gce o level orgo and hydrogen stuff

what is a macromolecule

a large molecule made up of many atoms with numerous strong covalent bonds

what is a monomer

small molecules that join together to form a long chain molecule

what is a polymer

a large long chain molecule formed by the joining of many small molecules

what is addition polymerisation

the reaction process of many small molecules (monomers) joining together to form a large long chain molecule as its only product (polymer)

what are fossil fuels

• they are formed under high temp and pressure from the remains of plants and animals that died millions of years ago

• eg coal

• eg petroleum/crude oil — 1. mixture of hydrocarbons, mostly alkanes and some alkenes 2. must be refined/separated into fractions before it can be used

• eg natural gas — 1. found above petrol in ground 2. methane is the main constituent of natural gas

why is fractional distillation of crude oil important in real life

it separates hydrocarbons into useful fractions for daily life eg fuel or chemical feedstock for manufacture of plastic

how is crude oil separated into useful fractions

1. crude oil is heated to a high temperature until it boils and vapourises

2. temperature is hotter at bottom of column than the top

3. the vapour rises, cools and condenses and the process repeats

4. heavier fractions have higher boiling points and condenses at the bottom

what is cracking

1. breakdown or decomposition of large alkane molecules into smaller molecules

2. total number of carbon and hydrogen atoms remain the same after cracking

3. alkanes and sometimes hydrogen is formed

why is cracking important

1. crude oil contains more of the heavier fractions than the lighter fractions

2. lighter fractions are in higher demand as they are more useful as fuels

3. Hence heavier fractions are converted into lighter fractions to meet demand

uses of cracking

• production of alkenes for alcohol and plastic

• production of hydrogen for ammonia and fuel

two types of cracking

1. steam cracking — use of high temp

2. catalytic cracking — use of high temp (but lower) + catalyst (eg aluminium oxide/silicon dioxide)

why can’t we make pure ethanol using only fermentation

• yield is only about 12-15%

• at this concentration of ethanol, enzymes in yeast denature → stops fermentation reaction

how to separate ethanol and water?

fractional distillation

1. when heating mixture, ethanol vapour and water vapour rises up the column

2. water (higher bp) condenses and drips back into flask

3. ethanol (lower bp) reaches upper part of column and enters condenser

4. ethanol vapour condenses and liquid ethanol is collected → higher concentration of ethanol is obtained

5. concentration of ethanol in conical flask decreases over time

products formed from combustion of alcohol

CO2 and water

uses of alcohol

• alcohol drinks

• biofuels for cars

yay and nay of biofuels

yay

1. net carbon dioxide emissions are lower for biofuel than fossil fuels because ethanol is carbon neutral since the carbon dioxide released during combustion is absorbed by plants during photosynthesis

2. sugar plant is a renewable source but crude oil isn’t

3. since alcohol burn more cleanly, combustion of ethanol does not release harmful pollutants like soot

nay

1. fermentation for ethanol is a time consuming process

2. ethanol releases less energy per litre than petrol

3. sugar cane growth is unreliable and slow compared to crude oil supply

4. fewer food crops would be available since they’re used for biofuels instead of food

what are isomers

organic molecules with the same molecular formula but different structural formula

physical methods to recycle plastic

grind plastic into smaller pieces, then melt, cool, pull into thin long strands, and cut into pellets for new products

chemical methods to recycle plastics

1. cracking

   • large long chain alkanes eg polyethene is cracked to form short chain of alkanes and alkenes to be used as fuels and chemical feedstock respectively

2. depolymerisation

   • polymers are broken down into their monomers to be converted into other useful chemicals

what happens during polymerisation

polyesters undergo acid hydrolysis by reacting with water in the presence of an acid catalyst to form the monomers diol and dicarboxylic acid

yay and nay of recycling plastic

yay

1. economic — recycling uses significantly less fossil fuels than the amount used for new plastic production

2. environmental — reduces air pollution that is caused by burning waste

nay

1. economic — recycled plastics have a lower market value than virgin plastics made from raw materials

2. environmental — washing plastics during pre-treatment may result in the release of microplastics into water

what are fuels

substances that burn easily in air to produce energy

how does hydrogen act as a fuel

burns in oxygen to form water — exothermic reaction (combustion)

what is a fuel cell

a device in which a fuel (eg hydrogen) reacts with the oxygen (to form water) in the air to generate electrical energy directly (without combustion)

yay and nay of using hydrogen fuel cells compared to fossil fuels

yay

1. water is the only product + non-polluting compared to petrol engines which produce carbon dioxide, exacerbating global warming

2. more energy is released per gram of hydrogen

3. more efficient since hydrogen fuel cells directly convert chemical energy into electrical energy

