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AQA Chemistry 2
J McDougall
The structure of the atom
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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
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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
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How many protons, neutrons and electrons?
Isotopes
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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.
Electron structure
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Consider an atom of Potassium:
Potassium has 19 electrons.
These electrons occupy
specific energy levels
“shells”…
Nucleus
The inner shell has __ electrons
The next shell has __ electrons
The next shell has __ electrons
The next shell has the remaining __ electron
Electron structure
= 2,8,8,1
Periodic Table Introduction
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Periodic table
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The periodic table arranges all the elements
in groups according to their properties.
Vertical
columns are
called GROUPS
Mendeleev
Horizontal rows are called PERIODS
The Periodic Table
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Fact 1: Elements in the same group have the
same number of electrons in the outer shell (this
corresponds to their group number)
H
He
Li
Be
B
C
N
O
F
Ne
Na
Mg
Al
Si
P
S
Cl
Ar
K
Ca
Br
Kr
I
Xe
Fe
Ni
Cu
Zn
Ag
Pt
E.g. all group 1 metals
have __ electron in
their outer shell
Au
Hg
These elements have
__ electrons in their
outer shells
These elements
have __ electrons
in their outer shell
The Periodic Table
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Fact 2: As you move down through the periods an
extra electron shell is added:
Li
Be
Na
Mg
K
Ca
E.g. Lithium has 3
electron Hin the
configuration 2,1
He
Ni
Sodium hasFe11
electrons in the
configuration 2,8,1
Pt
Cu
Zn
Ag
Au
Potassium has 19 electrons in
the configuration __,__,__,__
Hg
B
C
N
O
F
Ne
Al
Si
P
S
Cl
Ar
Br
Kr
I
Xe
The Periodic Table
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Fact 3: Most of the elements are metals:
H
These elements
are metals
He
Li
Be
B
C
N
O
F
Ne
Na
Mg
Al
Si
P
S
Cl
Ar
K
Ca
Br
Kr
I
Xe
Fe
Ni
Cu
Zn
Ag
Pt
Au
This line divides
metals from nonmetals
Hg
These elements are
non-metals
The Periodic Table
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Fact 4: (Most important) All of the elements in
the same group have similar PROPERTIES. This
is how I thought of the periodic table in the first
place. This is called PERIODICITY.
H
He
Li
Be
B
C
N
O
F
Ne
Na
Mg
Al
Si
P
S
Cl
Ar
K
Ca
Br
Kr
I
Xe
Fe
Ni
Cu
Zn
Ag
Pt
Au 1Hgmetals. They all:
E.g. consider the group
1) Are soft
2) Can be easily cut with a knife
3) React with water
Compounds
Compounds are formed
when two or more
elements are
chemically combined.
Some examples:
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Methane
Sodium
chloride (salt)
Glucose
Some simple compounds…
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Methane, CH4
Water, H2O
Carbon
dioxide, CO2
Key
Hydrogen
Ethyne, C2H2
Oxygen
Sulphuric
acid, H2SO4
Carbon
Sulphur
Balancing equations
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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
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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
Ca
+
+
HCl
+ 2 O2
NaCl
CO2
+
+
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H2
H 2O
+ 2H2O
+ 2 H2O
Ca(OH)2
+
+
H2SO4
Na2SO4
+ 2H2O
2 CH3OH
+ 3 O2
2 NaOH
2 CO2
+ 4H2O
H2
Bonding
Cl
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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
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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
Now we’re both really stable.
We’ve formed a covalent bond.
H
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
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Na
Now we’ve both got full outer shells
and we’ve both gained a charge.
We’ve formed an IONIC bond.
Covalent bonding
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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
Dot and Cross Diagrams
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Water, H2O:
H
O
H
Dot and Cross Diagrams
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Oxygen, O2:
O
O
Dot and cross diagrams
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Water, H2O:
Step 1: Draw the atoms with
their outer shell:
H
Step 2: Put the atoms together and
check they all have a full outer shell:
O
H
O
H
H
Oxygen, O2:
O
O
O
O
Dot and cross diagrams
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Nitrogen, N2:
Methane CH4:
H
N
N
H
C
H
H
Ammonia NH3:
H
Carbon dioxide, CO2:
N
H
H
O
C
O
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Other ways of drawing covalent bonds
Consider ammonia (NH3):
H
N
H
H
H
N
H
H
H
N
H
H
Ions
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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
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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
As opposed to covalent bonds, ionic bonds form strong forces
of attraction between different ions due to their opposite
______, causing GIANT IONIC STRUCTURES to form (e.g
sodium chloride) with ______ melting and boiling points:
Some examples
Magnesium
chloride:
Mg
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2+
Cl
Cl
Mg
+
-
Cl
Cl
MgCl2
Calcium oxide:
Ca
+
2+
O
Ca
2-
O
CaO
Giant structures (“lattices”)
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1. Diamond – a giant
covalent structure with a
very ____ melting point
due to ______ bonds
between carbon atoms
3. Sodium chloride – a giant ionic lattice
with _____ melting and boiling points
due to ______ forces of attraction.
