Download Unit C3 - Chemistry In Action

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EdExcel Triple Science Unit C3
Chemistry in Action
W Richards
The Weald School
Topic 1 – Quantitative Analysis
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Chemical Economics
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Hi. We’re industrial scientists and
we want to analyse this chemical.
What tests could we do?
There are two main types of analysis:
1) Qualitative – descriptions of what
is present
You need to use different
tests for different ions – for
example, if this chemical
contains copper chloride then
we’d need to verify by testing
for copper ions and testing
for chloride ions.
2) Quantitative – analysis of how
much of a chemical is present
Tests like these are important
for industries like the water
industry and medicine. Why?
Testing using Precipitates
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Some metal compounds form precipitates, i.e. an insoluble solid that is
formed when sodium hydroxide is added to them. Consider calcium
chloride:
CaCl2
+
2NaOH
Ca(OH)2 + 2NaCl
What precipitates are formed with the following metal compounds when
they react with sodium hydroxide?
Metal ion
Precipitate
formed
Calcium
Calcium hydroxide
Aluminium
Copper
Iron(II)
Iron(III)
Soluble or
insoluble?
Colour
White
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Ammonium, nitrate, bromide and iodide ions
Ammonium ions:
Add sodium hydroxide, warm it and test the gas using damp
litmus paper – ammonia gas turns damp litmus paper blue.
Chloride, bromide and iodide ions:
Add a few drops of dilute nitric acid followed by a few drops
of silver nitrate solution. A white precipitate should be
formed for chloride ions, a pale yellow precipitate should be
formed for bromide ions and a darker yellow precipitate for
iodide ions.
Flame tests revision
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Compounds containing lithium, sodium, potassium, calcium and
barium ions can be recognised by burning the compound and
observing the colours produced:
Lithium
Sodium
Potassium
Calcium
Barium
Red
Yellow
Lilac
Brick red
Green
Testing for carbonate ions
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Limewater
Limewater turns
milky/cloudy
Calcium carbonate + hydrochloric acid
calcium chloride + carbon dioxide + water
Topic 2 – Quantitative Analysis
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Water
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Amazing facts about water:
1) 95% of your body mass is water (94% in women due to a higher body
fat content)
2) Dinosaurs would have drunk the same water you do
3) Water dissolves more substances than any other liquid – most ionic
substances are soluble and most covalent substances are insoluble
4) Around 75% of the world’s surface is made of water
5) To feel thirsty you need to lose around 1% of your body water
6) 5,000 children die every day due to not having clean drinking water
7) An average person in the West uses 200-300 litres of water every day
Hard and Soft Water
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Definition: Hard water is water that contains lots
of dissolved ions like magnesium and calcium that
come from contact with rocks. When it reacts with
soap it forms scum.
Advantages of hard water
Disadvantages of hard water
Dissolved ions are good for
your health
More soap is needed to form
lather
They also help reduce the
development of heart
disease
Can lead to deposits forming
(e.g. limescale) so its more
expensive
There are two types of hard water – permanent and
temporary. What is the difference between these two?
Temporary hard water
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Temporary hard water is water that contains
hydrogencarbonate ions (HCO3-). You can boil this water to
soften it up and here’s what happens:
Step 1 – The hydrogencarbonate ions
decompose to produce carbonate ions
Step 2 – The carbonate ions react
with calcium and magnesium ions to
form precipitates
Measuring Water Hardness
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Hardness can be measured by adding soap and seeing how
much soap it takes to form a lather:
No. of drops of soap needed to form a lather
Water sample
Before boiling
After boiling
A
27
27
B
25
4
C
4
4
1) Which sample is soft water?
2) Which sample is temporary hard water?
3) Which sample is permanent hard water?
Removing hardness
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One way to remove permanent hardness:
Pass the water through an “ionexchange” column that
contains a special resin to
“swap” the calcium and
magnesium ions for sodium
or hydrogen ions. This is
how some commercial water
softeners work.
Resin
Ca2+
Resin
Na+
Resin
Na+
Ca2+
Na+
Ca2+
The Mole
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Definition: A mole is a measure of the number of
particles in a substance. 1 mole is 6x1023 particles.
