Transcript Structures and Bonding

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C3: Chemical Economics
OCR Gateway Additional Science
W Richards
The Weald School
Fundamental Concepts
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Elements
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If a solid, liquid or gas is made up of only one type of
atom we say it is an element. For example, consider a
tripod made up of iron:
These atoms are
ALL iron – there’s
nothing else in here
Compounds
Compounds are formed
when two or more
elements are
chemically combined.
Some examples:
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Methane
Sodium
chloride (salt)
Glucose
Chemical formulae
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The chemical formulae of a molecule or compound is simply a
way of showing the ratio of atoms in it. For example…
Na
Cl
= sodium chloride (NaCl)
K
I
= potassium iodide (KI)
O
K
N
O
O
= potassium nitrate (KNO3)
Some simple compounds…
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Methane, CH4
Water, H2O
Carbon
dioxide, CO2
Key
Hydrogen
Ethyne, C2H2
Oxygen
Sulphuric
acid, H2SO4
Carbon
Sulphur
Chemical formulae
Try drawing these:
1) Water H2O
2) Carbon dioxide CO2
3) Calcium sulphate CaSO4
4) Magnesium hydroxide Mg(OH)2
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Naming compounds
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Rule 1– If two identical elements combine then the
name doesn’t change
This happens with the following elements:
1) H2
4) F2
2) N2
5) Cl2
3) O2
6) Br2
These elements always go
around in pairs (diatomic
molecules). For example,
hydrogen looks like this:
Naming compounds
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Rule 2 – When two elements join and one is a halogen,
oxygen or sulphur the name ends with ____ide
e.g. Magnesium + oxygen
magnesium oxide
1) Sodium + chlorine
6) KBr
2) Magnesium + fluorine
7) LiCl
3) Lithium + iodine
8) CaO
4) Chlorine + copper
9) MgS
5) Oxygen + iron
10)KF
Naming compounds
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Rule 3 – When three or more elements combine and two of
them are hydrogen and oxygen the name ends with
hydroxide
e.g. Sodium + hydrogen + oxygen
Sodium hydroxide
1) Potassium + hydrogen + oxygen
2) Lithium + hydrogen + oxygen
3) Calcium + hydrogen + oxygen
4) Mg(OH)2
Naming compounds
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Rule 4 – When three or more elements combine and
one of them is oxygen the ending is _____ate
e.g. Copper + sulphur + oxygen
Copper sulphate
1) Calcium + carbon + oxygen
6) AgNO3
2) Potassium + carbon + oxygen
7) H2SO4
3) Calcium + sulphur + oxygen
8) K2CO3
4) Magnesium + chlorine + oxygen
5) Calcium + oxygen + nitrogen
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
Simple formulae to learn
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“Covalent” formulae
“Ionic” formulae
H2O
Water
NaCl
Sodium chloride
CO2
Carbon dioxide
CaCl2
Calcium chloride
NH3
Ammonia
MgO
Magnesium oxide
H2
Hydrogen
HCl
Hydrochloric acid
Sulphuric acid
O2
Oxygen
H2SO4
HNO3
Nitric acid
N2
Nitrogen
NaOH
Sodium hydroxide
SO2
Sulphur dioxide
Ca(OH)2
Calcium hydroxide
CaCO3
Calcium carbonate
Al2O3
Aluminium oxide
Fe2O3
Iron oxide
Bonding revision
Cl
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
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Bonding
Here comes my friend, Sophie
Sodium
Cl
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Na
Hey Johnny. I’m in Group 1 so I have
one electron in my outer shell. I’m quite
happy to get rid of it. Do you want it?
Okay
+
Cl
Na
Now we’ve both got full outer shells
and we’ve both gained a charge.
We’re both called IONS and we’ve
formed an IONIC bond.
Covalent 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
H
Now we’re both really stable. We’ve
formed a covalent bond, a bond that
often forms between non-metals.
C3a-c Rates of Reaction
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Rates of Reaction introduction
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Which of these reactions would be classed as “a fast rate of
reaction” and which would be slow?
Measuring the Rate of Reaction
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Two common methods:
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 – “limiting reactant”
Slower reaction
Time
Rate of reaction = amount of product formed/reactant used up
time
Common units are g/s, g/min, cm3/s or cm3/min
Rate of reaction graph
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Q. What if less reactants were used?
Amount of
product
formed/
reactant
used up
Time
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) The ______ the reactants are under
Words – activation, quicker, pressure, 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 - catalysts
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Amount of
product
formed/
reactant
used up
With catalyst
Without
catalyst
Time
An example question
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Consider the following graph showing the mass
lost during a reaction between marble chips of
different surface areas and acid:
1) How much mass had
been lost for the large
chips in the first
200s?
2) How much extra mass
had been lost by the
small chips (compared
to large) after 400s?
3) What mass of large
chips would you
predict to have left
after 500s?
