12.6 – How can we use ions in
solutions?
11/01/2017
• Ionic compounds have many uses and can provide
other substances.
• Electrolysis is used to produce alkalis and
elements such as chlorine and hydrogen.
• Oxidation-reduction reactions do not just involve
oxygen.
• Soluble salts can be made from acids and
insoluble salts can be made solutions of ions.
Metal ions
Metal compounds in a solution contain metal ions. For example,
consider calcium chloride:
Calcium is in
group 2 and has
two electrons in
its outer shell, so
it will form a Ca2+
ion.
Chlorine is in
group 7 so a
chloride ion
will be Cl-
Calcium chloride has the formula CaCl2
Sodium atom
Chlorine atom
Electron transfer
Click Again
Sodium Chloride
+
-
Positive and negative ions attract
Electrolysis
11/01/2017
If you melt or dissolve an ionic compound (such as
NaCl or CuCl2), then the ions become free to move
around – and carry electrical current.
Molecule of solid
copper chloride
CuCl2 (s)
Molecule of solid
copper chloride after
being dissolved
chloride
ion
Copper
ion
CuCl2 (aq)
Electrolysis
11/01/2017
Electrolysis is used to separate a metal from its compound.
When we electrolysed
copper chloride the _____
chloride ions moved to the
______ electrode and the
______ copper ions moved
to the ______ electrode –
OPPOSITES ATTRACT!!!
= chloride ion
= copper ion
Purifying Copper
Impure
copper
Solution
containing
copper ions
+
+ Cu
+ Cu
+ Cu
At the anode:
Cu(s)
Cu2+(aq) + 2e-
2+
---
11/01/2017
Pure copper
2+
2+
At the cathode:
Cu2+(aq) + 2e-
Cu(s)
Electrolysis equations
11/01/2017
We need to be able to write “half equations” to show what
happens during electrolysis (e.g. for copper chloride):
At the negative electrode the
positive ions GAIN electrons to
become neutral copper ATOMS. The
half equation is:
Cu2+ + 2 e-
Cu
At the positive electrode the
negative ions LOSE electrons to
become neutral chlorine
MOLECULES. The half equation is:
2 Cl- - 2e-
Cl2
Oxidation and Reduction in Electrolysis
11/01/2017
At the positive
electrode the
negative ions LOSE
electrons –This is
called Oxidation.
The half equation is:
At the negative
electrode the
positive ions GAIN
electrons – this is
called Reduction.
The half equation is:
2Cl- - 2e-
Cu2+ + 2e-
Cl2
Cu
Oxidation Is Loss, Reduction Is Gain
(of electrons)
O I L R I G
Electrolysis of brine
11/01/2017
Sodium chloride (salt) is made of an alkali metal and a
halogen. When it’s dissolved we call the solution
“brine”, and we can electrolyse it to produce 3
things…
Chlorine gas (Cl2) – used to
kill bacteria and to make
acids, bleach and plastics
Hydrogen gas (H2) – used
to manufacture ammonia
and margarine
Sodium
chloride (brine)
NaCl(aq)
Positive
electrode
Negative
electrode
Sodium hydroxide
(NaOH(aq)). Used to
make soap, paper and
ceramics
Electrolysis - summary
11/01/2017
1. When an ionic substance is melted or dissolved in
water, the _____ are free to _______ about in the
solution.
2. Passing an ________ __________through these
_________ or dissolved ionic substances, breaks them
down into __________. This is called ___________.
3. During electrolysis, ___________ charged ions move
towards the negative electrode and ___________
charged ions move towards the positive ___________.
Move
molten
elements
electrode
ions
positively
negatively
electric current
electrolysis
Making Soluble Salts
11/01/2017
There are 3 types of reaction that can be used to make
soluble salts. All 3 involve:
• An Acid
• A metal or metal compound
Method 1
METAL + ACID
e.g. magnesium + hydrochloric acid
SALT + HYDROGEN
magnesium chloride + hydrogen
Method 2
METAL OXIDE + ACID
SALT +
WATER
Method 3
METAL HYDROXIDE (Alkali) + ACID
SALT
+ WATER
Making salts
To form the name of a salt, you just combine the name of the
metal involved, with the salt type associated with the acid.
Hydrochloric acid makes chlorides, Sulfuric makes sulfates, Nitric makes nitrates.
Complete the table as practice
Hydrochloric
acid
Sodium
hydroxide
Potassium
oxide
Calcium
Sulphuric acid
Nitric acid
Sodium chloride +
water
Potassium sulfate +
water
Calcium nitrate +
water
Reactions of metals with acids
When a metal reacts with an acid it gives off hydrogen
(which can be “popped” using a lit splint). The other
product is a salt.
