# Topic: Crude oil to plastics (D)

## 1:32 know what is meant by the terms empirical formula and molecular formula

The empirical formula shows the simplest whole-number ratio between atoms/ions in a compound.

The molecular formula shows the actual number of atoms of each type of element in a molecule.

For example, for ethane:

Molecular formula = C2H6

Empirical formula = CH3

Here are some more examples:

NameMolecular formulaEmpirical Formula
penteneC5H10CH2
buteneC4H8CH2
glucoseC6H12O6CH2O
hydrogen peroxideH2O2HO
propaneC3H8C3H8

Notice from the table that several different molecules can have the same empirical formula, which means that it is not possible to deduce the molecular formula from the empirical formula without some additional information. Also notice that sometimes it is not possible to simplify a molecular formula into simpler whole-number ratio, in which case the empirical formula is equal to the molecular formula.

## 1:33 calculate empirical and molecular formulae from experimental data

Calculating the Empirical Formula Example: What is the empirical formula of magnesium chloride if 0.96 g of magnesium combines with 2.84 g of chlorine?

Step 1: Put the symbols for each element involved at the top of the page.

Step 2: Underneath, write down the masses of each element combining.

Step 3: Divide by their relative atomic mass (Ar).

Step 4: Divide all the numbers by the smallest of these numbers to give a whole number ratio.

Step 5: Use this to give the empirical formula.

(If your ratio is 1:1.5 then multiple each number by 2

If your ratio is 1:1.33 then x3. If your ratio is 1:1.25 x4)

Calculating the Molecular Formula

If you know the empirical formula and the relative formula mass you can work out the molecular formula of a compound. Example: A compound has the empirical formula CH2, and its relative formula mass is 56. Calculate the molecular formula.

Step 1: Calculate the relative mass of the empirical formula.

Step 2: Find out the number of times the relative mass of the empirical formula goes into the Mr of the compound.

Step 3: This tells how many times bigger the molecule formula is compared to the empirical formula.

Empirical formula calculations involving water of crystallisation

When you heat a salt that contains water of crystallisation, the water is driven off leaving the anhydrous (without water) salt behind. For example, barium chloride crystals contain water of crystallisation, and therefore would have the formula  BaCl2.nH2O  where the symbol ‘n’ indicates the number of molecules of water of crystallisation. This value can be calculated using the following method.

Example: If you heated hydrated barium chloride (BaCl2.nH2O) in a crucible you might end up with the following results. Step 1: Calculate the mass of the anhydrous barium chloride (BaCl2) and the water (H2O) driven off. Step 2: Use the empirical formula method to find the value of n in the formula. ## 1:46 understand how to use dot-and-cross diagrams to represent covalent bonds in: diatomic molecules, including hydrogen, oxygen, nitrogen, halogens and hydrogen halides, inorganic molecules including water, ammonia and carbon dioxide, organic molecules containing up to two carbon atoms, including methane, ethane, ethene and those containing halogen atoms ## 3:01 know that chemical reactions in which heat energy is given out are described as exothermic, and those in which heat energy is taken in are described as endothermic

Exothermic: chemical reaction in which heat energy is given out.

Endothermic: chemical reaction in which heat energy is taken in.

(So, in an exothermic reaction the heat exits from the chemicals so temperature rises)

## 3:02 describe simple calorimetry experiments for reactions such as combustion, displacement, dissolving and neutralisation

Calorimetry allows for the measurement of the amount of energy transferred in a chemical reaction to be calculated.