0.8g
0.2g
94.2g
Dust Explosions
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The aftermath of an explosion
at the CTA Acoustics
manufacturing plant in
Kentucky – the factory had a
build up of resin dust in the
air
(source: US Chemical Safety Board)
An exploding custard truck
(source: Daily Telegraph)
C3d Reacting Masses
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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
Conservation of Mass
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Here’s a classic experiment where magnesium is burned in a crucible:
2Mg + O2
Mass of magnesium
and crucible before
burning = 78.25g
2MgO
Mass of magnesium and
crucible after burning =
78.56g
Mass is always conserved in any reaction,
so where did this extra mass come from?
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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 and21/07/2015
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
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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
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C3e Percentage Yield and Atom Economy
Problems with calculating masses
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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
Percentage Yield
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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
The theoretical yield is 136g (using Cl = 35.5) so the % yield is 75%
Percentage yield
Percentage yield =
Actual yield
Predicted yield
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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
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
61%
2) Making zinc chloride from zinc and hydrochloric acid:
Zn + 2HCl
ZnCl2 + H2
99%
Chemical Economics
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Hi. We’re industrial scientists and
we want to make lots of chemicals
and sell them to make money. What
problems would we face?
Possible problems with making
chemicals:
Therefore we need
reactions and
processes that give
us a high percentage
yield and high atom
economy.
1) Reactions often produce
chemicals that aren’t
commercially useful or that can’t
be sold
2) To reduce the costs we want to
make sure that no reactants are
wasted
C3f Energy
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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
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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
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Temp. after mixing/OC Exothermic or
endothermic?
Energy from fuels
Copper
calorimeter
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Water
Spirit burner
Fuel
Experimental values
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Step 1: Calculate the energy gained by the water:
Energy gained by water = mass of water x 4.18 J/gC0 x change
in temperature
Step 2: Divide this value by the mass of the alcohol used to
find out the energy gained by the water per gram of alcohol
Energy gained per gram = (answer to Step 1) / mass of alcohol
burned
An example calculation
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While doing this experiment, Dave got the following results for methanol:
Mass of
water
Start
temp
End temp
Temp diff
Start mass
End mass
Mass diff
100g
16
51
35
159.67
158.22
1.45
Step 1: 100g x 4.18 J/gC0 x 35 = 14630 J
Step 2: 14630 / 1.45 = 10090 J/g
Therefore energy given out by the alcohol =
10090J/g
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Other ways of finding an energy change
The amount of energy produced by a reaction can also be
found by measuring an energy change:
By mixing the reactants in an
insulated container the energy
change can be measured by
observing the change in
temperature.
C3g Batch or Continuous?
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Batch and Continuous processes
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In summary:
Process
Batch
Continuous
What it means
Reactants are thrown
in, the reaction
happens and the batch
is removed
The reactants are
continually fed in and the
products are continually
removed (e.g. the Haber
Process)
Advantages
Makes a wide variety
Operate all the time and
of products on demand automatically, makes a large
amount of product
Disadvantages
More labour intensive
Can only make one product
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Researching new drugs: An introduction
to
thalidomide
Mat Fraser,
comedian and actor
Tony Melendez,
guitarist
Developing new drugs
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Before a new drug can be approved it has to go through a
strict testing process. Consider the example of thalidomide:
Date
Event
Mid 1950s
Animal testing using thalidomide was undertaken.
Tests showed that it was safe but the tests were
“inadequate” – no tests were done on pregnant animals
Late 1950s
Thalidomide prescribed to pregnant mothers to help
sleep and morning sickness problems
Early 1960s
Babies are born with birth defects and the drug was
banned worldwide. Around 12,000 deformed
Thalidomide babies born, 4,000 die in first year.
Mid 1960s
Tests show that Thalidomide can help leprosy
sufferers and it is still used today for this purpose.
Developing new medicines
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An expensive process…:
Step 1 - research
Step 2 - development
Step 3 - legalities
Step 4 - manufacture
Step 5 - marketing
Extracting Raw Materials from Plants
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Step 1: Crush
the plant
Step 2: Remove oil
by pressing
OR step 3: Remove oil by
boiling and dissolving in a
suitable solvent
…or chromatography
can be used…
Chromatography
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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?
As well as using
chromatography, scientists
also use data relating to
melting points and boiling
points to analyse the
purity of a substance.
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Sudan 1
Dye 1
Dye 2
Dye 3
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C3h Allotropes of Carbon and Nanochemistry
Forms of Carbon
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Choose a form of carbon and research the following:
1) What properties does this form of carbon have?
2) How are the electrons arranged in this structure?
3) How does the structure of this form affect its properties?
Allotropes of Carbon
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1) Diamond – very hard, doesn’t conduct electricity,
very high melting point, insoluble in water. Each
carbon atom is bonded to four other carbon atoms.
2) Graphite – soft, does conduct electricity,
very high melting point, insoluble in water.
Each carbon atom is bonded to three others
causing graphite to have free electrons
3) Buckminsterfullerene – 60 carbon atoms
arranged in a sphere
Nanoscience
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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.
Two examples of nanotechnology
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The “Nano Carbon Pro” tennis racket uses
nanoparticles to increase its strength.
Nanotubes can be used in electrical
circuits, drug delivery systems and used
as catalysts due to their small size but
large surface area: