Hydrocarbons

Question 1

why is carbon important and what is organic chemistry?

Answer 1

90% of compounds contain carbon.
Compounds containing carbon are the basis of all living things.
Organic chemistry is the chemistry of all compounds containing carbon (except carbonates and hydrogen carbonates).

Question 2

what are hydrocarbons and are they polar or non-polar?

Answer 2

Only contain hydrogen and carbon.

Non-polar because there is no great difference between them.

Question 3

what is crude oil and how is it formed? how is it used? What changes does it undergo? What does this create and what are they used for?

Answer 3

Fossil fuels come from plant and animal remains.
Over million years it has been affected by high temperatures and pressures and have become hydrocarbons.
A mixture of hydrocarbons is called crude oil.
Not used in raw state.
Undergoes fractional distillation which separates it into different components called fractions.
The fractions have similar boiling points and molecular masses.
Fractions are used as fuels.
Heavier fractions are broken down to smaller more useful molecules in a process called cracking.

Question 4

what are homologous series? what are three?

Answer 4

Hydrocarbons are grouped into families that have similar structures and properties but differ in size.
A family is called a homologous series.
Three are alkanes, alkenes and alkynes.

Question 5

what are alkanes? polarity? solubility? what forces hold them together? what is the first in the series? saturation?

Answer 5

Joined by single covalent bonds.
Remaining bonds are to hydrogen.
Non-polar.
Insoluble in water.
Only intermolecular force is dispersion forces.
First in the series is methane.
Naming system has been developed with prefixes that indicate the number of carbons. Alkanes are unsaturated hydrocarbons- only single bonds between carbons and therefore have a max number of hydrogens around each carbon.

Question 6

what are the prefixes?

Answer 6

meth-
eth-
prop-
but-
pent-
hex-
hept-
Oct-
Non-
Dec-

Question 7

what is the general formula for alkanes?

Answer 7

Cn H2n + 2

Question 8

how reactive are alkanes? what reactions they undergo?

Answer 8

Fairly un reactive but used for fuel.
Reaction between hydrocarbon and oxygen is a combustion reaction.
If oxygen supply is plentiful carbon dioxide and water will be produced- complete combustion.

Question 9

what are semi-structural or condensed formulas?

Answer 9

Semi-structural formula or condensed structural formula- symbols without lines.

Question 10

what are structural isomers?

Answer 10

Some molecular formula but different structures

Question 11

how can isomers differ in boiling temperature?

Answer 11

Both non-polar therefore both have dispersion forces holding them together.
One is linear which means the molecules can get closer together making the dispersion forces stronger. This is why a linear one has higher boiling and melting temperatures than a branched one.

Question 12

what are the 6 steps for naming branches?

Answer 12

Identify the longest unbranched carbon chain.
Number the carbon atoms in the chain from the end that will give the smallest number to branching groups.
Name the alkyl groups after the alkane from which they derived.
Place the number and position of each of the alkyl groups at the beginning of the name.
If two identical chains are present, use di- or tri- for three.
If there are alkyl side chains of different length on the molecules, list them in alphabetical order at the start of the name, with their numbers to indicate their respective positions.

Question 13

what are alkenes? what is the first one? what is their polarity and solubility and how is their bond indicated in the name?

Answer 13

Ethene is the first member of the homologous series containing one carbon to carbon double bond.
Hydrocarbons that have multiple bonds between carbons are called unsaturated.
They are non-polar and do not dissolve in water.
The position of the double bond is indicated with a number.

Question 14

how do alkenes undergo combustion reactions?

Answer 14

Undergo complete combustion when there is plenty of oxygen.

Alkene + oxygen ——> carbon dioxide + water

Question 15

how do alkenes undergo addition reactions?

Answer 15

Readily under go these reactions.

Lose their double bond to form a saturated molecule.

Question 16

how can an alkene be tested?

Answer 16

If a substance reacts with bromine (orange) and bromine loses its colour, it is an alkene, if not, it is a saturated molecule and no change occurs.

Question 17

what are alkynes and what is the simplest one?

Answer 17

One triple carbon-carbon bond.

The simplest is ethyne: C2H2

Question 18

what is the formula for alkynes?

Answer 18

CnH2n - 2

Question 19

what are cyclic and aromatic compounds? what are they made up of? what is their structure based on? what are some properties? what are their bonds like? saturation? what are they used for?

Answer 19

A chain of carbons in a ring (cyclic).
Aromatic compounds have aromas.
The structure is based on a benzene ring C6H6- simplest aromatic compound.
non-polar solvent.
Toxic.
Used to manufacture polymers, drugs and dyes
Benzene is a planar molecule.
Each carbon-carbon bond is identical and has properties consistent with a bond half way between a double and single bond.
Benzene is unsaturated.

Question 20

what is a planar molecule?

Answer 20

All molecules with angular; trigonal or lineal geometries

Question 21

what are properties of hydrocarbons with reference to methane, propane, petrol and lubricating oils? which ones are gases, liquids or solids. How do boiling points change and what is volatility?