EXPERIMENT1: Displacement, dissolving and neutralisation reactions Example: magnesium displacing copper from copper(II) sulfate Method:

1. 50 cm3 of copper(II) sulfate is measured and transferred into a polystyrene cup.
2. The initial temperature of the copper sulfate solution is measured and recorded.
3. Magnesium is added and the maximum temperature is measured and recorded.
4. The temperature rise is then calculated. For example:
Initial temp. of solution (oC)Maximium temp. of solution (oC)Temperature rise (oC)
24.256.732.5 Note:  mass of 50 cm3 of solution is 50 g

The cup used is polystyrene because:

polystyrene is an insulator which reduces heats loss

EXPERIMENT2: Combustion reactions To measure the amount of energy produced when a fuel is burnt, the fuel is burnt and the flame is used to heat up some water in a copper container

Example: ethanol is burnt in a small spirit burner Method:

1. The initial mass of the ethanol and spirit burner is measured and recorded.
2. 100cm3 of water is transferred into a copper container and the initial temperature is measured and recorded.
3. The burner is placed under of copper container and then lit.
4. The water is stirred constantly with the thermometer until the temperature rises by, say, 30 oC
5. The flame is extinguished and the maximum temperature of the water is measured and recorded.
6. The burner and the remaining ethanol is reweighed. For example:
Mass of water (g)Initial temp of water (oC)Maximum temp of water (oC)Temperature rise (oC)Initial mass of spirit burner + ethanol (g)Final mass of spirit burner + ethanol (g)Mass of ethanol burnt (g)
10024.254.230.034.4633.680.78 The amount of energy produced per gram of ethanol burnt can also be calculated: ## 3:03 calculate the heat energy change from a measured temperature change using the expression Q = mcΔT

Calorimetry allows for the measurement of the amount of energy transferred in a chemical reaction to be calculated.

EXPERIMENT1: Displacement, dissolving and neutralisation reactions Example: magnesium displacing copper from copper(II) sulfate Method:

1. 50 cm3 of copper(II) sulfate is measured and transferred into a polystyrene cup.
2. The initial temperature of the copper sulfate solution is measured and recorded.
3. Magnesium is added and the maximum temperature is measured and recorded.
4. The temperature rise is then calculated. For example:
Initial temp. of solution (oC)Maximium temp. of solution (oC)Temperature rise (oC)
24.256.732.5 Note:  mass of 50 cm3 of solution is 50 g

EXPERIMENT2: Combustion reactions To measure the amount of energy produced when a fuel is burnt, the fuel is burnt and the flame is used to heat up some water in a copper container

Example: ethanol is burnt in a small spirit burner Method:

1. The initial mass of the ethanol and spirit burner is measured and recorded.
2. 100cm3 of water is transferred into a copper container and the initial temperature is measured and recorded.
3. The burner is placed under of copper container and then lit.
4. The water is stirred constantly with the thermometer until the temperature rises by, say, 30 oC
5. The flame is extinguished and the maximum temperature of the water is measured and recorded.
6. The burner and the remaining ethanol is reweighed. For example:
Mass of water (g)Initial temp of water (oC)Maximum temp of water (oC)Temperature rise (oC)Initial mass of spirit burner + ethanol (g)Final mass of spirit burner + ethanol (g)Mass of ethanol burnt (g)
10024.254.230.034.4633.680.78 The amount of energy produced per gram of ethanol burnt can also be calculated: ## 3:08 practical: investigate temperature changes accompanying some of the following types of change: salts dissolving in water, neutralisation reactions, displacement reactions and combustion reactions

Calorimetry allows for the measurement of the amount of energy transferred in a chemical reaction to be calculated.

EXPERIMENT1: Displacement, dissolving and neutralisation reactions Example: magnesium displacing copper from copper(II) sulfate Method:

1. 50 cm3 of copper(II) sulfate is measured and transferred into a polystyrene cup.
2. The initial temperature of the copper sulfate solution is measured and recorded.
3. Magnesium is added and the maximum temperature is measured and recorded.
4. The temperature rise is then calculated. For example:
Initial temp. of solution (oC)Maximium temp. of solution (oC)Temperature rise (oC)
24.256.732.5 Note:  mass of 50 cm3 of solution is 50 g

EXPERIMENT2: Combustion reactions To measure the amount of energy produced when a fuel is burnt, the fuel is burnt and the flame is used to heat up some water in a copper container

Example: ethanol is burnt in a small spirit burner Method:

