1. EdExcel Additional Science
22/09/2018
EdExcel Additional Science
Synthesis
W Richards
The Weald School

2. Sodium + water sodium hydroxide + hydrogen
Balancing equations
22/09/2018
Consider the following reaction:
Sodium + water sodium hydroxide + hydrogen Na O H O H Na + 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”)

3. Balancing equations We need to balance the equation:
22/09/2018
We need to balance the equation:
Sodium + water sodium hydroxide + hydrogen Na O H O H Na O H Na O H + H + Na
Now the equation is balanced, and we can write it as:
2Na(s) + 2H2O(l) NaOH(aq) + H2(g)

4. Some examples 2 2 3 2 3 Mg + O2 Zn + HCl Fe + Cl2 NaOH + HCl CH4 + O2
22/09/2018 2
Mg O2
Zn HCl
Fe Cl2
NaOH HCl
CH O2
Ca H2O
NaOH H2SO4
CH3OH O2
MgO
ZnCl H2
FeCl3
NaCl H2O
CO H2O
Ca(OH) H2
Na2SO H2O 2

5. Carbon Chemistry Introduction
22/09/2018
Carbon chemistry (“organic chemistry”) focuses on molecules made from carbon compounds: C

6. Alkanes Alkanes are SATURATED HYDROCARBONS. What does this mean?
22/09/2018
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 bonds, for example: C H
Ethane
Butane C H
Alkanes are fairly unreactive (but they do burn well).

7. General Formulae for Alkanes
22/09/2018
Instead of circles, let’s use letters…
Methane (n=1) H C
Ethane (n=2) H C
Propane (n=3) H C
Butane (n=4) H C
General formula for alkanes = CnH2n+2

8. Alkenes ALKANES ALKENES
22/09/2018
Alkenes are different to alkanes; they contain DOUBLE COVALENT bonds. For example:
Ethane
Ethene
ALKANES
ALKENES
Butane
Butene
The simple test for an alkene is to see if it will turn bromine water colourless.

9. General Formulae for Alkenes
22/09/2018
Ethene (n=2) H C
Propene (n=3) H C
Butene (n=4) H C
General formula for alkenes = CnH2n

10. Making ethanol from ethene
22/09/2018
Ethene + water ethanol
C2H + H C2H5OH
Ethene
Reaction vessel with high
temperature and pressure
Ethanol
Unused ethene recycled

11. For example, this bond can be “cracked” to give these:
Cracking
22/09/2018
Shorter chain hydrocarbons are in greater demand because they burn easier. They can be made from long chain hydrocarbons by “cracking”:
Butane
Ethane
For example, this bond can be “cracked” to give these:
Ethene

12. Cracking
22/09/2018
Gaseous hydrocarbon
Long chain hydrocarbon
Heated catalyst
Liquid hydrocarbon
This is a THERMAL DECOMPOSITION reaction, with clay used as a catalyst
Cracking can be used (as well as fractional distillation) to extract petrol from crude oil.

13. Monomers and Polymers
22/09/2018 C H
Ethene
Here’s ethene again. Ethene is called a MONOMER because it is just one small molecule. We can use ethene to make plastics…
Step 1: Break the double bond
Step 2: Add the molecules together:
This molecule is called POLYETHENE, and the process that made it is called POLYMERISATION

14. Another way of drawing it…
22/09/2018
Instead of circles, let’s use letters…
Ethene C H H C
Poly(e)thene
General formula for addition polymerisation: C n C n
e.g. C n H
CH3 C n H
CH3

15. Some examples
22/09/2018 C n H Cl Br C n H C n H Cl C n H Cl Br

16. Words – high, low, strong, weak, stretched, rigid
Structure of Plastics
22/09/2018
1) Some plastics have ____ intermolecular forces between each molecule – these have __ melting points and can be ________ easily. These are called thermoplastics
2) Some plastics have _____ forces between each molecule. These have ____ melting points and are ____. These are called thermosets.
Words – high, low, strong, weak, stretched, rigid

17. Changing properties of plastics
22/09/2018
Chemicals can be added to plastics to change their properties:
1) Plasticisers – these make the thermoplastics more ______. The plasticisers work by filling the gaps between molecule ______ allowing them to ____ over each other more easily.
UV and thermal stabilisers – these are added to increase the plastic’s _____
Crosslinking agents – these are added to the thermoplastics to encourage the molecules to form cross-links, which makes it more _____.
Words – stable, life, flexible, chains, slip

18. Words – recycling, greenhouse, decompose, biodegradable, poisonous
Disposal of plastics
22/09/2018
1) Landfill sites - most plastics do not _________ which means that landfill sites are quickly filled up. Research is being carried out on __________ plastics.
2) Burning – this releases carbon dioxide which causes the ________ effect, as well as other ________ gases.
3) _______ – the best option, but difficult because of the different types of plastic
Words – recycling, greenhouse, decompose, biodegradable, poisonous

