acids on carbonates
Carbonate + Acid  salt + water + carbon dioxide
For example when copper (II) carbonate is added in excess to dilute nitric acid,
effervescence is observed due to the production of _______________________.
CuCO3(s) + 2 HNO3(aq)  Cu(NO3)2(aq) + CO2(g) + H2O(l)
Write balanced equation for the following reactions.
1. zinc carbonate + dilute sulfuric acid
2. calcium carbonate + dilute hydrochloric acid
3. lead (II) carbonate + dilute nitric acid
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Note: If the salt produced is insoluble in water, the salt will precipitate on the unchanged
carbonate and stops the reaction. Example, if dilute sulphuric acid is added to calcium
carbonate, there is rapid effervescence for a few seconds, but the reaction quickly stops.
CaCO3(s) +
H2SO4(aq)  CaSO4(s) + CO2(g) + H2O(l)
The very slightly soluble calcium sulfate precipitates on the calcium carbonate and the
reaction stops.
Action of acids on sulphites
+ acid
 salt + water + sulfur dioxide
When sodium sulphite is warmed with dilute sulphuric acid or dilute hydrochloric acid
effervescence is observed and a gas _______________ is produced.
Na2SO3(aq) + H2SO4(aq)  Na2SO4(aq) + H2O(l) + SO2(g)
Write a balanced equation for the reaction between sodium sulphite and dilute hydrochloric acid.
Bases and alkalis
Definition of a base:
Definition of an alkali:
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Only a few alkalis are known. The common ones are:
ට Sodium hydroxide (NaOH) also known as caustic soda
ට Potassium hydroxide (KOH) also known as caustic potash
ට Calcium hydroxide (Ca(OH)2 also known as lime water
ට Ammonia solution (NH3 (aq))
Strong and weak alkalis
NaOH(aq)  Na+(aq) +
However ammonia solution is a ________ alkali because only some ammonia molecules
form ions in solution.
NH4+(aq) + OH-(aq)
Reaction of alkalis with acids
All alkalis react with acids producing a ___________ and ____________.
This is a solution of
hydrochloric acid.
contains H+ ions and Clions. It will turn blue
litmus _______.
This is a solution of
sodium hydroxide. It
contain Na+ ions and
OH- ions. It will turn red
litmus to ______.
When two solutions are mixed,
H+ & OH- ions join to form water
molecules. The result is a
neutral solution of sodium
chloride, containing Na+ & Clions. It has no effect on litmus.
Write a balanced equation for this reaction.
This reaction is called a __________________ reaction. The alkali has __________ the
acid by removing its H+ ions, and turning them into water.
Reaction of alkalis with ammonium salts.
All the alkalis except ammonia will react with ammonium compounds. The products formed
are salt, water and ammonia.
Ammonium salt + alkali  salt + water + Ammonia
Write a balanced equation for the reaction between ammonium chloride and calcium
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Some useful bases
ට Magnesium hydroxide Mg(OH)2 is found in milk of magnesia. It neutralises excess
stomach acid soothing indigestion.
ට Some alkalis are used as bleaches and as alkaline cleaners. Many kitchen cleaners
are alkalis because they contain ammonia (NH3) or sodium hydroxide (NaOH)
which attack grease.
ට Quicklime (calcium oxide – CaO) and slaked lime (calcium hydroxide – Ca(OH)2
are used to neutralise acid soils.
An alkali can neutralise an acid and destroy its acidity. Let’s look at this reaction.
HCl(aq) +
NaOH(aq)  NaCl(aq) + H2O(l)
 Salt
+ water
H+(aq) + OH-(aq)  H2O(l)
Neutralisation is the formation of water from hydroxide ions (OH- ions) and hydrogen
ions (H+ ions).
Normal salts and acid salts
In this example the acid is hydrochloric acid (HCl). The hydrogen ion (H + ion) was replaced
by a sodium ion (Na+ ion) so that sodium chloride, a salt was formed.