1. The initial mass of the ethanol and spirit burner is measured and recorded.
2. 100cm3 of water is transferred into a copper container and the initial temperature is measured and recorded.
3. The burner is placed under of copper container and then lit.
4. The water is stirred constantly with the thermometer until the temperature rises by, say, 30 oC
5. The flame is extinguished and the maximum temperature of the water is measured and recorded.
6. The burner and the remaining ethanol is reweighed. For example:
Mass of water (g)Initial temp of water (oC)Maximum temp of water (oC)Temperature rise (oC)Initial mass of spirit burner + ethanol (g)Final mass of spirit burner + ethanol (g)Mass of ethanol burnt (g)
10024.254.230.034.4633.680.78 The amount of energy produced per gram of ethanol burnt can also be calculated: ## 4:02 understand how to represent organic molecules using empirical formulae, molecular formulae, general formulae, structural formulae and displayed formulae

The molecular formula shows the actual number of atoms of each element in a molecule.

The empirical formula shows the simplest whole number ratio of atoms present in a compound. So the molecular formula is a multiple of the empirical formula.

The general formula shows the relationship between the number of atoms of one element to another within a molecule. Members of a homologous series share the same general formula. The general formula for alkanes is CnH2n+2 and the general formula for alkenes is CnH2n.

A structural formula shows how the atoms in a molecule are joined together.

The displayed formula is a full structural formula which shows all the bonds in a molecule as individual lines.

The terms above are demonstrated with the example of butane. • Displayed formula:
• Molecular formula: C₄H₁₀
• Empirical formula: C₂H₅
• General formula (alkanes): CnH2n+2
• Structural formula: CH₃ – CH₂ – CH₂ – CH₃

The terms above are demonstrated with the example of ethene, which contains a double bond. • Displayed formula:
• Molecular formula: C₂H₄
• Empirical formula: CH₂
• General formula (alkenes): CnH2n
• Structural formula: CH₂ = CH₂

## 4:03 know what is meant by the terms homologous series, functional group and isomerism

A functional group is an atom or a group of atoms that determine the chemical properties of a compound.

For example the functional group of an alcohol is the -OH group and that of alkenes is the C=C carbon to carbon double bond.

A Homologous series is a group of substances with:

• the same general formula
• similar chemical properties because they have the same functional group
• a trend (graduation) in physical properties

Isomers are molecules with the same molecular formula but with a different structure.

## 4:04 understand how to name compounds relevant to this specification using the rules of International Union of Pure and Applied Chemistry (IUPAC) nomenclature. Students will be expected to name compounds containing up to six carbon atoms

The names of organic molecules are based on the number of carbon atoms in the longest chain. This chain is the longest consecutive line of carbon atoms, even if this line bends.

The name is based on the number of carbon atoms in the longest chain
1 Meth-
2 Eth-
3 Prop-
4 But-
5 Pent-
6 Hex-
7 Hept-
8 Oct-
9 Non-
10 Dec-

Hydrocarbons are molecules which contain only hydrogen and carbon.

Naming straight-chain alkanes

The simplest hydrocarbons are alkanes. They contain only single bonds, and have “-ane” in the name.

For example, the displayed formula of ethane (C₂H₆) is: The name “ethane” contains “eth-” because there are 2 carbon atoms in the longest chain, and the name contains “-ane” because the molecule only has single bonds so is an alkane.

Another example is pentane (C₅H₁₂) which has the displayed formula: The name “pentane” contains “pent-” because there are 5 carbon atoms in the longest chain, and the name contains “-ane” because the molecule only has single bonds, so is an alkane.

Remember, it does not matter if the longest consecutive line of carbons bends around. For example the displayed formula below still shows a very normal molecule of pentane (5 carbons in a row). Pentane is not normally drawn with the longest chain of carbons bent around because it could be confusing. You might also see the bonds drawn at angles. Don’t worry, the displayed formula below is still pentane, as can be seen by the fact there are 5 carbon atoms in the longest chain, surrounded by hydrogen atoms bonded to the carbon atoms by single bonds. A shorter way to express the detailed structure of an organic molecule is the structural formula. The structural formula for pentane is CH₃-CH₂-CH₂-CH₂-CH₃, which tells us the same information about the molecule as does the displayed formula, without the hassle of having to draw all the bonds or all the hydrogen atoms.