4. hydrogen obtained from seawater is a renewable fuel but petrol is not

nay

1. hydrogen is potentially explosive

2. hydrogen and oxygen are extracted using fossil fuels

composition of gases in air

nitrogen — 78%

oxygen — 21%

noble gases — 1% (mainly argon)

carbon dioxide — 0.03%

water vapour — variable

when testing for percentage of oxygen in air, why must we keep heating until volume remains constant

ensure all oxygen in air reacts with copper

what precaution should be taken before finding volume of air

ensure setup is cooled to room temp bc gases occupy a larger volume at higher temp due to expansion

how is oxygen formed in the lab

• decomposition of hydrogen peroxide catalysed by manganese(IV) oxide (2H2O2 → 2H2O + O2)

• first few test tubes of collected gas should be rejected bc the oxygen would be contaminated by nitrogen

how is oxygen obtained industrially

fractional distillation of liquid air

how does carbon cycle regulate carbon dioxide in atmosphere

• rate of removal of CO2 must be balanced by rate of production of CO2

• combustion and respiration produce CO2, photosynthesis removes CO2

sources of greenhouse gases

methane

• bacterial decay of vegetable matter or cow flatulence

carbon dioxide

• burning/combustion of fossil fuels

consequences of increase in global warming

• CO2 is produced at a rate faster than it is removed by photosynthesis → global warming

• melting of polar ice caps → flooding of low-lying land

carbon monoxide pollutant

source: incomplete combustion of carbon-containing substances like petrol in insufficient supply of oxygen

effect: a poisonous gas that binds haemoglobin and prevents it from transporting oxygen around body

solution: cars are fitted with catalytic converters to oxidise carbon monoxide to harmless carbon dioxide

nitrogen oxides pollutant

source:

• lightning activity — heat energy released by lightning causes nitrogen and oxygen in the air to react and form nitrogen oxide and nitrogen dioxide

• internal combustion engines of cars — nitrogen and oxygen in the air react at high temperature to form nitrogen oxide and nitrogen dioxides in internal combustion engines of cars

effect:

• dissolves in rain to form acid rain which corrodes limestone buildings and metallic structures (2 NO2 + 3 O2 + 2 H2O → 4 HNO3)

• causes breathing difficulties

solution: cars are fitted with catalytic converters which reduces the nitrogen oxide to harmless nitrogen (2 CO + 2 NO → 2 CO2 + N2)

unburnt hydrocarbons pollutant

source: incomplete combustion of fuels in internal combustion engines of cars

effect: reacts with nitrogen oxides to produce ozone

treatment: catalytic converters convert unburnt hydrocarbons to form carbon dioxide and water

sulfure dioxide pollutant

source:

• combustion of fossil fuels which contain sulfur compounds

• volcanic eruptions

effect:

• dissolves in rain to form acid rain which corrodes limestone buildings and metallic structures (2 SO4 + O2 + 2 H2O → 2 H2SO4)

• causes breathing difficulties

treatment:

• flue gases containing sulfur dioxide are removed by being treated with calcium carbonate (CaCO3 + SO2 → CaSO3 + CO2)

• this process is known as flue-gas desulfurisation

ozone low altitudes pollutant

source: in sunlight nitrogen oxides react with unburnt hydrocarbons to produce ozone which is the main component of smog

effect:

• causes breathing difficulties especially for asthma sufferers

• slows down photosynthesis in plants which can damage crops

treatment: reduce emissions of unburnt hydrocarbon fuels

what is ozone

• O3

• allotrope of oxygen (different forms of the same element with different arrangement of atoms)

why is ozone at high altitudes important

surrounds earth and prevents excessive harmful ultra-violet rays emitted by the Sun from reaching earth

what are CFCs

chlorofluorocarbons are compounds of chlorine, fluorine, and carbon

what is causing the depletion of ozone in the stratosphere

1. UV rays break the C-Cl bonds in CFCs to form chlorine atoms

2. C-F bonds are not broken because energy from UV rays is not strong enough

3. Cl atoms catalyse the breakdown of ozone in a two-step reaction

4. chlorine atoms react with ozone to form chlorine monoxide, which reacts with more ozone, regenerating Cl atoms that is chemically unchanged (2 O3 → 3 O2)

how do chlorine atoms act as a catalyst for breakdown of ozone

• for every chlorine atom used up as it reacts with 1 ozone molecule, 1 chlorine atom is regenerated in another reaction

• it is then recycled where it reacts with another ozone molecule

• 1 chlorine atom continues destroying thousands of ozone molecules

consequences of ozone depletion

excessive harmful UV rays can lead to increased risk of skin cancer, eye cataracts, and damage to food crops

how can we slow down the depletion of the ozone layer

switch to alternative sources of energy eg electric cars, biofuel that produces less unburnt hydrocarbons

what is kinetic particle theory

all matter is made up of small countable particles that are in constant random motion