Intro to organic chemistry and alkanes Flashcards
What is the general formula of alkanes?
CnH2n+2
What is the general formula of alkenes?
CnH2n
What is the general formula of cycloalkane?
CnH2n
What does the term empirical formula mean?
Simplest whole number ratio of the number of atoms of each element in a substance
State two features of a homologous series (3)
Members of a homologous series have very similar chemical properties
They have the same functional group
Members will show a change in physical properties like increasing boiling point as the carbon chain gets longer
What are structural isomers?
Molecules with the same molecular formula but different structural formula
What are the three types of structural isomerism?
Positional, chain, functional isomerism
What is stereoisomerism?
Molecules with the same structural formula but a different arrangement of atoms in space
For a molecule to have E/Z isomerism, what must a molecule have?
A double bond which restricts rotation
Each carbon in the double bond must have two different groups attached
What are hydrocarbons?
Compounds that only contain carbon and hydrogen
When does the boiling point increase in alkanes? (3)
Boiling point increases as the carbon chain length increases
There are more electrons
So stronger Van der Waals between molecules
When branching increases but number of electrons stay the same, why does the boiling point decrease? (2)
Because less surface area so weaker Van der Waals between molecules
Name a process for separating an alkane from a mixture of compounds
Fractional Distillation
Outline process of fractional distillation of crude oil (5)
Crude oil is passed into a fractionating column
The column is very hot near the base but much cooler near the top
The mixture starts to boil and rise and condenses at the tray with its boiling point
The larger hydrocarbons, with higher boiling points, will condense first near the base of the column
The smaller hydrocarbons, with lower boiling points, will condense last near the top of the column
How does fractional distillation work? (2)
By breaking the intermolecular forces between molecules, the molecules themselves are unaffected by this process
What are fractions? (1)
Mixture of hydrocarbons with similar boiling points
Outline the essential features of the fractional distillation of crude oil that enable the crude oil to be separated into fractions (4)
All the hydrocarbons have different boiling points
Boiling point depends on the length of compound
It is hotter near the bottom of the column
Heavier molecules condense at the bottom
Explain why oil companies need to crack ‘heavy fractions’ (1)
High demand for shorter chain alkanes and alkenes
What are the products of thermal cracking? (2)
Two alkenes (higher percentage of alkenes) and one alkane
What are the conditions needed for thermal cracking? (2)
High temperature: 700 - 1200K
High pressure: 7000kPa
What are the products of catalytic cracking? (3)
High percentage of branched alkanes and cycloalkanes and aromatic hydrocarbons
What type of cracking is more efficient and cheaper?
Catalytic Cracking
What are the conditions needed for catalytic cracking? (3)
High temperature: 720K
Slight Pressure: 100kPa
Catalyst: zeolite
What do catalytic converters catalyse and why are they used? (3)
Catalyse these reactions of products from car exhausts:
2CO + 2NO —> N2 + 2CO2
hydrocarbon + NO —> N2 + CO2 + H2O
What is combustion? (2)
The process of burning something
A reaction with oxygen
When does complete combustion occur? (1)
When there is plenty of oxygen
What is the equation for complete combustion? (1)
hydrocarbon + oxygen –> carbon dioxide + water
When does incomplete combustion occur? (1)
When there is a limited supply of oxygen
What is the equation for incomplete combustion? (2)
Hydrocarbon + oxygen –> carbon monoxide + water
Hydrocarbon + oxygen –> carbon + water
All hydrocarbon-based fuels derived from crude oil may produce pollutants when they are combusted. What do these pollutants include? (4)
Carbon dioxide
Water vapour
Carbon monoxide
Carbon particles
How is sulphur dioxide produced from burning fuels (1)
S(s) + O2 (g) –> SO2 (g)
Environmental impact of sulphur dioxide? (2)
Dissolves with rainwater to form sulphuric acid, known as acid rain
How is sulphuric acid formed? (1)
SO2 (g) + 0.5O2 (g) + H2O (l) –> H2SO4 (l)
How is nitric oxide produced? (1)
N2 (g) + O2 (g) –> 2NO (g)
How is nitrogen dioxide produced? (1)
2NO (g) + O2 (g) –> 2NO2 (g)
How is nitric acid produced? (1)
4NO2 (g) + 2H2O (l) + O2 (g) –> 4HNO3 (g)
How is sulphur dioxide gas removed from the atmosphere? (1)
Flue gas desulphurisation
How does desulphurisation work? (1)
Acidic sulphur dioxide gas is neutralised by an alkali
What is one method of desulphurisation? (1)
CaO(s) + 2H2O(l) + SO2(g) + 0.5 O2 –> CaSO4.2H2O(s)
What is the another method of desulphurisation? (1)
CaCO3(s) + 0.5 O2(g) + SO2(g) –> CaSO4(s) + CO2(g)
Removal of unburned hydrocarbons and nitrogen monoxide in catalytic converters (1)
C8H18 + 25NO –> 8CO2 + 9H2O + 12.5N2
What catalyst is used to remove the gas NO from exhaust gases in a car? (1)
Platinum/palladium/rhodium
What are catalytic converters made of and explain the advantage of having this structure (4)
Ceramic honeycomb coated with platinum, palladium and rhodium metals
Honeycomb structure:
Increases the surface area
Increases rate of reaction
Why is the production of carbon monoxide dangerous? (2)
Highly toxic and poisonous
Prevents haemoglobin in red blood cells from binding with oxygen
What does cracking involve? (1)
Breaking C-C bonds in alkanes
Why are C-C bonds broken in cracking and not C-H? (2)
C-C bonds are weaker than C-H bonds and so break more easily when heated
Why is UV light essential when combining an alkane with a halogen to form a haloalkane? (1)
Provides energy to break the halogen bond
What is a radical? (1)
A species with single unpaired electrons
How can the amount of further substitution be reduced? (1)
Use an excess of alkane which uses up all the halide radicals
What is a fuel? (1)
Something which releases heat energy when combusted
Environmental impact of nitrogen oxides (2)
Forms nitric acid which causes acid rain
Photochemical smog
Environmental impact of soot (carbon) (3)
Exacerbates asthma
Breathing problems
Damages lungs
Global dimming
Environmental impact of unburned hydrocarbons (1)
Photochemical smog
Environmental impact of carbon dioxide (3)
Greenhouse gas - global warming
Increases global temperatures
Speeds up climate change
Environmental impact of water vapour (3)
Greenhouse gas - global warming
Increases global temperatures
Speeds up climate change
What are flue gases (1)
Gases given out by power stations
What are greenhouse gases? (1)
Gases which trap infrared radiation, making the earth act like a greenhouse
What is the greenhouse effect and how does it contribute to global warming? (3)
Greenhouse gases trap infrared radiation in the atmosphere
Atmosphere heats up
Leading to global warming
What is meant by the term carbon-neutral in the context of this biofuel (1)
No net overall emissions of CO2 to atmosphere
