12/03/2014
Chemistry Unit 2
AQA
C2.1 Structures and Bonding
12/03/2014
Compounds
Compounds are formed
when two or more
elements are
chemically combined.
Some examples:
12/03/2014
Methane
Sodium
chloride (salt)
Glucose
Some simple compounds…
12/03/2014
Methane, CH4
Water, H2O
Carbon
dioxide, CO2
Key
Hydrogen
Ethyne, C2H2
Oxygen
Sulphuric
acid, H2SO4
Carbon
Sulphur
Balancing equations
12/03/2014
Consider the following reaction:
Sodium + water
Na
+
sodium hydroxide + hydrogen
Na
O
H
H
O
H
+
H
H
This equation doesn’t balance – there are 2 hydrogen
atoms on the left hand side (the “reactants” and 3 on
the right hand side (the “products”)
Balancing equations
12/03/2014
We need to balance the equation:
Sodium + water
sodium hydroxide + hydrogen
Na
O
H
Na
+
Na
H
O
O
H
Na
H
O
H
+
H
H
Now the equation is balanced, and we can write it as:
2Na(s) + 2H2O(l)
2NaOH(aq) + H2(g)
H
Some examples
2Mg
O2
2 MgO
Zn
+ 2 HCl
ZnCl2
2 Fe
+ 3Cl2
2 FeCl3
NaOH
CH4
+
+
HCl
+ 2 O2
NaCl
CO2
+
+
12/03/2014
H2
H2O
+ 2H2O
+ 2 H2O
Ca(OH)2
+
+
H2SO4
Na2SO4
+ 2H2O
2 CH3OH
+ 3 O2
Ca
2 NaOH
2 CO2
+ 4H2O
H2
Electron structure revision
12/03/2014
Draw the electronic structure of the following atoms:
Nucleus
Nucleus
Nucleus
Electron structure
Electron structure
Electron structure
= 2,5
= 2,8,2
= 2,8,8,2
Bonding
Cl
12/03/2014
Hi. My name’s Johnny Chlorine.
I’m in Group 7, so I have 7
electrons in my outer shell
I’d quite like to have a full outer
shell. To do this I need to GAIN
an electron. Who can help me?
Cl
Bonding
Cl
12/03/2014
Here comes one of my friends, Harry
Hydrogen
Hey Johnny. I’ve only got one
electron but it’s really close to my
nucleus so I don’t want to lose it.
Fancy sharing?
Cl
H
H
Now we’re both really stable as we
both have a full outer shell, like
the noble gases do. We’ve formed
a covalent bond.
Bonding
Here comes another friend, Sophie
Sodium
Cl
Na
Hey Johnny. I’m in Group 1 so I have
one electron in my outer shell. Unlike
Harry, this electron is far away from
the nucleus so I’m quite happy to get
rid of it. Do you want it?
Okay
+
Cl
12/03/2014
Na
Now we’ve both got full outer shells
and we’ve both gained a charge.
We’ve formed an IONIC bond.
Ions
12/03/2014
An ion is formed when an atom gains or loses electrons and
becomes charged:
+
-
The electron is negatively charged
The proton is positively charged
If we “take away” the electron
we’re left with just a positive
charge:
+
+
This is called an ion (in this case, a positive hydrogen ion)
Ionic bonding
12/03/2014
This is where a metal bonds with a non-metal (usually). Instead of sharing
the electrons one of the atoms “_____” one or more electrons to the
other. For example, consider sodium and chlorine:
Na
Sodium has 1 electron on its outer shell
and chlorine has 7, so if sodium gives
its electron to chlorine they both have
a ___ outer shell and are ______.
-
+
A _______
charged
sodium ion
Na
Cl
Cl
A _________
charged
chloride ion
Group 1 _______ will always form ions with a charge of +1 when they react
with group 7 _______. The group 7 element will always form a negative
ion with charge -1.