Naming straight-chain alkenes

Another simple group of hydrocarbons is the alkenes. They contain a carbon-to-carbon double bond, which also means they have two fewer hydrogen atoms than their corresponding alkane. An alkene has “-ene” in its name.

For example, the displayed formula for ethene (C₂H₄) is: and the displayed formula of propene (C₃H₆) is: With longer alkene molecules the double bond might appear in different locations of the carbon chain, so the name needs to be a little bit more complicated to be able to describe these differences clearly. A number is added in the middle of the name to indicate at which carbon the double bond starts.

So the displayed formula of pent-1-ene is: and this is the displayed formula of pent-2-ene: However, take care that when counting which carbon has the double bond. The numbers start from the end that produces the smallest numbers in the name. For example, this is the displayed formula for pent-1-ene again, but just drawn the other way round. It is still pent-1-ene (you can’t get pent-4-ene): Naming straight-chain alcohols

We get the same pattern all over again with the group of organic molecules called alcohols, which are recognised by an -OH functional group. For example here is the displayed formula for ethanol, which has 2 carbon atoms in the longest chain: and here is the displayed formula for butanol: Summary of naming simple straight-chain organic molecules

The following table summarises the naming of some of the straight-chain alkanes, alkenes and alcohols, giving a name and a molecular formula for each:

Carbons in longest chainAlkanesAlkenesAlcohols
1methane, CH₄-methanol, CH₄O
2ethane, C₂H₆ethene, C₂H₄ethanol, C₂H₆O
3propane, C₃H₈propene, C₃H₆propanol, C₃H₈O
4butane, C₄H₁₀butene, C₄H₈butanol, C₄H₁₀O

Naming branched alkanes and alkenes

The naming conventions for organic molecules cover more than the straight chain molecules. Branched molecules are named depending on the number of carbon atoms in the branch. A branch with 1 carbon is called “methyl” and a branch with 2 carbons is called “ethyl”. This is similar to the conventions covered above, plus the “-yl-” bit just says it is a branch.

For example, this is the displayed formula for 2-methyl hexane: In the name 2-methyl hexane, the number 2 indicates that when counting along the longest carbon chain the methyl branch comes off the second carbon atom. The “methyl” bit of the name says there is one branch of 1 carbon. The “hex” bit of the name says the longest consecutive chain of carbon atoms is 6. The “ane” bit says the molecule has only single bonds.

When counting along the carbon atoms of the longest chain to work out the name, the numbering of carbon atoms starts from the end nearest to the branch. Another way to put this is that the name is given such that the numbers in the name are as low as possible. For example, here is the displayed formula for 4-ethyl octane: Another example, this time with 2 methyl branches coming off the second and third carbons of the chain, is 2,3-dimethyl hexane. The “di” in the name indicates there are two methyl groups. This is the same way in which “di” indicates there are two oxygen atoms in carbon dioxide. Another example of how the naming convention works for branches is 2,2-dimethyl hexane: This naming of branches also applies to alkenes. Here is the displayed formula of 4-methylpent-1-ene: ## 4:05 understand how to write the possible structural and displayed formulae of an organic molecule given its molecular formula

The molecular formula describes the actual number of each type of each atom in a molecule.

For example, a molecular formula of C₆H₁₂ tells us that in each molecule there are 6 carbon atoms and 12 hydrogen atoms.

However, the molecular formula tells us nothing about how those atoms are arranged. For example, it does not tell us if there any branches of carbon atoms coming off the main carbon-carbon chain, nor how long or how many there might be.

On the other hand, the structural formula and displayed formula of a molecule tell us clearly how the atoms are arranged in that molecule.

This means that if we are given a molecular formula only, there may be several possible structural and displayed formulae all of which could apply for that molecule.