When an acid can produce more than 1 hydrogen ion per molecule (example: H 2SO4 can
produce 2H+ ions per molecule) the replacement of H + ions can occur in stages. Thus one of
the H+ of sulfuric acid may be replaced by one Na+ ion to give Na+ HSO4- (sodium hydrogen
sulfate), after which a second similar reaction may yield (Na +)2SO42- (sodium sulfate Na2SO4)
H+(aq) +
Give the reaction of:
Sodium hydroxide + carbonic acid (H2CO3) 
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Sulfuric acid H2SO4
Carbonic acid H2CO3
Acid Salt
Sodium hydrogen sulfate NaHSO4
Sodium hydrogen carbonate NaHCO 3
Normal Salt
Sodium sulfate Na2SO4
Sodium carbonate Na2CO3
Methods of preparing salts
1. Acid + metal
Some dilute sulfuric acid is
put in a beaker and excess
zinc is added. The zinc
begins to dissolve and
effervescence is observed.
Effervescence stops when all
the acid has been used up.
Some zinc is left unreacted.
___________, which leaves
an aqueous solution of
The solution is heated
to evaporate some of
the water. Then it is left
to cool. Crystals of
___________ start to
Write a balanced equation for this reaction
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2. Acid + insoluble base
Copper(II)oxide is an insoluble base. Although copper will not react with dilute sulfuric acid,
copper(II)oxide will.
Some copper(II)oxide is added
to dilute sulfuric acid. On
warming it dissolves and the
solution turns blue. More is
added until no more dissolves.
copper(II)oxide is removed by
____________. This leaves a
_______________ in water.
The solution is heated to
evaporate some of the
water. Then it is left to cool.
__________ start to form.
Write a balanced equation for this reaction
3. Acid + carbonate
The same method (as in method 2) is used to prepare a salt from a carbonate. This is
because most carbonates are insoluble in water. In this method dilute hydrochloric acid is
added to excess copper(II)carbonate. Effervescence occurs while some unreacted
copper(II)carbonate is left. This is removed by ____________ leaving a green solution of
_____________. The solution is heated to evaporate some of the water. Then it is left to
cool. Crystals of _____________ start to form.
Write a balanced equation for this reaction.
4. Precipitation from two aqueous solutions
For example, insoluble barium sulphate is precipitated when solutions of barium chloride and
magnesium sulphate are mixed.
This is a solution of barium
chloride BaCl2. It contains
barium ions and chloride
This is a solution of
magnesium sulphate,
MgSO4. It contains
magnesium ions and
sulphate ions.
When the two solutions are mixed, the
barium ions and sulfate ions bond
together, because they are strongly
attracted to each other. Solid barium
sulfate precipitates.
Write a balanced equation for this reaction.
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Some useful salts
ට Sodium hydrogen carbonate (NaHCO3) (baking powder) – Is used in the
manufacture of baking powders. Under the action of heat it decomposes and gives
off carbon dioxide which cause the cake to ‘rise’ and so be light. This is why it is
commonly called ‘baking soda’
ට Sodium carbonate (Na2CO3.10H2O) – washing soda is used to soften hard water.
ට Epsom salts (MgSO4.7H2O) – used in medicine as a laxative
ට Gypsum and Plaster of Paris (CaSO4.2H2O) – Gypsum is chiefly employed for the
manufacture of plaster of Paris. This is used for making casts for statues, wall
plasters, and in sugery when you break a bone.
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Laboratory Preparation
Hydrogen can be produced by the reaction of a metal and a dilute acid
Metal + Acid  Salt + Hydrogen
The apparatus is set up as shown below.
Dilute hydrochloric acid was dropped on some pieces of zinc in a flat bottomed flask by
means of a thistle funnel. Effervescence was observed, and the gas produced, that is
____________ was collected over water. __________________ which was formed was left
in the flat bottomed flask.
Write a balanced equation for this reaction.