Molar Mass (g/mol)
Molar mass is the mass of one mole of a substance and is equal
to the relative atomic mass (in grams).
For example:
1) Carbon has a relative atomic mass of 12, so 1mol of carbon
atoms would have a mass of 12g
2) Aluminium has a relative atomic mass of 27, so 1mol of
aluminium atoms would have a mass of ___g
3) Sodium hydroxide has a relative atomic mass of 40, so
2mols of NaOH would have a mass of ____g
Molar Calculations
Mass (g)
No. of moles =
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N= m
Molar mass (g/mol)
M
Some example questions:
1) Calculate the mass of 4mol of lithium
2) Calculate the mass of 2mol of sodium
3) Calculate the number of moles in 36g of carbon
4) Calculate the number of moles in 88g of carbon dioxide
5) Calculate the number of moles in 27g of water
A note about volume…
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The two most commonly used units of volume in chemistry are
the cm3 and the dm3:
1cm3
1dm3 (= 1000cm3)
1) Convert 1250cm3 into dm3
2) Convert 1cm3 into dm3
3) Convert 0.056dm3 into cm3
4) Convert 1.28dm3 into cm3
Concentration
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Concentration means “how much of a chemical there is in a
fixed volume” and can be measured in g/dm3 or mol/dm3.
A solution of low
concentration (“dilute”)
A solution of high
concentration (“strong”)
Questions on Concentration
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To calculate the concentration of a substance you could use
one of these formulae:
Conc. = Mass of substance (g)
Conc. = Amount of solute (mol)
Volume of solvent (dm3)
Volume of solvent (dm3)
Calculate, with units, the concentration of the following:
1) A solution of 10g salt in 1dm3 of water
2) 2mol of hydrochloric acid in 500cm3 of water
3) 10kg of salt in 200dm3 of water
4) 0.5mol of sodium hydroxide in 100cm3 of water
Converting concentrations
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To convert g/dm3 into mol/dm3 you can use the following
formula:
Concentration = Concentration (g/dm3)
(mol/dm3)
Molar mass
Convert the following:
1) 0.5mol/dm3 of sodium hydroxide into g/dm3.
2) 2mol/dm3 of HCl into g/dm3.
3) 20g/dm3 of NaCl into mol/dm3.
4) 500g/dm3 of CaCl2 into mol/dm3.
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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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
Common acids and alkalis
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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
Titration
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1) Fill a burette with sodium hydroxide
solution of known concentration
2) Accurately measure out 25cm3 of acid
and place it in the conical flask
3) Add phenolphthalein indicator to the
flask
4) Slowly add the alkali until the mixture in
the flask turns pink
5) Repeat until you get similar results
Using the correct indicator
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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
4
5
Strong acid
6
7
8
9
10
11
Neutral
12 13 14
Strong alkali
Because of the gradual colour changes it’s not a very good
indicator to use for titration. It’s better to use an indicator
with a sudden colour change:
Indicator
Colour in acid
Colour in alkali
Litmus
Red
Blue
Phenolphthalein
Colourless
Pink
Screened methyl orange
Purple
Green
Using the correct indicator
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Strong acid + strong alkali – use any indicator
Strong acid + weak alkali – use methyl orange indicator
Weak acid + weak alkali – use phenolphthalein indicator
Titration Equations
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Q. 0.05dm3 of HCl neutralises 0.1dm3 of NaOH of concentration
0.5mol dm-3. What is the concentration of the acid?
The key steps:
1) Look at the equation to compare the numbers of moles:
HCl + NaOH
NaCl + H2O
Notice that 1 mole of HCl neutralises 1 mole of NaOH
2) Use this equation:
No. of moles = concentration x volume
a) So, the number of moles of NaOH is (0.5 x 0.1) = 0.05mol
b) According to the equation, this will neutralise 0.05mol of HCl
c) Therefore we have (0.05mol/0.05dm3) = 1mol dm-3 HCl
Titration Equations
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1) 0.2dm3 of HCl neutralises 0.1dm3 of NaOH of concentration
0.5mol dm-3. What is the concentration of the acid?
HCl + NaOH
NaCl + H2O
2) H2SO4 of concentration 0.4mol dm-3 neutralises 0.1dm3 of
NaOH of concentration 0.2mol dm-3. How much acid was
used?