Words – full, transfers, positively, negatively, metals, halogens, stable
Some examples of ionic bonds -
12/03/2014
Magnesium
chloride:
Mg
2+
Cl
Cl
Mg
+
-
Cl
Cl
MgCl2
Calcium oxide:
Ca
+
2+
O
Ca
2-
O
CaO
Covalent bonding
12/03/2014
Consider an atom of hydrogen:
Notice that hydrogen has just __ electron in its outer
shell. A full (inner) shell would have __ electrons, so two
hydrogen atoms get together and “_____” their electrons:
Now they both have a ____ outer shell and are
more _____. The formula for this molecule is H2.
When two or more atoms bond by sharing electrons we
call it ____________ BONDING. This type of bonding
normally occurs between _______ atoms. It causes the
atoms in a molecule to be held together very strongly
but there are ____ forces between individual molecules.
This is why covalently-bonded molecules have low melting
and boiling points (i.e. they are usually ____ or ______).
Words – gas, covalent, non-metal, 1, 2, liquid, share, full, weak, stable
12/03/2014
Other ways of drawing covalent bonds
Consider ammonia (NH3):
H
N
H
H
H
N
H
H
H
N
H
Bonds formed between non-metals are usually covalent.
Common examples are NH3, CO2, CH4, H2O etc.
H
A closer look at metals
Metals are defined as elements that readily
lose electrons to form positive ions. The
electrons in the highest shells are delocalised
and able to move around, causing the ions to
be held together by electrostatic forces.
There are a number of ways of drawing this:
+
-
+
-
+
+
+
-
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+ + + + +
+
+
-
-
+
+
+
+
12/03/2014
+
Delocalised electrons
C2.2 Structures and Properties
12/03/2014
Properties of simple molecules
12/03/2014
Recall our model of a simple covalent compound like hydrogen,
H2:
H
H
1) The intermolecular
forces are very weak so each
one of these H2 molecules
doesn’t really care about the
others – it’s very easy to pull
them apart.
Hydrogen has a very
low melting point and a
very low boiling point.
Why?
2) When a substance is
heated it is the intermolecular
forces that are overcome,
NOT the covalent bond in
each molecule, which is much
stronger!
Also, the molecules do not carry a charge so covalent
compounds usually do not conduct electricity.
Giant Ionic Structures
When many positive and negative ions
are joined they form a “giant ionic
lattice” where each ion is held to the
other by strong electrostatic forces
of attraction. This is an “ionic bond”:
12/03/2014
Cl- Na+ Cl- Na+ Cl- Na+
Na+ Cl- Na+ Cl- Na+ ClCl- Na+ Cl- Na+ Cl- Na+
Na+ Cl- Na+ Cl- Na+ Cl-
If these ions are strongly held together what affect would
this have on the substance’s:
1) Melting point?
2) Boiling point?
3) State (solid, liquid or gas) at room temperature?
Dissolving Ionic Structures
12/03/2014
When an ionic structure like sodium chloride is dissolved it
enables the water to conduct electricity as charge is carried
by the ions:
Cl- Na+ ClNa+ Cl- Na+
Cl- Na+ ClNa+ Cl- Na+
12/03/2014
Giant Covalent structures (“lattices”)
1. Diamond – a giant
covalent structure with a
very ____ melting point
due to ______ bonds
between carbon atoms
2. Graphite – carbon atoms arranged in a
layered structure, with free _______
in between each layer enabling carbon to
conduct _________ (like metals)
O
Si
O
O
O
O
O
Si
Si
O
O
O
O
3. Silicon dioxide (sand) – a giant covalent
structure of silicon and oxygen atoms with
strong _____ causing a high ______ point
and it’s a good insulator as it has no free
electrons
Words – melting, high, electrons, bonds, strong, electricity
Using Covalent Structures
12/03/2014
Element/
compound
Property
Uses
Why?