When trying to work out possible structural or displayed formulae from a molecular formula there are several clues:

• If the molecular formula only has carbon and hydrogen in it, then of course the structural formula will only have atoms of these 2 elements.
• If the molecular formula has twice as many carbons as hydrogens (CnH2n) then the molecule is an alkene and has a double bond somewhere between 2 of the carbon atoms.
• If the molecular formula has two more than twice as many carbons as hydrogens (CnH2n+2) then the molecule is an alkane and only has single bonds.
• If the molecular formula has two more than twice as many carbons as hydrogens and also has an oxygen atom (CnH2n+2O), then the molecule is an alcohol, and somewhere in the displayed formula will be a carbon single-bonded to an oxygen which itself is then single-bonded to a hydrogen.

## 4:06 understand how to classify reactions of organic compounds as substitution, addition and combustion. Knowledge of reaction mechanisms is not required

In a substitution reaction an atom or group of atoms is replaced by a different atom or group of atoms. For example when ethane reacts with bromine gas one of the hydrogen atoms in ethane is substituted by one of the atoms of bromine from within the bromine molecule:

CH₃-CH₃         +         Br-Br         →         CH₃-CH₂Br         +         H-Br

ethane         +         bromine         →         bromoethane         +         hydrogen bromide

An addition reaction occurs when an atom or group of atoms is added to a molecule without taking anything away. For example when ethene reacts with bromine gas, the product is simply the addition of the two molecules:

CH₂=CH₂         +         Br-Br         →         CH₂Br-CH₂Br A combustion reaction is another way to say ‘burning’ and is a reaction with oxygen. Combustion of hydrocarbons with excess oxygen gives the products water and carbon dioxide, and also releases heat energy (exothermic reaction). Two examples the combustion of propane and the combustion of butene:

C₃H₈         +         5O₂         →         3CO₂         +         4H₂O

C₄H₈         +         6O₂         →         4CO₂         +         4H₂O

## 4:08 describe how the industrial process of fractional distillation separates crude oil into fractions

• Crude oil is separated by fractional distillation. • Crude oil is heated and the oil evaporates.
• The gas goes into the fractional distillation tower. As the gas rises the temperature falls.
• Fractions with higher boiling points condense and are collected nearer the bottom of the tower.

2023-01-10T08:34:25+00:00Categories: (b) Crude oil, 4 Organic chemistry, Edexcel iGCSE Chemistry||

## 4:09 know the names and uses of the main fractions obtained from crude oil: refinery gases, gasoline, kerosene, diesel, fuel oil and bitumen

Crude oil is separated into fractions by the process of fractional distillation.

FractionUse
Refinery gasesBottled gas
GasolineFuel for cars
KeroseneFuel for aeroplanes
Diesel OilFuel for lorries
Fuel OilFuel for ships
2023-01-10T08:34:49+00:00Categories: (b) Crude oil, 4 Organic chemistry, Edexcel iGCSE Chemistry||

## 4:10 know the trend in colour, boiling point and viscosity of the main fractions

The boiling point increases as the number of carbon atoms (chain length) increases.

The viscosity increases as the number of carbon atoms (chain length) increases.

The greater the number of carbon atoms (chain length), the darker in colour that fraction is.

The viscosity of a fluid describes how easily it flows. Water has a low viscosity, it flows very easily. Crude oil has a higher viscosity than water, it does not flow very easily.

Fractions (in order)Properties
Refinery gasesSmallest molecules. Lowest boiling point. Lowest viscosity. Lightest in colour.
Gasoline
Kerosene
Diesel
Fuel oil
BitumenLargest molecules. Highest boiling point. Highest viscosity. Darkest in colour.

2023-01-10T08:35:37+00:00Categories: (b) Crude oil, 4 Organic chemistry, Edexcel iGCSE Chemistry||

## 4:12 know the possible products of complete and incomplete combustion of hydrocarbons with oxygen in the air

Complete Combustion happens when there is enough oxygen available, producing carbon dioxide (CO2) and water (H2O) Incomplete Combustion happens when there is not enough oxygen available, with possible products being carbon monoxide (CO), carbon (C, soot), carbon dioxide (CO2) and water (H2O) 2023-01-10T08:35:55+00:00Categories: (b) Crude oil, 4 Organic chemistry, Edexcel iGCSE Chemistry||

## 4:13 understand why carbon monoxide is poisonous, in terms of its effect on the capacity of blood to transport oxygen references to haemoglobin are not required

Carbon monoxide may be produced from the incomplete combustion of fuels: Carbon monoxide is poisonous because it reduces the capacity of the blood to carry oxygen.