H2SO4 + 2NaOH
Na2SO4 + 2H2O
Topic 3 – Electrolytic Processes
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Electrolytes
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An electrolyte is an ionic substance that has been melted or
dissolved in water so that the ions are free to move:
Cl- Na+ ClNa+ Cl- Na+
Cl- Na+ ClNa+ Cl- Na+
Electrolysis
Positive
electrode
(“anode”)
Electrolyte
solution
containing
copper ions
(cations) and
chloride ions
(anions)
+
+
+
+
Cu2+
Cl-
Cl-
Cl-
Cu2+
Cu2+
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-
Negative
electrode
(“Cathode”)
Electrolysis
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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
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“Redox” reactions happen during electrolysis:
At the positive electrode (anode) the
negative ions LOSE electrons to
become neutral – this is
OXIDATION
At the negative electrode (cathode)
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
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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
Electrolysis of molten sodium chloride
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Sodium is a useful metal – it can be used in street lights and as
a coolant for nuclear reactors. It can be made from the
electrolysis of molten sodium chloride:
Positive
electrode
(“anode”)
+
+
+
+
Na+
Cl-
Cl-
Cl-
Na+
Na+
-
Negative
electrode
(“Cathode”)
Write half equations for these reactions and state where
oxidation and reduction occur
Electrolysis of Salt Water
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When solutions are electrolysed (instead of the molten compound) the
results are different. Consider the electrolysis of salty water (a
solution of sodium chloride):
Chlorine gas (Cl2)
Hydrogen gas (H2)
Sodium
chloride
solution (salt
water)
NaCl(aq)
Positive
electrode
Negative
electrode
Sodium hydroxide
(NaOH(aq))
Electrolysis of Solutions
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The electrolysis of sodium chloride solution brings different results to the
electrolysis of molten sodium chloride because of the presence of
hydrogen (H+) and hydroxide (OH-) ions. Two rules:
1) At the anode the “simplest” ion is discharged
– e.g., in the electrolysis of a chloride the Clion would be discharged (instead of the OHion) whereas in the electrolysis of a sulphate
the OH- ion would be discharged (instead of
the SO42- ion). The OH- ion will then form
oxygen at the anode.
2) At the cathode a metal will be discharged if
its less reactive then hydrogen. If it’s more
reactive than hydrogen then hydrogen will be
discharged.
+
+
+
+
-
Products from electrolysis
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Given these two rules, complete the following table:
Electrolyte
Copper chloride
solution
Copper sulfate
solution
Sodium sulfate
solution
Molten lead
bromide
Product at
cathode
Product at anode
Copper
Chlorine
Copper
Oxygen
Hydrogen
Oxygen
Lead
Bromine
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)
Electroplating
Silver
electrode
+
+
+
+
Solution containing
silver ions
Ag+
Ag+
Ag+
-
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Object to
be plated
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Topic 4 – Gases, Equilibria and Ammonia
Revision about Volume
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The two most commonly used units of volume in chemistry are
the cm3 and the dm3:
1cm3
1dm3 (= 1000cm3)
1) Convert 1250cm3 into dm3
2) Convert 1cm3 into dm3
3) Convert 0.056dm3 into cm3
4) Convert 1.28dm3 into cm3
Revision about 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
Calculating Volumes of Gases
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An important fact: 1 mole of a gas at room temperature
and pressure occupies a volume of 24dm3.
1) What is the volume of 2 moles of oxygen?
2) What is the volume of 0.25 moles of carbon dioxide?
3) How many moles would be in 8dm3 of nitrogen?
4) How much volume would 80g of argon occupy?
5) A balloon contains 12dm3 of carbon dioxide. What is the
mass of this much CO2?
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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
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Calculating the volume of a product
REMEMBER THIS - At normal temperature and pressure the
Relative Formula Mass (Mr) of a gas will occupy a volume of 24 litres
e.g. 2g of H2 has a volume of 24 litres
32g of O2 has a volume of 24 litres
44g of CO2 has a volume of 24 litres etc
Q. When water is electrolysed it breaks down into hydrogen and oxygen:
2H2O
2H2 + O2
What VOLUME of hydrogen is produced by the electrolysis of 6g of
water?