Carbon –
diamond
Very hard
Drill tips
Silicon
dioxide
High melting
point
(1610OC)
Furnace
linings
Extremely
strong
covalent
structure
Very difficult
to melt
Silica glass
Doesn’t
conduct
electricity
Electrical
insulators
No free
electrons to
carry charge
Fullerenes
12/03/2014
Carbon can also be used to make structures called
“fullerenes”. Fullerenes are compounds used for applications
such as drug delivery, lubricants, catalysts and nanotubes and
they have structures based on carbon atoms forming
hexagonal rings:
Understanding Resistance
12/03/2014
As we’ve said before, metals have delocalised electrons that
enable them to conduct electricity and heat very well:
Electrons
Ions
Notice that the ions were vibrating and getting in the way of
the electrons – this is “resistance”. The easier the electrons
get through, the better the metal is at conducting electricity
and heat.
Metals and Alloys
12/03/2014
Metals are also easy to bend. This is because the layers slide
over each other:
A pure metal:
An alloy is a mixture
of metals that
causes the metal to
behave differently:
Smart Alloys
12/03/2014
A “smart alloy” is one that can “remember” its original state
after being bent or stretched.
These glasses are made from a “smart” material like nitinol – if
they are bent they will return to their original shape
Polymers
12/03/2014
Depending on the materials used and the conditions under
which they are made, polymers will have different properties.
Consider the example of poly(e)thene:
High Density Polythene
(HDPE)
Low Density Polythene
(LDPE)
- Stronger
- Weaker
- Stiffer
- More flexible
- Higher crystallinity
- Less crystallinity
Structure of Polymers
12/03/2014
“Thermosoftening”:
1) Some plastics have ____
intermolecular forces
between each molecule –
these have __ melting points
and can be ________ easily.
“Thermosetting”:
2) These plastics have _____
forces between each
molecule. These have ____
melting points and are ____.
Words – high, low, strong, weak, stretched, rigid
Nanotechnology
12/03/2014
Task: To find out what nanotechnology is and what it is used
for
1) What is nanotechnology?
2) Define the terms nanoparticle and nanocomposite
3) Gives some examples of its uses
4) Describe some of the future uses of this technology
5) Describe some of the ethical concerns over this technology
Nanotechnology
12/03/2014
Definition:
Nanotechnology is a new branch of science that refers to
structures built from a few hundred atoms and are 1100nm big. They show different properties to the same
materials in bulk, partly because they also have a large
surface area to volume ratio and their properties could
lead to new developments in computers, building materials
etc.
Two examples of nanotechnology
12/03/2014
The “Nano Carbon Pro” tennis racket uses
nanoparticles to increase its strength.
Silver nanoparticles can be used to give
fibres antibacterial properties – look at
what they do to e-coli bacteria:
Normal
e-coli
E-coli affected
by silver
nanoparticles
C2.3 Quantitative Chemistry
12/03/2014
Atomic Structure Revision
12/03/2014
The Ancient Greeks used to believe that
everything was made up of very small particles. I
did some experiments in 1808 that proved this
and called these particles ATOMS:
Dalton
NEUTRON –
neutral, same
mass as
proton (“1”)
PROTON –
positive, same
mass as
neutron (“1”)
ELECTRON –
negative, mass
nearly nothing
Mass and atomic number
12/03/2014
Particle
Relative Mass
Relative Charge
Proton
1
+1
Neutron
1
0
Electron
Very small
-1
MASS NUMBER = number of
protons + number of neutrons
SYMBOL
PROTON NUMBER = number of
protons (obviously)
Mass and atomic number
12/03/2014
How many protons, neutrons and electrons?
Isotopes
12/03/2014
12/03/2014
An isotope is an atom with a different number of neutrons:
Notice that the mass number is different. How many
neutrons does each isotope have?
Each isotope has 8 protons – if it didn’t then it just
wouldn’t be oxygen any more.
Atomic mass
12/03/2014
RELATIVE ATOMIC MASS, Ar
(“Mass number”) = number of
protons + number of neutrons
SYMBOL
PROTON NUMBER = number of
protons (obviously)
Relative formula mass, Mr
12/03/2014
The relative formula mass of a compound is the relative atomic
masses of all the elements in the compound added together.
