chem 7

what is a hydrocarbon

organic compound containing hydrogen and carbon only

what is the homologous series

a group of organic compounds that react in a similar way

what is a alkane n general formula

C-C single bond

CnH2n+2

they r saturated compounds - each carbon atom forms 3 single covalent bonds

part of homologous series

first 4 alkanes

methane, ethane, propane, butane

what properties change as the hydrocarbon chain gets longer

1. the shorter the chain, the less viscous it is

2. the shorter the more volatile the hydrocarbon is - eg lower BP

3. the shorter the carbon chain, the more flammable it is

when does complete combustion occur

when theres plenty of oxygen

formula for complete combustion

hydrocarbon + oxygen →carbon dioxide + water

why are hydrocarbons used at fuels

due to the amount of energy released when they combust completely

what is crude oil and hows it formed

a fossil fuel, formed from the remains of plants and animals, mainly plankton that died millions of years ago and were buried in mud

over millions of year, w high temperature and pressure, the remains turn to crude oil

It is a mixture of lots of different hydrocarbons, most of which r alkanes

how does fractional distillation work

1. oil is heated until most turned into a gas, the gases enter a fractional column (the liquid bit is drained off)

2. theres a temperature gradient in the column (hot at bottom and gets cooler as u go up)

3. LONGER hydrocarbons have high BP and they condense into liquids and drain out of the column early on at the bottom. The SHORTER ones have lower BP and condense and drain out later on, near top of column

4. u end up w the crude oil mixture separated out into different fractions, each fractions contains a mixture of hydrocarbons that contain a similar number a carbon atoms n similar BP

crude oil uses in modern life

1. fuel for most modern transport - diesel oil, kerosene, heavy fuel oil and LPG (liquid petroleum gas)

2. the petrochemical industry uses some of the hydrocarbons from crude oil as a feedstock to make new compounds for things like polymers, solvents, lubricants and detergents

what r organic compound

compounds containing carbon atoms

what is cracking and why good

splitting up long chain hydrocarbons

1. short chain hydrocarbons r flammable so make good fuels and are in high demand and long chain ones form thick gloopy liquids which r not as useful

2. cracking also produces another type of hydrocarbon, alkenes - they r used as a starting material when making lots of other compounds and to make polymers

what type of reaction is cracking

thermal decomposition reaction - breaking molecules down by heating them

heating long chain hydrocarbons to vaporise them

what is catalytic cracking

the vapour is passed over a hot powdered aluminium oxide catalyst

the long-chain molecules split apart on the surface of the specks of catalyst

what is steam cracking

mix them w steam and then heat them to a v high temp

what is the petrochemical industry

The petrochemical industry uses fractions from crude oil to make chemicals such as polymers, solvents, detergents and fuels.

2 methods used by the petrochemical industry for cracking hydrocarbons

Catalytic cracking

• hydrocarbons are heated

• passed over a catalyst

• makes smaller alkanes and alkenes

Steam cracking

• hydrocarbons are heated with steam

• also breaks them into smaller molecules

alkenes and characteristics

have a C=C bond

have a double bond between 2 of the carbon atoms in their chain

it means that alkenes have 2 fewer hydrogens compared w alkanes containing the same number of carbon atoms, making them unsaturated

alkenes general formula

CnH2n

what makes alkenes more reactive alkanes

the double C=C bond can open up to make a single bond, allowing the 2 carbon atoms to bond w other atoms

first 4 alkenes

ethene, propene, butene, pentene

how do alkenes burn and why

with a smoky flame

when burnt in air they tend to undergo incomplete combustion

CO2 and H2O are still produced but u can also get carbon and carbon monoxide (CO) which is poisonous

incomplete combustion formula

alkene + oxygen → carbon + carbon monoxide + co2 + water

• results in a smoky yellow flame and less energy being released compared to complete combustion

how to alkenes react

via addition reactions

all have functional group C=C, so they all react in similar ways and u can suggest products of a reaction based on how alkenes react in general

• the carbon-carbon double bond will open up to leave a single bond and a new atom is added to each carbon

what is addition of a hydrogen called

hydrogenation

• hydrogen can react w the double-bonded carbons to open up the double bond and form the equivalent, saturated, alkane

what can alkenes also react with

halogens - bromine, chlorine and iodine

the molecules formed are saturated w/ the C=C carbons each becoming bonded to a halogen atom

what do alkenes do to bromine water

turn it from orange to colourless

• alkanes have no effect, only alkenes

what does steam react with alkenes to form

alcohols

when alkenes react with steam, water is added across the double bond and an alcohol is formed

how is ethanol produced from ethene and steam

1. Ethene reacts with steam in the reactor to produce ethanol.

• Word equation: ethene + steam → ethanol

2. The reaction mixture then passes into a condenser, where it is cooled.

3. Ethanol and water condense into liquids because they have higher boiling points.

4. Unreacted ethene does not condense because it has a lower boiling point, so it stays as a gas.

5. The unreacted ethene is recycled back into the reactor so it can react again.

• This reduces waste and improves yield.