• On the previous page we said that the MASS of hydrogen produced
was 0.66g
•
2g of hydrogen (H2) will occupy 24 litres (from the red box above),
•
So 0.66g will occupy 0.66/2 x 24 = 8 litres
Example questions
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1) What volume of hydrogen is produced when 18g of water is
electrolysed?
2H2O
2H2 + O2
2) Marble chips are made of calcium carbonate (CaCO3). What
volume of carbon dioxide will be released when 500g of CaCO3 is
reacted with dilute hydrochloric acid?
CaCO3 + 2HCl
CaCl2 + H2O + CO2
3) Magnesium will react with hydrochloric acid. What volume of
hydrogen would be produced if you reacted 1g of magnesium with
excess acid?
Mg + 2HCl
MgCl2 + H2
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 “dynamic
equilibrium”):
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 came up with the Haber Process
that uses nitrogen from the air and hydrogen from natural
gas to make ammonia:
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
Eutrophication
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Ammonia is used to make fertilisers. One possible problem with fertilisers
is eutrophication. Eutrophication is when lakes become stagnant due to
careless use of fertiliser…
1) Inorganic fertilisers
used on fields are
washed into the lake
3) This growth causes
overcrowding and many plants die
due to lack of enough light or food
2) The fertiliser causes increased growth in water plants
Eutrophication
4) Microorganisms and
bacteria increase in number due
to the extra dead material
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6) The lack of oxygen
causes the death of fish
and other aquatic animals
Can’t…breathe…
5) These microorganisms
use up the oxygen in the
lake during respiration
Eutrophication
4) Microorganisms and
bacteria increase in number due
to the extra dead material
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6) The lack of oxygen
causes the death of fish
and other aquatic animals
5) These microorganisms
use up the oxygen in the
lake during respiration
Topic 5 – Organic Chemistry
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Ethanol
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Ethanol is a “clean burning” energy source and
produces little or no greenhouse gases. How is it
made?
Ford Escape E85 –
runs on 85% ethanol
Ethanol is produced from ethene, a chemical produced from the fractional
distillation of crude oil and involving cracking using a catalyst at high
temperature and pressure:
The “fossil fuel” way
Ethene + steam
ethanol
Ethene is produced by
“cracking” oil
...or by the fermentation of sugar from standard crops like sugar cane and
corn, under warm and anaerobic conditions:
The “renewable” way
Sugar
ethanol + carbon dioxide
This process uses yeast
as an enzyme
Making ethanol from ethene
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Ethene + water
C2H + H2O
ethanol
C2H5OH
Unused ethene recycled
Ethene
Reaction vessel with high
temperature and pressure
Ethanol
Distillation revision
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This apparatus can be used to
separate water and ethanol
because they have different
_____ ______. The ______
will evaporate first, turn back
into a _______ in the
condenser and collect in the
_______. The water remains
in the round flask, as long as
the _______ does not
exceed water’s boiling point.
This method can be used to
separate crude oil.
Words – temperature, boiling points, ethanol, beaker, liquid
Key facts about ethanol
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The following facts apply to ethanol:
1) They all dissolve in water to form a neutral solution
2) They are used as fuels and solvents and ethanol is the
main alcohol in alcoholic drinks
3) Ethanol can be dehydrated to form ethene
Remember us? When we’re making ethanol
there are two main things we need to
consider – how available are the raw
materials (sugar cane or crude oil) and how
good is the final product?
Alkanes
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Alkanes are SATURATED HYDROCARBONS. What does this
mean?
HYDROCARBONS are molecules that are made up of
hydrogen and carbon atoms
SATURATED means that all of these atoms are held
together by single COVALENT bonds, for example:
H
H
H
C
C
H
H
Ethane
H
H
H
H
H
H
C
C
C
C
H
H
H
H
H
Butane
Alkanes are fairly unreactive (but they do burn well). The
general formula for an alkane is CnH2n+2
General Formulae for Alkanes
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Alkanes form a homologous series (they have the same general
formula)… H
H
H
H
C
H
H
H
Methane (n=1)
H
H
H
H
C
C
C
H
H
H
Propane (n=3)
C
C
H
H
H
Ethane (n=2)
H
H
H
H
H
H
C
C
C
C
H
H
H
H
Butane (n=4)
General formula for alkanes = CnH2n+2
H
Alkenes
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Ethane
Ethene
Butane
Butene
ALKENES
ALKANES
Alkenes are different to alkanes; they contain DOUBLE
COVALENT bonds (a bond that has two shared electrons). For
example:
This double bond means that alkenes have the potential to join
with other molecules – this make them REACTIVE.