E.g. water H2O:
Relative atomic mass of O = 16
Relative atomic mass of H = 1
Therefore Mr for water = 16 + (2x1) = 18
Work out Mr for the following compounds:
1) HCl
H=1, Cl=35 so Mr = 36
2) NaOH
Na=23, O=16, H=1 so Mr = 40
3) MgCl2
Mg=24, Cl=35 so Mr = 24+(2x35) = 94
4) H2SO4
H=1, S=32, O=16 so Mr = (2x1)+32+(4x16) = 98
5) K2CO3
K=39, C=12, O=16 so Mr = (2x39)+12+(3x16) = 138
A “Mole”
12/03/2014
Definition:
A mole of a substance is the relative formula
mass of that substance in grams
For example, 12g of carbon would be 1 mole of carbon...
...and 44g of carbon dioxide (CO2) would be 1 mole etc...
Types of Analysis
12/03/2014
The two types of analysis:
Qualitative – a method used to describe the
chemicals in a substance (e.g. using indicator paper
to see if something is an acid or alkali).
Quantitative – any method used to determine the
amount of chemicals, e.g. calculating the
concentration of acid in a substance through
titration.
Instrumental methods can be used in some types of analysis.
Instrumental methods are accurate, sensitive and rapid and
particularly useful for small samples.
Chromatography
12/03/2014
Chromatography is a technique used to find out what unknown
mixtures are made of. Substances are separated by the
movement of a “mobile phase” through a “stationary phase”.
In paper chromatography, the _____ is the
stationary phase and the ______ is the mobile
phase.
R
G
B
Different _____ spread out and stop at different
points due to their different ____ and properties.
They can then be identified by comparing to
standard reference materials. For each
component, a _______ equilibrium is set up
between the stationary and mobile phases.
Words – chemicals, paper, dynamic, solvent, sizes
Chromatography
12/03/2014
Chromatography can be used to separate a mixture of
different inks. Some example questions…
R
G
B
X
1) Ink X contains two
different colours. What
are they?
1
2
3
2) Which ink is ink Z
made out of?
Z
Gas Chromatography
12/03/2014
Gas chromatography works by separating a
mixture and then timing how long it takes a
substance to travel through the machine.
Different molecules travel at different speeds.
Abundance
of different
molecules
A mass
spectrometer is
used to find the
masses of these
molecules and
identify them
How many molecules
are here and which
ones are the most
abundant?
Molecule
Chromatography
Chromatography can
be used to test which
foods contain which
ingredients. For
example, consider the
dye Sudan 1, which was
found in 450 foods in
2005. Which dye
contains Sudan 1?
12/03/2014
Sudan 1
Dye 1
Dye 2
Dye 3
Calculating percentage mass
12/03/2014
If you can work out Mr then this bit is easy…
Percentage mass (%) =
Mass of element Ar
Relative formula mass Mr
x100%
Calculate the percentage mass of magnesium in magnesium oxide, MgO:
Ar for magnesium = 24
Ar for oxygen = 16
Mr for magnesium oxide = 24 + 16 = 40
Therefore percentage mass = 24/40 x 100% = 60%
Calculate the percentage mass of the following:
1) Hydrogen in hydrochloric acid, HCl
3%
2) Potassium in potassium chloride, KCl
52%
3) Calcium in calcium chloride, CaCl2
36%
4) Oxygen in water, H2O
89%
Empirical formulae
12/03/2014
Empirical formulae is simply a way of showing how many atoms are in a
molecule (like a chemical formula). For example, CaO, CaCO3, H20 and
KMnO4 are all empirical formulae. Here’s how to work them out:
A classic exam question:
Find the simplest formula of 2.24g of iron
reacting with 0.96g of oxygen.
Step 1: Divide both masses by the relative atomic mass:
For iron 2.24/56 = 0.04
For oxygen 0.96/16 = 0.06
Step 2: Write this as a ratio and simplify:
0.04:0.06 is equivalent to 2:3
Step 3: Write the formula:
2 iron atoms for 3 oxygen atoms means the formula is Fe2O3
Example questions
12/03/2014
1) Find the empirical formula of magnesium oxide which
contains 48g of magnesium and 32g of oxygen.
MgO
2) Find the empirical formula of a compound that contains
42g of nitrogen and 9g of hydrogen.
NH3
3) Find the empirical formula of a compound containing 20g
of calcium, 6g of carbon and 24g of oxygen.
CaCO3
12/03/2014
Calculating the mass of a product
E.g. what mass of magnesium oxide is produced when 60g of
magnesium is burned in air?
Step 1: READ the equation:
2Mg + O2
2MgO
IGNORE the
oxygen in step 2 –
the question
doesn’t ask for it
Step 2: WORK OUT the relative formula masses (Mr):
2Mg = 2 x 24 = 48
2MgO = 2 x (24+16) = 80
Step 3: LEARN and APPLY the following 3 points:
1) 48g of Mg makes 80g of MgO
2) 1g of Mg makes 80/48 = 1.66g of MgO
3) 60g of Mg makes 1.66 x 60 = 100g of MgO
1) When water is electrolysed it breaks down into hydrogen and12/03/2014
oxygen:
2H2O
2H2 + O2
What mass of hydrogen is produced by the electrolysis of 6g of water?
Work out Mr:
1.
2H2O = 2 x ((2x1)+16) = 36
2H2 = 2x2 = 4
36g of water produces 4g of hydrogen
2. So 1g of water produces 4/36 = 0.11g of hydrogen
3. 6g of water will produce (4/36) x 6 = 0.66g of hydrogen
2) What mass of calcium oxide is produced when 10g of calcium burns?
2Ca + O2
Mr: 2Ca = 2x40 = 80
2CaO
2CaO = 2 x (40+16) = 112
80g produces 112g so 10g produces (112/80) x 10 = 14g of CaO
3) What mass of aluminium is produced from 100g of aluminium oxide?
2Al2O3
4Al + 3O2
Mr: 2Al2O3 = 2x((2x27)+(3x16)) = 204
4Al = 4x27 = 108
204g produces 108g so 100g produces (108/204) x 100 = 52.9g of Al2O3
Another method
12/03/2014
Try using this equation:
Mass of product IN GRAMMES
Mass of reactant IN GRAMMES
Mr of product
Mr of reactant
Q. When water is electrolysed it breaks down into hydrogen and oxygen:
2H2O
2H2 + O2
What mass of hydrogen is produced by the electrolysis of 6g of water?
Mass of product IN GRAMMES
6g
4
36
So mass of product = (4/36) x 6g = 0.66g of hydrogen
Problems with this technique
12/03/2014
Calculating the amount of a product may not always give you a
reliable answer...
1) The reaction may not have completely _______
2) The reaction may have been _______
3) Some of the product may have been ____
4) Some of the reactants may have produced other _______
The amount of product that is made is called the “____”.
This number can be compared to the maximum theoretical
amount as a percentage, called the “percentage yield”.
Words – lost, yield, finished, reversible, products
Percentage Yield
12/03/2014
Theoretical yield = the amount of product that should be made
as calculated from the masses of atoms
Actual yield = what was actually produced in a reaction
Percentage yield
=
actual yield (in g)
theoretical yield
Example question:
65g of zinc reacts with 73g of hydrochloric acid and
produces 102g of zinc chloride. What is the percentage
yield?
Zn + 2HCl
ZnCl2 + H2
Percentage yield
Percentage yield =
Actual yield
Predicted yield
12/03/2014
X 100%
Some example questions:
1) The predicted yield of an experiment to make salt was
10g. If 7g was made what is the percentage yield?
70%
2) Dave is trying to make water. If he predicts to make 15g
but only makes 2g what is the percentage yield?
13%
3) Sarah performs an experiment and has a percentage yield
of 33%. If she made 50g what was she predicted to
make?
150g
Reversible Reactions
12/03/2014
Some chemical reactions are reversible. In other words, they
can go in either direction:
A + B
e.g. Ammonium chloride
NH4Cl
C + D
Ammonia + hydrogen chloride
NH3 + HCl
C2.4 Rates of Reaction
12/03/2014
Rates of Reaction
12/03/2014
Oh no! Here comes
another one and it’s
got more energy…
Here comes another
one. Look at how slow
it’s going…
It missed!
Here comes an acid particle…
No effect! It didn’t
have enough energy!
Hi. I’m Mike Marble. I’m
about to have some acid
poured onto me. Let’s see
what happens…
Rates of Reaction
12/03/2014
Chemical reactions occur when different
atoms or molecules _____ with enough
energy (the “________ Energy):
Basically, the more collisions we get the _______ the
reaction goes. The rate at which the reaction happens
depends on four things:
1) The _______ of the reactants,
2) Their concentration
3) Their surface area
4) The ______ the reactants are under
Words – activation, quicker, pressure, temperature, collide
Catalysts
12/03/2014
Task
Research and find out about two uses of catalysts in industry,
including:
1) Why they are used
2) The disadvantages of each catalyst
Catalyst Summary
12/03/2014
Catalysts are used to ____ __ a reaction to increase the rate
at which a product is made or to make a process ________.
They are not normally ___ __ in a reaction and they are
reaction-specific (i.e. different reactions need _________
catalysts).
Words – different, speed up, used up, cheaper
Measuring the Rate of Reaction
12/03/2014
Two common methods:
Rate of reaction graph v1
12/03/2014
Time taken
for reaction
to complete
Reaction takes a
long time here
Reaction is
quicker
here
Temperature/
concentration
Rate of reaction graph v2
12/03/2014
Amount of
product
formed/
amount of
reactant used
up
Fast rate
of reaction
here
Slower rate of reaction here
due to reactants being used up
Slower reaction
Time
Rate of reaction = amount of product formed/reactant used up
time
12/03/2014
C2.5 Endothermic and Exothermic Reactions
12/03/2014
Endothermic and exothermic reactions
Step 1: Energy must
be SUPPLIED to
break bonds:
Step 2: Energy is
RELEASED when new
bonds are made:
Energy
Energy
A reaction is EXOTHERMIC if more energy is RELEASED
then SUPPLIED. If more energy is SUPPLIED then is
RELEASED then the reaction is ENDOTHERMIC
12/03/2014
Common examples of these reactions
Are these reactions exothermic or
endothermic?
Burning
Photosynthesis
Cooling packs
Hand warmer packs
Example reactions
Reaction
Sodium hydroxide + dilute
hydrochloric acid
Sodium
hydrogencarbonate +
citric acid
Copper sulphate +
magnesium powder
Sulphuric acid +
magnesium ribbon
12/03/2014
Temp. after mixing/OC Exothermic or
endothermic?
Reversible Reactions recap
12/03/2014
Some chemical reactions are reversible. In other words, they
can go in either direction:
A + B
e.g. Ammonium chloride
NH4Cl
C + D
Ammonia + hydrogen chloride
NH3 + HCl
If a reaction is EXOTHERMIC in one direction
what must it be in the opposite direction?
For example, consider copper sulphate:
Hydrated copper
sulphate (blue)
+ Heat
CuSO4.5H2O
Anhydrous copper
sulphate (white)
CuSO4 + H2O
+
Water
C2.6 Acids and Alkalis
12/03/2014
12/03/2014
Universal Indicator and the pH scale
Universal Indicator is a mixture of liquids that will produce a
range of colours to show how strong the acid or alkali is:
1
2
3
Stomach acid
4
5
Lemon juice
6
7
8
9
10
11
12 13 14
Water Soap Baking powder Oven cleaner
Strong alkali
Strong acid
Neutral
An acid contains hydrogen ions, H+
An alkali contains hydroxide ions, OH-
Neutralisation reactions
12/03/2014
When acids and alkalis react together they will NEUTRALISE
each other:
Sodium hydroxide
Na
Hydrochloric acid
H
OH
The sodium “replaces”
the hydrogen from HCl
Na
Cl
Sodium chloride
General equation:
H2O
Water
H+(aq) + OH-(aq)
H2O(l)
Cl
Common acids and alkalis
12/03/2014
Acids
Alkalis
Hydrochloric acid, HCl
Sodium hydroxide, NaOH
Nitric acid, HNO3
Potassium hydroxide, KOH
Sulphuric acid, H2SO4
Magnesium hydroxide, Mg(OH)2
Calcium hydroxide, Ca(OH)2
Making salts
12/03/2014
Whenever an acid and alkali neutralise each other we are left
with a salt, like a chloride or a sulphate. Complete the
following table:
Hydrochloric
acid
Sodium
hydroxide
Potassium
hydroxide
Calcium
hydroxide
Sulphuric acid
Nitric acid
Sodium chloride +
water
Potassium
sulphate + water
Calcium nitrate +
water
Making Salts
12/03/2014
Soluble salts can be made from acids by reacting them with:
1) Metals, e.g.
Zn + 2HCl
ZnCl2 + H2
2) Insoluble bases, e.g.
CuO + 2HCl
CuCl2 + H20
3) Alkalis (alkali = a “soluble base”), e.g.
NaOH + HCl
NaCl + H20
Salts can be made from these solutions by crystallizing them.
Metal ions and precipitates
12/03/2014
Some metal ions form precipitates, i.e. an insoluble solid that
is formed when sodium hydroxide is added to them. Consider
calcium chloride:
Ca2+(aq)
+ 2OH-
Ca(OH)2 (s)
Precipitation can be used to remove unwanted ions, for
example, from drinking water.
Metal ion
Calcium Ca2+
Aluminium Al3+
Magnesium Mg2+
Copper(II) Cu2+
Precipitate formed
Calcium hydroxide: Ca2+(aq) + OH-(aq)
Colour
Ca(OH)2 (s)
White
Ammonium salts
12/03/2014
Guten tag. When ammonia dissolves in water
it produces an alkaline solution:
NH3 + H20
Fritz Haber,
1868-1934
NH4OH
This solution can be used to make
fertilisers. Very useful! I won the Nobel
Prize for Chemistry for my work in making
ammonia
C2.7 Electrolysis
12/03/2014
Dissolving Ionic Structures
12/03/2014
Remember that when an ionic structure like sodium chloride is
dissolved it enables the water to conduct electricity as charge
is carried by the ions:
Cl- Na+ ClNa+ Cl- Na+
Cl- Na+ ClNa+ Cl- Na+
Electrolysis
Positive
electrode
Solution
containing
copper and
chloride ions
+
+
+
+
Cu2+
Cl-
Cl-
Cu2+
12/03/2014
-
Negative
electrode
In anyCuelectrolysis
process the
2+
Clproducts
formed depend on the
reactivity of the different elements
Electrolysis
12/03/2014
During electrolysis the substance being broken down is called
the “electrolyte”.
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
Redox reactions
12/03/2014
“Redox” reactions happen during electrolysis:
At the positive electrode the
negative ions LOSE electrons to
become neutral – this is
OXIDATION
At the negative electrode the
positive ions GAIN electrons to
become neutral – this is
REDUCTION
These two processes are
called REDOX REACTIONS
OILRIG –
Oxidation Is Loss of electrons
Reduction Is Gain of electrons
Electrolysis half equations
12/03/2014
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- - 2 e-
Cl2
Electroplating
Silver
electrode
+
+
+
+
Solution containing
silver ions
Ag+
Ag+
Ag+
-
12/03/2014
Object to
be plated
Electrolysis of Salt Water
12/03/2014
Salt water (e.g. seawater or brine) can be electrolysed to
produce chlorine and other useful products:
Chlorine gas (Cl2) – useful
for making bleach and
plastics
Hydrogen gas (H2)
Sodium
chloride
solution (salt
water)
NaCl(aq)
Positive
electrode
Negative
electrode
Sodium hydroxide
(NaOH(aq)) – useful
for making soaps
Extracting Aluminium
12/03/2014
Aluminium has to be extracted from its ore (called ________) by
electrolysis. This is because aluminium is very ___________. The ore
is mixed with cryolite to lower its ________ ________. The ore is
then melted so that the ions can ______. The positively charged
aluminium ions gather at the ___________ electrode. Oxygen forms
at the positive electrode and causes it to wear away, which means that
they have to be __________ frequently.
Words – melting point, replaced, negative, bauxite, reactive, move