Test for hydrogen
The following method is a test to see if an unknown gas is hydrogen
1. A wooden splint is lit
2. The wooden splint is plunged into a test tube
containing a small amount of the gas.
3. If the gas is hydrogen, the gas burns with a
Squeaky pop.
Other ways of producing hydrogen:
Hydrogen is the product of other chemical reactions:
1. The reaction of reactive metals and water.
Potassium, sodium and calcium all react with water to produce the ____________ and
_________ gas.
Write a balanced equation for the reaction of sodium with water:
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2. The reaction of metals and steam.
The less reactive metals do not react with water but react with steam to produce the
___________ and __________ gas.
Write a balanced equation for the reaction of aluminium and steam.
Hydrogen as a fuel
Hydrogen combines with oxygen to form water. A mixture of the two gases will explode when
lit. The reactions is:
2H2(g) + O2(g)  2 H2O(l)
The hydrogen and oxygen are stored in tanks in the rockets in liquid form.
Physical properties of hydrogen
ට Hydrogen is an invisible gas, neutral to litmus, not toxic and if pure possesses no
ට Hydrogen is the lightest of all gases and so diffuses very rapidly. It is about 20 times
lighter than air.
ට It is almost insoluble in water.
Chemical properties of hydrogen
1. Reaction with a metal
When a compound is formed between an element and oxygen it is called an __________.
When an element is formed between an element and reactive metals (example: NaH, CaH2,
2 Na(s) + H2(g)  2 NaH(s)
Write a balanced equation for the reaction of magnesium with hydrogen
2. Reaction with non metals
Hydrogen can also react with non metals. Example: it reacts with chlorine to form
_______________________ and with nitrogen to form __________
Write a balance equation for the reaction of hydrogen with chlorine.
Write a balanced equation for the reaction of hydrogen with nitrogen.
3. Reduction of metallic oxides
Hydrogen acts as a reducing agent, by removing oxygen. Copper(II)oxide is reduced to
copper, by heating it in a stream of hydrogen. Hydrogen is oxidised to water.
The reaction taking place is:
CuO(s) +
H2(g)  Cu(s) + H2O(g)
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Hydrogen is unique since it can form H+ and H- ions and it can also share electrons with
other atoms to form covalent compounds.
Hydrogen forms ionic hydrides with metals. Example: NaH, CaH2 and MgH2
Hydrogen forms covalent hydrides with non-metals. Example: HCl and NH3
1. Alongside the names of various chemicals are shown their respective pH values in
aqueous solution.
Potassium hydroxide pH13, hydrogen bromide pH2, calcium hydroxide pH11, sodium
chloride pH7, hydrogen chloride pH2, magnesium hydroxide pH10, citric acid pH4.
Which of these substances is/are:
a) strong acid ?
b) weak acid ?
c) strong alkali ?
d) weak alkali ?
e) neutral substance?
In each case write a chemical equation to show the ion present in solution.
2.a) What makes a weak acid ? Give two examples
b) What makes a strong alkali ? Give two examples
3. Write a chemical equation to represent the neutralisation of sulfuric acid with sodium
4. Write a chemical equation of hydrochloric acid with sodium hydroxide.
5. How can you test for the presence of water ?
6. Explain what this symbol
means ? Give examples.
7. Write balanced chemical equations for the following soluble salt preparations:
a) magnesium + sulfuric acid 
b) calcium carbonate + hydrochloric acid 
c) zinc oxide + hydrochloric acid 
d) potassium hydroxide + nitric acid 
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pH of solution:
Colour of universal indicator:
strong acid
9) The following equation shows the reaction that takes place between an acid and an alkali:
a) Name this type of reaction.
b) Write a word equation that shows the reaction between nitric acid and potassium
c) Write a symbol equation for the same reaction.
10) Complete the following equations:
a) calcium carbonate + nitric acid 
b) sodium carbonate + sulphuric acid 
c) Ethanoic acid + sodium hydroxide 
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