General Formulae for Alkenes
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Alkenes also form a homologous series…
H
H
H
C
C
H
H
H
H
H
C
C
C
H
H
Ethene (n=2)
H
Propene (n=3)
H
H
H
H
C
C
C
C
H
H
Butene (n=4)
H
Chemicals in the same homologous series
will have the same general formula, they
will show a gradual variation in one
property (e.g. increasing boiling points)
and have similar chemical properties.
General formula for alkenes = CnH2n
Alcohols
25/05/2017
Alcohols are a homologous series with a functional group –OH.
Some examples:
H
H
C
O
H
H
Methanol (n=1)
Methanol is an important raw
material used in the
manufacture of fuels, adhesives
and solvents.
H
H
H
C
C
H
H
O
H
Ethanol (n=2)
Ethanol can be oxidised using
agents or microbes to form
ethanoic acid, the main acid in
vinegar (a flavouring and
preservative).
General formula for alkanes = CnH2n+1OH
The next alcohol in this series is propanol. Write its formula
and draw its chemical structure.
Carboxylic acids
25/05/2017
Carboxylic acids form a homologous series with the functional
group –COOH. The presence of the –COOH gives carboxylic
acids their properties.
H
C
H
O
O
C
H
H
Methanoic acid
H
C
O
O
Ethanoic acid
H
H
H
H
C
C
H
H
C
1) They dissolve in water to form weak acidic solutions
2) They react with carbonates to form carbon dioxide
4) They react with bases
O
Propanoic acid
Some facts about carboxylic acids:
3) They react with metals
O
H
Esters
25/05/2017
Esters are compounds with the functional group –COO-. Ethyl ethanoate is
the main example and it is formed when ethanoic acid reacts with an
alcohol:
Ethanoic acid + ethanol
ethyl ethanoate + water
The reaction is carried out in the presence of a catalyst (e.g. concentrated
sulphuric acid). They have distinctive smells and are used perfumes and
food products.
Structural formula of this reaction:
H
H
C
H
C
O
O
Ethanoic acid
H
H
H
H
C
C
H
H
Ethanol
O
H
H
H O
H
H
C C O
C
C
H
H
H
H
Ethyl ethanoate
H
O
H
H
Water
Uses of Esters
25/05/2017
Perfumes are synthetically made from esters. Here are some
facts about perfumes. Why are these things important?
1) Perfumes are non-toxic
2) They are non-irritants
3) They evaporate easily
4) They do not dissolve in water
5) They don’t react with water
Polymers containing the ester functional group are also used to
make polyesters. Polyesters are fibres used to make clothing
or plastic bottles and they can be recycled to make fleece.
Healthy and Unhealthy Oils
25/05/2017
Unhealthy oils:
Healthy oils:
“Saturated”
“Unsaturated”
Oils and fats are both classed as esters.
Making Soap
25/05/2017
1) Take an oil and boil it with concentrated
alkali solution
2) The oils break down into glycerol and long
chain carboxylic acids
3) The acids then react with the alkali to
make a salt and water
4) So a lot of soaps are basically sodium or
potassium salts of long-chain carboxylic acids
How soap works
25/05/2017
Soaps work by having a “hydrophobic” and a
“hydrophilic” end. The hydrophobic end
dissolves in grease and the hydrophilic end
dissolves in water:
How they work:
A hydrophobic
soap anion
The soap anions surround the oil and form droplets around it,
which enables the grease to “lift out” of the stain.
Turning unsaturates into saturates
25/05/2017
600C, Nickel catalyst
The unsaturated fat is hardened by “catalytic
hydrogenation”. Hydrogenated oils have a higher
melting point and so are solid at room temperature,
making them useful for margarines and pastries.
As the filtered oil cools down it turns into a solid fat –
useful for margarine!