Can conduct electricity when _______.
2. Graphite – carbon atoms
arranged in a layered
structure, with free _______
in between each layer enabling
carbon to conduct _________
+
+
+
+
+
+
+
+
+
4. Metals – the
__________ in metals
are free to move around
(“delocalised”), holding
the _____ together
and enabling it to
conduct _________
A closer look at metals
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Metals are defined as elements that readily
lose electrons to form positive ions. There
are a number of ways of drawing them:
+
-
+
-
+
+
+
-
+
+
+
+
+
-
-
-
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
Delocalised electrons
Nanoscience
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Definition:
Nanoscience 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. They also have a large surface area to
volume ratio and their properties could lead to new
developments in computers, building materials etc.
Task: research nanoscience and find two current and/or
future applications of this science.
Group 1 – The alkali metals
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Li
Na
K
Rb
Cs
Fr
Group 1 – The alkali metals
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Some facts…
1) These metals all have ___
electron in their outer shell.
2) Density increases as you go down the
group, while melting point ________
2) Reactivity increases as you go _______ the group. This is because the
electrons are further away from the _______ every time a _____ is
added, so they are given up more easily.
3) They all react with water to form an alkali (hence their name) and
__________, e.g:
Potassium + water
2K(s)
+
2H2O(l)
potassium hydroxide + hydrogen
2KOH(aq)
+
H2(g)
Words – down, one, shell, hydrogen, nucleus, decreases
Group 0 – The Noble gases
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He
Ne
Ar
Kr
Xe
Rn
Group 0 – The Noble gases
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Some facts…
1) All of the noble gases have a full
outer shell, so they are very ______
2) They all have _____ melting and
boiling points
3) They exist as single atoms rather then _________ molecules
4) Helium is ________ then air and is used in balloons and
airships (as well as for talking in a silly voice)
5) Argon is used in light bulbs
(because it is so unreactive) and
argon , krypton and ____ are used
in fancy lights
Words – neon, stable, low, diatomic, lighter
Group 7 – The halogens
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F
Cl
Br
I
At
Group 7 – The Halogens
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1) Reactivity DECREASES
as you go down the group
Decreasing
reactivity
Some facts…
(This is because the electrons are further away from the
nucleus and so any extra electrons aren’t attracted as much).
2) They exist as
diatomic molecules (so
that they both have a
full outer shell):
Cl
Cl
3) Because of this fluorine and chlorine are liquid at room
temperature and bromine is a gas
The halogens – some reactions
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1) Halogen + metal:
+
+
Na
Cl
Halogen + metal
Cl
Na
ionic salt
2) Halogen + non-metal:
H
+
Cl
Halogen + non-metal
Cl
H
covalent molecule
Atomic mass
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RELATIVE ATOMIC MASS, Ar
(“Mass number”) = number of
protons + number of neutrons
SYMBOL
PROTON NUMBER = number of
protons (obviously)
Relative formula mass, Mr
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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”
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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...
Calculating percentage mass
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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
2) Potassium in potassium chloride, KCl
3) Calcium in calcium chloride, CaCl2
4) Oxygen in water, H2O
Recap questions
Work out the relative formula mass of:
1) Carbon dioxide CO2
2) Calcium oxide CaO
3) Methane CH4
Work out the percentage mass of:
1) Carbon in carbon dioxide CO2
2) Calcium in calcium oxide CaO
3) Hydrogen in methane CH4
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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 and25/05/2017
oxygen:
2H2O
2H2 + O2
What mass of hydrogen is produced by the electrolysis of 6g of water?
Work out Mr: 2H2O = 2 x ((2x1)+16) = 36
2H2 = 2x2 = 4
1.
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
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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
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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
Atom Economy
Percentage
atom economy =
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Relative formula mass of useful product
Total masses of products
Calculate the atom economies of the following:
1) Converting ethanol into ethene (ethene is the useful bit):
C2H5OH
C2H4 + H20
2) Making zinc chloride from zinc and hydrochloric acid:
Zn + 2HCl
ZnCl2 + H2
Numbers of moles
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Consider two liquids:
20cm3 of 0.1mol/dm3 of
hydrochloric acid
20cm3 of 0.1mol/dm3 of
sodium hydroxide
These two beakers contain the same number of moles
Now consider two gases:
20cm3 of helium at room
temperature and pressure
20cm3 of argon at room
temperature and pressure
These two gases contain the same number of moles
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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
Example reactions
Reaction
Sodium hydroxide + dilute
hydrochloric acid
Sodium
hydrogencarbonate +
citric acid
Copper sulphate +
magnesium powder
Sulphuric acid +
magnesium ribbon
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Temp. after mixing/OC Exothermic or
endothermic?
Reversible Reactions
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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
Reversible Reactions
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When a reversible reaction occurs in a CLOSED SYSTEM (i.e. no reactants
are added or taken away) an EQUILIBRIUM is achieved – in other words,
the reaction goes at the same rate in both directions:
A + B
Endothermic reactions
Increased temperature:
A + B
C + D
C + D
Exothermic reactions
Increased temperature:
A + B
C + D
More products
Less products
Decreased temperature:
Decreased temperature:
A + B
C + D
Less products
A + B
C + D
More products
Making Ammonia
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Guten Tag. My name is Fritz Haber and I won the Nobel
Prize for chemistry. I am going to tell you how to use a
reversible reaction to produce ammonia, a very important
chemical. This is called the Haber Process.
Nitrogen + hydrogen
Ammonia
N2 + 3H2
2NH3
Fritz Haber,
1868-1934
To produce ammonia from nitrogen and hydrogen you
have to use three conditions:
Nitrogen
Hydrogen
•High pressure
•450O C
•Iron catalyst
Mixture of NH3, H2 and
N2. This is cooled
causing NH3 to liquefy.
Recycled H2 and N2
Haber Process: The economics
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A while ago we looked at reversible reactions:
Endothermic, increased temperature
A + B
Endothermic
C + D
Exothermic, increase temperature
A + B
Nitrogen + hydrogen
Ammonia
N2 + 3H2
2NH3
C + D
Exothermic
1) If temperature was DECREASED the amount of ammonia formed would
__________...
2) However, if temperature was INCREASED the rate of reaction in both
directions would ________ causing the ammonia to form faster
3) If pressure was INCREASED the amount of ammonia formed would
INCREASE because there are less molecules on the right hand side of
the equation
Haber Process Summary
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A low temperature increases the yield of ammonia but is too
slow
A high temperature improves the rate of reaction but
decreases the yield too much
A high pressure increases the yield of ammonia but costs a lot
of money
To compromise all of these factors, these conditions are used:
Nitrogen
Hydrogen
•200 atm pressure
•450O C
•Iron catalyst
Mixture of NH3, H2
and N2. This is
cooled causing NH3
to liquefy.
Recycled H2 and N2
Rates of Reaction
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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
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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) Whether or not a _______ is used
Words – activation, quicker, catalyst, temperature, collide
Catalysts
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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
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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
Rate of reaction graph v1
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Time taken
for reaction
to complete
Reaction takes a
long time here
Reaction is
quicker
here
Temperature/
concentration
Rate of reaction graph v2
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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
Electrolysis
Positive
electrode
Solution
containing
copper and
chloride ions
+
+
+
+
Cu2+
Cl-
Cl-
Cl-
Cu2+
Cu2+
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-
Negative
electrode
Electrolysis
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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
Electrolysis equations
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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
Purifying Copper
Impure
copper
Solution
containing
copper ions
+
+ Cu
+ Cu
+ Cu
2+
2+
2+
At the positive electrode:
Cu(s)
Cu2+(aq) + 2e-
-
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Pure copper
At the negative electrode:
Cu2+(aq) + 2e-
Cu(s)
Electrolysis of brine
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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)
Hydrogen gas (H2)
Sodium
chloride (brine)
NaCl(aq)
Positive
electrode
Negative
electrode
Sodium hydroxide
(NaOH(aq))
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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
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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
Making salts
25/05/2017
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
25/05/2017
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.
Ammonium salts
25/05/2017
Guten tag again. When ammonia dissolves in
water it produces an alkaline solution:
NH3 + H20
NH4OH
This solution can be used to make fertilisers. Very
useful!
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