Reactions of acids

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Acids and alkalis
How many examples of acids and alkalis can you spot?

Acids: true or false?

Alkalis: true or false?

Mixing an acid and an alkali
What happens when an acid and an alkali are mixed?
+ 
acid alkali
Mixing an acid and an alkali causes a chemical reaction.
How could you check that a chemical reaction has taken place?

Mixing acids and alkalis

What is neutralization?
The chemical reaction between an acid and an alkali is called
neutralization.
What is the pH value of the mixture of salt and water?
+ 
acid alkali salt + water
The mixture of salt and water is neutral, so its pH is 7.
The chemical reaction between an acid and an alkali can be
written as:
acid + alkali  salt + water

Neutralizing stings
Bee stings are acidic.
Which safe household
substances could you
use to treat a bee sting?
Wasp stings are alkaline.
Which safe household
substances could you
use to treat a wasp sting?

Separating a salt

Making salts
The salt produced by a neutralization reaction depends on
the acid and the alkali used.
Sodium chloride is produced by the reaction between
hydrochloric acid and sodium hydroxide.
sodium
hydroxide
sodium
chloride
+  +
hydrochloric
acid
water
Which acid and which alkali would be needed to make the
salt potassium chloride?
potassium
potassium
+  acid hydroxide
chloride
hydrochloric
+ water

Naming salts
 When an alkali reacts with hydrochloric acid, the salt
produced is a chloride.
 When an alkali reacts with sulfuric acid, the salt produced
is a sulfate.
 When an alkali reacts with nitric acid, the salt produced is
a nitrate.
Which acid would be needed to make these salts?
1. copper nitrate
2. magnesium chloride
3. sodium sulfate

Making salts: word equations
Complete these word equations:
potassium
potassium
+  acid hydroxide
chloride
hydrochloric
+ water
sulfuric acid +  sodium
sodium
hydroxide
sulfate
+ water
nitric acid +  potassium
potassium
hydroxide
nitrate
+ water

Making salts: completing equations

Making salts: symbol equations
Complete these symbol equations:
potassium
hydroxide
potassium
chloride
hydrochloric
acid
+  + water
HCl KOH KCl H2+  + O
potassium
hydroxide
nitric acid +  + water
HNO3 KOH KNO3 H2+  + O
magnesium
hydroxide
potassium
nitrate
magnesium
sulfuric acid +  + water
sulfate
H + 2SO4 Mg(OH)2 Na2SO4 2H2 + O

Balancing equations
When a chemical reaction occurs, it can be described by a
a symbol equation.
The balanced symbol equation for a chemical reaction shows
the ratio of reactants and products involved. For example:
HSO+
2NaOH  NaSO+ 2HO
24 24 2sodium
hydroxide
sodium
sulfate
An ‘unbalanced’ equation can be balanced by multiplying
the different atoms and molecules on each side by different
amounts, so that they match.

Balancing equations
If you count the number of atoms of each type on each side
of this equation, you will see that they do not match.
H + 2SO4 NaOH Na2SO4 H2 + O
So, multiply the sodium atoms on the left by 2:
H + 2SO4 2NaOH Na2SO4 H2 + O
Now that the number of sodium atoms on each side is equal
the number of hydrogen atoms on the left side has increased.
So multiply the number of hydrogen atoms on the right by 2.
H + 2SO4 2NaOH Na2SO4 2H2 + O

Balancing equations for making salts

Indigestion remedies
The acid in your stomach that helps you break down your food
is called hydrochloric acid. It has a pH of between 1 and 2.
Indigestion and heartburn are caused
by an excess of acid in your stomach.
Indigestion remedies such
as Milk of Magnesia contain
antacids, like magnesium
oxide and calcium carbonate.
What do you think antacids do
to the acid in your stomach?

Metal oxide
Metal oxides are compounds made from a metal and oxygen.
For example, burning magnesium in oxygen produces
magnesium oxide.
magnesium + oxygen  magnesium oxide
Acids react with metal oxides to make a salt and water.
For example, sulfuric acid reacts with copper oxide to make
copper sulfate and water.
copper
oxide
copper
sulfate

Base or alkali?
Bases are substances that
react with acids, which include
metals oxides, hydroxides and
carbonates.
Alkalis are substances that
react with acids and which
are soluble in water.
bases: react
with acids
alkalis:
soluble in
water
Copper oxide is a base, but not an alkali, because it reacts
with acids, but does not dissolve in water.
Sodium hydroxide is an alkali (and a base), because it reacts
with acids and it is soluble in water.