Answer 21

Methane is a colourless, odourless and tasteless gas.
Major component of natural gas.
Propane and butane are the main components of bottled gas.
Petrol is a mixture of many hydrocarbons.
Lubricating oils and waves have much longer carbon chains.
C1-C4 are gases
C5-C15 are liquids
C16 onwards are solids
Boiling point increases with number of carbons but volatility decreases.
volatility: a measure of how easily liquids evaporate.
The vapour above the liquids is the bit that burns- more volatile, more flammable.

Question 22

why do boiling temperatures increase as the molecular size of alkanes increase?

Answer 22

Larger molecules have more electrons and therefore greater dispersion forces which take more energy to overcome.

Question 23

why are larger molecules more viscous?

Answer 23

Larger molecules are more viscous or thick because the long chains become tangled.

Question 24

how are alkenes and alkanes similar in trends?

Answer 24

Alkenes follow similar trends to alkanes but with slight variation between the alkane and the alkene with the same number of carbons.

Question 25

does propane or propene have higher boiling point?

Answer 25

Propane as it is slightly longer and more electrons mean greater dispersion forces.

Question 26

what are alcohols defined by? what is a functional group? what is the simplest one?

Answer 26

Contain the hydroxyl, -OH, a functional groups (an atom or group of atoms that gives a molecule its characteristic properties).
The simplest is methanol.

Question 27

what is ethanol? what is its polarity and solubility?

Answer 27

Ethanol is the second and is less toxic and the intoxicating part of alcohol. It is a useful solvent as it is fairly polar.
Soluble in water mainly because of the polar hydroxyl functional group which can hydrogen bond with water.

Question 28

how does solubility of alcohols change?

Answer 28

As the non-polar hydrocarbon ends become larger in propanol etc. they become less soluble as their polar nature decreases.

Question 29

why do alcohols have higher boiling points than alkanes?

Answer 29

They have higher boiling points than corresponding alkanes because of the hydrogen bonding.

Question 30

how are isomers of alcohols named?

Answer 30

The position of the alcohol group must be shown in the name eg. Propan-1-ol

Question 31

what are carboxylic acts identified by? what is their formula?

Answer 31

Identified by the presence of a carboxyl group (-COOH).

The general formula is RCOOH (R is an alkyl group).

Question 32

what are carboxylic acids? what are their properties?

Answer 32

Weak organic acids.
Ethanoic acids is also called acetic acid.
Carboxylic acids are capable of hydrogen bonding and thus have relatively high melting temps. (higher than a corresponding alcohol).
Carboxylic acids are more soluble in water than alcohol and solubility decreases with size.

Question 33

how are carboxylic acids named?

Answer 33

Oic ending

When naming, the carboxyl group is always placed on carbon one.

Question 34

what are esters and what are some properties?

Answer 34

Characteristic odours.
Low boiling points so they can evaporate easily.
Even though they are polar they cannot hydrogen bond and therefore have low boiling points.

Question 35

how are esters made?

Answer 35

Made from a condensation reaction between a carboxylic acid and an alcohol- esterification reaction

Question 36

how are esters named?

Answer 36

First part comes from the alcohol and ‘anol’ is replaced with ‘yl’.
Second part comes from the carboxylic acid- replace ‘oic acid’ with ‘oate’.

Question 37

what are structural isomers of esters?

Answer 37

The position of the ester group can change- an isomer.

Question 38

what are polymers and what are they made of? what is their structure? how do they change? what does the type of polymer depend on? what are the two main types?

Answer 38

Large covalent molecules.
Made up of smaller molecules called monomers.
Have carbon backbones but may have other elements on them.
Not all are the same length- size depends on the number of monomers and formula does not change.
Two main types: addition polymers and condensation polymers.
type of polymer depends on type of monomer,

Question 39

what are addition polymers?

Answer 39

Formed from unsaturated monomers where the double bond between carbons reacts to form a new covalent bond between monomers.

Question 40

how are polymers named?

Answer 40

Name of the monomer with the prefix ‘poly’.

Question 41

how do properties of polymers change? and what are non-polar bonds?

Answer 41

Properties depend on bonding between chains.

Non-polar bonds are dispersion forces- weak so soft and easily melted and moulded.

Question 42

what is high density polythene? how is it made? what is it used for?

Answer 42

Produced at low pressures with a catalyst, the chain has few side branches.
Packs chains together closely.
High density and rigid.
Forms piping, containers etc.

Question 43

what is LDPE? how is it made? what is it used for?

Answer 43

Produced at high temperatures with a catalyst.
Frequent side branches.
Chains cannot pack closely.
Low density, soft and flexible. 
Garbage bags, cling wrap, garden tubing.

Question 44

what is a thermoplastic? what are its properties?

Answer 44

Classified on basis of thermal behaviour (reaction to heat).
Plastics which may be repeatedly melted, reshaped and hardened by cooling are thermoplastics polymers.
Strong covalent bonds within but weak forces between.
Weak forces break, molecules move more freely and polymers softens.
Soft and flexible.

Question 45

what are thermosetting polymers? what are their properties?

Answer 45

Do not melt but char.
Rigid due to strong covalent bonds within and between.
Covalent bonds between are called cross links.

Question 46

what are elastomers? how do they regain shape?

Answer 46

Regain shape when stretched or pulled.
Small number of cross links prevent chains slipping past each other.
Less crosslinks than thermosetting polymers but even a small number of links enables it to return to shape.
By controlling the number of cross links we control elasticity.