METAL + ACID
e.g. magnesium + hydrochloric acid
SALT + HYDROGEN
magnesium chloride + hydrogen
Copy and complete the following reactions:
1) Calcium + hydrochloric acid
2) Zinc + hydrochloric acid
3) Iron + hydrochloric acid
4) Lithium + sulphuric acid
Quiz on acids and alkalis
Acid, alkali or both???
1) This a pH of less than 7
2) This could kill cells
3) A metal hydroxide (e.g. sodium hydroxide) would be an _____
4) When this reacts with a metal hydrogen is released
5) A metal carbonate (e.g. calcium carbonate) would be an _____
6) This would feel soapy on your skin
7) This could be a corrosive
8) This will turn universal indicator purple
9) This would taste sour
10) This means “a base that can be dissolved”
Neutralisation reactions
When acids and alkalis react together they will NEUTRALISE
each other. Neutralisation is an example of a displacement
reaction:
Sodium hydroxide
Na
Hydrochloric acid
H
OH
The sodium DISPLACES
the hydrogen from HCl
Na
Cl
Sodium chloride
H2O
Water
Cl
+
+
H ions and OH ions
11/01/2017
• H ions make acids acidic.
• OH ions make alkalis alkaline.
• The pH scale measures the alkalinity
or acidity of a solution.
+
During neutralisation reactions the H ions
react with the OH ions to form H2O
(water). H+ (aq) + OH-(aq) → H2O(l)
Neutralisation experiment
Sodium hydroxide + hydrochloric acid  sodium chloride + water
A ____ was formed during the reaction, and we could have separated
this by __________ the solution, allowing the salt to Crystallise. The
salt that we formed depended on the acid:
•Hydrochloric acid will make a CHLORIDE
•Nitric acid will make a _________
•Sulphuric acid will make a _________
Words to use – nitrate, neutralised, alkali, sulphate, salt, evaporating
Reactions of metal oxides with acid
11/01/2017
A metal oxide is a compound containing a metal and oxide. They are
sometimes called BASES. A BASE is simply an insoluble alkali – it
neutralises acids, but does not dissolve in water. For example:
Mg
O
O
Na
Magnesium oxide
Na
O
Al
Sodium oxide
METAL OXIDE
+
H
Mg
Al
ACID
O
Aluminium oxide
SALT
+
WATER
Cl
O
H
O
Cl
Cl
Copy and complete the following reactions:
1)
Magnesium oxide + hydrochloric acid
2)
Calcium oxide + hydrochloric acid
3)
Sodium oxide + sulphuric acid
Mg
Cl
H
O H
Using Bases to Make Salts
Because Bases are insoluble the procedure for making a salt
is very slightly different…
…Instead of simply evaporating off the water, you have to
first remove any remaining (or excess) Base by filtration.
1) Drop the base
into the acid…
2) Filter it to remove
any leftover base
3) Evaporate it
to get the salt
Ammonium Salts
11/01/2017
• Ammonia (NH3) is a gas that dissolves in water to make
an alkali (Ammonium hydroxide).
• This can then be used to make Ammonium salts by
reacting it with an acid.
Ammonia
+
Nitric acid
Ammonium Nitrate
NH3(g)
+
HNO3(aq)
NH4NO3(aq)
• Notice how NO water is made in this neutralisation
reaction.
• Ammonium salts make good fertilisers because plants
need nitrogen to make proteins (to grow). Ammonium
Nitrate is the best for this purpose – can you see
why??
Making Insoluble Salts
11/01/2017
• Doesn’t usually require an acid.
• Insoluble salts can be made by mixing appropriate
solutions of ions (soluble salts), so that a precipitate is
Barium chloride + Sodium sulfate
Barium sulfate + Sodium chloride
formed.
BaCl2(aq)
+
Na2SO4(aq)
BaSO4(s)
Precipitation can be used to remove
unwanted ions from solutions, for example
in treating water for drinking or in treating
effluent. – The filter is covered in ions,
which form precipitates with ions in the
water.
+
2NaCl(aq)
An example question on reactivity
Which metal is most reactive?
Metal
A
B
C
D
E
Reaction with
dilute acid
Reaction with
water
Reaction with
oxygen
Some reaction
Slow reaction
Burns brightly
No reaction
No reaction
Reacts slowly
No reaction
No reaction
No reaction
Violent reaction
Slow reaction
Burns brightly
Reasonable
reaction
Reacts with
steam only
Reacts slowly