Acids and metal oxides

Making copper sulfate

Metal oxides + acids

What is the formula?

Formulae
How do we know that the formula of sodium chloride is NaCl,
while the formula of copper chloride is CuCl2?
It is because of the combining power of the atoms.
 Sodium has a combining power of 1, so it bonds with one
other atom.
 Chlorine also has a combining power of 1, so it bonds
with one other atom.
 Copper, though, has a combining power of 2, so it needs
to bond to two chlorine atoms.
The formula of magnesium chloride is MgCl2, so what do you
think is the combining power of magnesium?

Formulae and combining powers
Here are the combining powers of some metal and non-metal
atoms:
combining
power
1
1
2
2
metal atom
Na
K
Mg
Cu
non-metal
atom
combining
power
Cl
F
O
N
1
1
2
3

Formulae and combining powers

Acid and carbonate
When a carbonate reacts
with an acid, it gives off
carbon dioxide gas.
How could you test the
gas given off, to confirm
that it is carbon dioxide?
What would you
observe in this test?
carbon dioxide
limewater

Acid and carbonate
The products of the reaction between a carbonate and an
acid are a salt, carbon dioxide and water.
Calcium carbonate is a substance
that is naturally found in the shells
of sea creatures and snails.
What salt do you think will be produced by the reaction of
hydrochloric acid and calcium carbonate?
calcium
carbonate
calcium
chloride
hydrochloric
acid
carbon
dioxide +
+  + water

Reaction of carbonates

Acid and metal
Acids also react with metals to make a gas.
When an acid reacts with a metal, the gas
produced makes a lighted splint go pop.
What is this gas?
A salt is also produced during the
reaction. What is the name of the salt
that will be produced by the reaction
of hydrochloric acid with calcium?
+ calcium
 + hydrogen
acid calcium
chloride
hydrochloric

Choose your reaction
Some metals react violently with acids, so it wouldn’t be safe
to use them to make a salt in the classroom.
However, if you still wanted to make that salt, you could use
the metal carbonate instead.
Sodium reacts very violently with sulfuric acid, so should not
be uses to make sodium sulfate. However, you could safely
use sodium carbonate.
sulfuric
acid +  carbon
sodium
carbonate
sodium
sulfate
dioxide + + water
Could you safely use sodium hydroxide to make sodium
sulfate? What about sodium oxide?

Choose your reaction

What is acid rain?
Rainwater has a pH of about 5.6, which
means that it is naturally slightly acidic.
This natural acidity is due to carbon
dioxide in the air dissolving into the rain,
forming a weak acid called carbonic acid.
Rainwater with a lower pH than normal
is called acid rain.
Burning of fossil fuels in power stations and cars forms
pollutants such as sulfur dioxide and nitrogen oxides.
These gases dissolve in rainwater to make sulfuric acid and
nitric acid, which are strong acids, so also form acid rain.
Why is acid rain a serious environmental problem?

How does acid rain work?

Effects of acid rain
Acid rain has many damaging effects on the environment:
 The acids in acid rain speed
up the chemical weathering
of rocks and buildings.
 Rivers, lakes and streams
become more acidic so
that animals and plants
cannot live in them.
 Soil that becomes more acidic has fewer nutrients so trees
and other plants cannot grow. Acid rain also damages
trees by breaking down the waxy coating of leaves.
What can be done to reduce acid rain and its effects?

Reducing acid rain
Governments are working to reduce the emissions of the
acidic pollutants produced by burning fossil fuels.
 Sulfur dioxide is formed when coal containing sulfur is
burned in power stations. This acidic pollutant can be
removed from the gases before they are released into
the atmosphere.
 Nitrogen oxides are formed
when petrol burns in a car’s
engine. Exhaust systems
can be fitted with a catalytic
converter which turns harmful
gases into harmless gases.
How do these changes help to reduce acid rain?

Acid rain – a global problem
Forests in Scandinavian countries such as Sweden have
suffered greatly from the damaging effects of acid rain.
However, scientists have shown that
the acid rain that falls in Sweden is
not produced there. The source of the
acidic pollutants is in fact more likely
to be UK factories and power stations.
This happens because air pollution
can be carried high up into the sky,
where it is pushed by strong winds
towards other countries.
Is it right that a country can directly cause pollution in another?

Should pollution be contained?

Limiting the effects of acid rain: opinions

Glossary

Anagrams

Multiple-choice quiz

Reactions of acids

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Reactions of acids