2023-01-10T08:36:04+00:00Categories: (b) Crude oil, 4 Organic chemistry, Edexcel iGCSE Chemistry||

## 4:14 know that, in car engines, the temperature reached is high enough to allow nitrogen and oxygen from air to react, forming oxides of nitrogen

When fuels are burned in vehicle engines, high temperatures are reached.

At these high temperatures nitrogen and oxygen from the air react to produce nitrogen oxides:

nitrogen          +          oxygen        →          nitrogen oxides

eg

N2 (g)              +          O2 (g)          →          2NO (g)

In the atmosphere these nitrogen oxides can combine with water to produce nitric acid (HNO3).

2023-01-10T08:36:12+00:00Categories: (b) Crude oil, 4 Organic chemistry, Edexcel iGCSE Chemistry||

## 4:15 explain how the combustion of some impurities in hydrocarbon fuels results in the formation of sulfur dioxide

Fossil fuels such as coal, gas and oil are derived from crude oil.

These fuels are hydrocarbons, but also include impurities such as sulfur.

When the fuels are burned, sulfur dioxide is produced which can escape into the atmosphere:

S (s)         +         O₂ (g)         →         SO₂ (g)

2023-01-10T08:36:20+00:00Categories: (b) Crude oil, 4 Organic chemistry, Edexcel iGCSE Chemistry||

## 4:16 understand how sulfur dioxide and oxides of nitrogen oxides contribute to acid rain

Acids formed in the atmosphere can fall as acid rain. This can be a major problem, killing trees and fish in lakes. The acid rain also corrodes limestone buildings and marble statues since these are both made of calcium carbonate (CaCO₃). Some metals such as iron are also attacked by acid rain.

Sulfur dioxide released into the atmosphere from the burning of fossil fuels can react with water and oxygen to make sulfuric acid (H₂SO₄):

2SO₂ (g)         +         2H₂O (l)         +         O₂ (g)         →         2H₂SO₄ (aq)

Also, if sulfur dioxide in the atmosphere reacts with just water, a weaker acid called sulfurous acid (H₂SO₃) is formed:

SO₂ (g)         +         H₂O (l)         →         H₂SO₃ (aq)

In car engines the temperature is high enough for the nitrogen in the air to react with oxygen to produce oxides of nitrogen, e.g:

N₂ (g)         +         O₂ (g)         →         NO₂ (g)

In the atmosphere these nitrogen oxides can produce nitric acid (HNO₃).

2023-01-10T08:36:29+00:00Categories: (b) Crude oil, 4 Organic chemistry, Edexcel iGCSE Chemistry||

## 4:17 describe how long-chain alkanes are converted to alkenes and shorter-chain alkanes by catalytic cracking (using silica or alumina as the catalyst and a temperature in the range of 600–700⁰C)

Cracking involves the thermal decomposition of long-chain alkanes into shorter-chain alkanes and alkenes: Conditions

Temperature: 600oC

Catalyst: aluminium oxide, Al2O3

2023-01-10T08:36:43+00:00Categories: (b) Crude oil, 4 Organic chemistry, Edexcel iGCSE Chemistry||

## 4:18 explain why cracking is necessary, in terms of the balance between supply and demand for different fractions

Cracking converts long chain hydrocarbons into short chain hydrocarbons.

Long-chain alkanes are broken down into alkanes and alkenes of shorter length.

Crude oil contains a surplus long chains.

Shorter chain hydrocarbons are in greater demand, e.g. petrol.

Cracking also produces alkenes which are used in making polymers and ethanol.

2023-01-10T08:36:51+00:00Categories: (b) Crude oil, 4 Organic chemistry, Edexcel iGCSE Chemistry||

## 4:19 know the general formula for alkanes

Alkanes have the general formula CnH2n+2

This means that to work out the number of hydrogens, you double the number of carbons and then add two.