6. The liquid mixture still contains ethanol and water, so they are separated by fractional distillation.

7. Ethanol is collected first because it has a lower boiling point than water.

what are plastic made of

long chain molecules, polymers

formed when lots of small monomers join together

usually carbon based w/ alkene monomers

what is polymerisation

when lots of small molecules, monomers, join together to form a long molecule, a polymer

what r addition polymers made from

unsaturated monomers

1. the monomers that make up addition polymers have a double covalent bond

2. lots of unsaturated monomer molecules, alkenes, can open up their double bonds and join together to form polymers chains - this is addition polymerisation

what does addition polymerisation require

high pressure and a catalyst

what are alcohols and their general formula

-OH group

general formula:

first 4 alcohols

methanol, ethanol, propanol, butanol

alcohol charcteristics

flammable and undergo complete combustion is air to produce CO2 and water

all soluble in water and their solutions have a neutral pH

also can react w/ sodium, one product of this is hydrogen

what happens when alcohols r heated

they are flammable

complete combustion

produce CO2 and WATER

what do different alcohols form

different carboxylic acids

what are alcohols used as and examples

solvents and fuels

• methanol and ethanol used as solvents in industry this is bc they can dissolve most things water can dissolve as well as substances that water cannot dissolve

• first 4 alcohols used as fuels bc they burn cleanly and not smelly

what is ethanol made by and for what

fermentation for alcoholic drinks such as wine or beer

uses an enzyme in yeast to convert sugars into ethanol, co2 also produced

• happens fastest at 37 degrees in a slightly acidic solution and under anaerobic condtions

fermentation word equation

sugar →ethanol + carbon dioxide

→is yeast

carboxylic acids functional group

-COOH

first 4 carboxylic acids

methanoic, ethanoic, propanoic, butanoic

how do carboxylic acids react

like any other acid, with carbonates to produce salt, water and carbon dioxide

what happens when carboxylic acids dissolve in water

they ionise and release H+ ions resulting in an acidic solution

but they don’t ionise completely, so form weak acidic solutions

have a high pH (less acidic) than aqueous solutions of strong acids with the same concentration

esters functional group and how formed

-COO-

formed from an alcohol and a carboxylic acid

an acid catalyst is usually also used

how are esters made from carboxylic acids

alcohol + carboxylic acid →ester + water

→is acid catalyst

example of 1 ester

ethyl ethanoate

how r polymers made by condensation polymerisation

involves monomers which contain different functional groups

the monomers react together and bonds form between them, making polymer chains

for each new bond that forms, a small molecule (water) is lost

THIS IS WHY ITS CALLED CONDENSATION POLYMERISATION

how r addition and condensation polymerisation different

addition:

• only 1 monomer type containing a C=C bond

• only 1 product formed

• functional groups involved in polymerisation: carbon-carbon double bond in monomer

condensation

• 2 monomer types each containing 2 of the same functional groups OR one monomer type with 2 different functional groups

• 2 types of product - the polymer and a small molecule (water)

• functional groups involved in polymerisation: 2 reactive groups on each monomer

3 naturally occurring polymers

proteins (amino acids)

DNA molecules (nucleotide polymers)

simple sugars (eg starch or cellulose)

what 2 groups do amino acids have

amino group (NH2) and an acidic carboxyl group (COOH)

example of amino acid

glycine

how do amino acids form proteins

1. they form polymers known as POLYPEPTIDES via condensation polymerisation

• the amino group of an amino acid can react with the acid group of another, and so on, to form a polymer chain. For every new bond formed, a water molecule is lost

2. 1 or more long chains of polypeptides are known as PROTEINS

3. the order of the amino acids in their polymer chains is what gives proteins their properties and shapes

what r dna molecules made from and how

nucleotide polymers

• dna found in every living thing, contains genetic info, it is large and double helix shaped

1. DNA is made of 2 polymer chains of monomers called nucleotides. each contains a small molecule, a base, 4 different types of bases (A, C, G, T)

2. the bases on the different polymer chains pair up with eachother and form cross links keeping the 2 strands of nucleotides together, and making it double helix shaped

3. order of bases = code of an organisms genes

how do simple sugars form polymers

sugars are small molecules that contain carbon, oxygen and hydrogen

sugars react together through polymerisation reactions to form larger polymers, like starch which living things use to store energy, and cellulose found in plant cells

Explain how oxides of nitrogen are produced when burning fuels.

high temperatures ignore pressure

(cause) nitrogen (from air) and oxygen (from air) to react

In the first step, crude oil is heated and hydrocarbon vapours are formed.

Explain how kerosene is produced from these hydrocarbon vapours.

there is a temperature gradient in the (fractionating) column

(so) kerosene condenses

at the level (in the column) corresponding to kerosene’s boiling point (range)

Explain how fractions are obtained from crude oil by fractional distillation.

crude oil is heated to vaporise (the hydrocarbons)

there is a temperature gradient in the (fractionating) column

(so) the gases condense at different levels

because of their) different boiling points

Explain why sulfur impurities are removed before petrol is burned in car engines.

(when burned sulfur impurities) produce sulfur dioxide

(which) causes acid rain

Name the process which produces smaller hydrocarbon molecules from heavy fuel oil.

Give the conditions used in this process.

(name of process) cracking

(conditions) high temperature

steam / catalyst

Give the result of the test when carbon dioxide is bubbled through limewater.

calcium hydroxide

method to show different dyes in an ink

draw pencil start line

• place spot of ink on start line

• name suitable solvent

• place solvent in beaker

• place paper in solvent so solvent is below start line

• use a lid

• allow solvent / dyes to travel up paper (until near top)

• dry + count spots

Give the general name for what dna is made of

nucleotides