19. 22/09/2018
Crude Oil

20. Hydrocarbons and crude oil
22/09/2018
Crude oil is a mixture of HYDROCARBONS (compounds made up of carbon and hydrogen). Some examples:
Increasing length C H
Ethane
Shorter chain hydrocarbons are in greater demand because they have more uses and release more energy during burning.
Butane C H

21. Healthy and Unhealthy Oils
22/09/2018
Unhealthy oils:
“Saturated”
Healthy oils (e.g. vegetable oil):
“Polyunsaturated”

22. Saturated vs. Unsaturated Fats
22/09/2018 C H
Ethene
Some oils are more healthy than others. Fish oils contain the nutrients Omega-3 and Omega-6. These oils are “unsaturated” like ethene:
Bromine water
Testing for double bonds:
Clearly, it is important for scientists to be able to test if a food contains “healthy” unsaturated fats or “unhealthy” saturated fats. Here’s how it’s done:
Bromine goes colourless
Oil (in ethanol)

23. Turning unsaturates into saturates
22/09/2018
The unsaturated fat is hardened by “hydrogenation”. Hydrogenated oils have a higher melting point and so are solid at room temperature and the food will last longer.

24. PROTON NUMBER = number of protons (obviously)
Atomic mass
22/09/2018
RELATIVE ATOMIC MASS, Ar (“Mass number”) = number of protons + number of neutrons He 2 4
SYMBOL
PROTON NUMBER = number of protons (obviously)

25. Relative formula mass, Mr
22/09/2018
The relative formula mass of a compound is the relative atomic masses of all the elements in the compound added together.
Relative atomic mass of O = 16
E.g. water H2O:
Relative atomic mass of H = 1
Therefore Mr for water = 16 + (2x1) = 18
Work out Mr for the following compounds:
HCl
NaOH
MgCl2
H2SO4
K2CO3
H=1, Cl=35 so Mr = 36
Na=23, O=16, H=1 so Mr = 40
Mg=24, Cl=35 so Mr = 24+(2x35) = 94
H=1, S=32, O=16 so Mr = (2x1)+32+(4x16) = 98
K=39, C=12, O=16 so Mr = (2x39)+12+(3x16) = 138

26. A classic exam question:
Empirical formulae
22/09/2018
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 = 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

27. Example questions
22/09/2018
Find the empirical formula of magnesium oxide which contains 48g of magnesium and 32g of oxygen.
Find the empirical formula of a compound that contains 42g of nitrogen and 9g of hydrogen.
Find the empirical formula of a compound containing 20g of calcium, 6g of carbon and 24g of oxygen.

28. Calculating the mass of a product
22/09/2018
E.g. what mass of magnesium oxide is produced when 60g of magnesium is burned in air?
IGNORE the oxygen in step 2 – the question doesn’t ask for it
Step 1: READ the equation:
2Mg + O MgO
Step 2: WORK OUT the relative formula masses (Mr):
2Mg = 2 x 24 = MgO = 2 x (24+16) = 80
Step 3: LEARN and APPLY the following 3 points:
48g of Mg makes 80g of MgO
1g of Mg makes 80/48 = 1.66g of MgO
60g of Mg makes 1.66 x 60 = 100g of MgO

29. Mr: 2Al2O3 = 2x((2x27)+(3x16)) = 204 4Al = 4x27 = 108
When water is electrolysed it breaks down into hydrogen and oxygen:
2H2O H2 + O2
What mass of hydrogen is produced by the electrolysis of 6g of water?
22/09/2018
Work out Mr: 2H2O = 2 x ((2x1)+16) = H2 = 2x2 = 4
36g of water produces 4g of hydrogen
So 1g of water produces 4/36 = 0.11g of hydrogen
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 + O CaO
Mr: 2Ca = 2x40 = CaO = 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?
2Al2O Al + 3O2
Mr: 2Al2O3 = 2x((2x27)+(3x16)) = Al = 4x27 = 108
204g produces 108g so 100g produces (108/204) x 100 = 52.9g of Al2O3

30. So mass of product = (4/36) x 6g = 0.66g of hydrogen
Another method
22/09/2018
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 H2 + O2
What mass of hydrogen is produced by the electrolysis of 6g of water?
Mass of product IN GRAMMES 4 6g 36
So mass of product = (4/36) x 6g = 0.66g of hydrogen

31. Total masses of products
Atom Economy
22/09/2018
Percentage atom economy =
Relative formula mass of useful product
Total masses of products
Calculate the atom economies of the following:
Converting ethanol into ethene (ethene is the useful bit):
C2H5OH C2H4 + H20
Making zinc chloride from zinc and hydrochloric acid:
Zn + 2HCl ZnCl2 + H2

32. Percentage Yield
22/09/2018
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

33. Percentage yield Percentage yield = Actual yield Predicted yield
22/09/2018
Percentage yield =
Actual yield
Predicted yield
X 100%
Some example questions:
The predicted yield of an experiment to make salt was 10g. If 7g was made what is the percentage yield?
Dave is trying to make water. If he predicts to make 15g but only makes 2g what is the percentage yield?
Sarah performs an experiment and has a percentage yield of 30%. If she made 50g what was she predicted to make?