2023-01-10T08:37:06+00:00Categories: (c) Alkanes, 4 Organic chemistry, Edexcel iGCSE Chemistry||

## 4:20 explain why alkanes are classified as saturated hydrocarbons

Saturated:   A molecule containing only single bonds between carbon atoms. For example, alkanes as described as saturated molecules.

Unsaturated:   A molecule containing a carbon-carbon double or triple bond. For example, alkenes as described as unsaturated molecules.

2023-01-10T11:03:36+00:00Categories: (c) Alkanes, 4 Organic chemistry, Edexcel iGCSE Chemistry||

## 4:21 understand how to draw the structural and displayed formulae for alkanes with up to five carbon atoms in the molecule, and to name the unbranched-chain isomers The displayed formulae show all the atoms and bonds drawn out.

The molecular formulae just show the number of each type of atom in the molecule.

2023-01-10T11:04:20+00:00Categories: (c) Alkanes, 4 Organic chemistry, Edexcel iGCSE Chemistry||

## 4:23 know that alkenes contain the functional group >C=C<

Alkenes are a homologous series of hydrocarbons which contain a carbon-carbon double bond. This double bond is shown in formulae as a double line.

The names of alkenes end with “ene”.

An example is ethene, the structural formula for which is CH₂ = CH₂

For a molecule with more than two carbon atoms, the position of the double bond within the molecule can vary as indicated by the name and the structural formula.

2023-01-10T11:04:31+00:00Categories: (d) Alkenes, 4 Organic chemistry, Edexcel iGCSE Chemistry||

## 4:25 explain why alkenes are classified as unsaturated hydrocarbons

Saturated:   A molecule containing only single bonds between carbon atoms. For example, alkanes as described as saturated molecules.

Unsaturated:   A molecule containing a carbon-carbon double or triple bond. For example, alkenes as described as unsaturated molecules.

2023-01-10T11:05:04+00:00Categories: (d) Alkenes, 4 Organic chemistry, Edexcel iGCSE Chemistry||

## 4:26 understand how to draw the structural and displayed formulae for alkenes with up to four carbon atoms in the molecule, and name the unbranched-chain isomers. Knowledge of cis/trans or E/Z notation is not required The displayed formulae show all the atoms and bonds drawn out.

The molecular formulae just show the number of each type of atom in the molecule.

2023-01-10T11:05:17+00:00Categories: (d) Alkenes, 4 Organic chemistry, Edexcel iGCSE Chemistry||

## 4:44 know that an addition polymer is formed by joining up many small molecules called monomers One bond in the double bond breaks.

Monomers join together to form a long chain.

Polymer contains only single bonds.

## 4:45 understand how to draw the repeat unit of an addition polymer, including poly(ethene), poly(propene), poly(chloroethene) and (poly)tetrafluroethene            ## 4:46 understand how to deduce the structure of a monomer from the repeat unit of an addition polymer and vice versa

To deduce the structure of the monomer from a repeat unit:

1. Remove the extending single bonds
2. Draw in a double bond   Here’s a more complicated example, going from the polymer to the structure of the monomer Select a set of flashcards to study:

Terminology

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Section 1: Principles of chemistry

a) States of matter

b) Atoms

c) Atomic structure

d) Relative formula masses and molar volumes of gases

e) Chemical formulae and chemical equations

f) Ionic compounds

g) Covalent substances

h) Metallic crystals

i) Electrolysis

Section 2: Chemistry of the elements

a) The Periodic Table

b) Group 1 elements: lithium, sodium and potassium

c) Group 7 elements: chlorine, bromine and iodine

d) Oxygen and oxides

e) Hydrogen and water

f) Reactivity series

g) Tests for ions and gases

Section 3: Organic chemistry

a) Introduction

b) Alkanes

c) Alkenes

d) Ethanol

Section 4: Physical chemistry

a) Acids, alkalis and salts

b) Energetics

c) Rates of reaction

d) Equilibria

Section 5: Chemistry in industry

a) Extraction and uses of metals

b) Crude oil

c) Synthetic polymers

d) The industrial manufacture of chemicals

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