Alcohols and Haloalkanes Flashcards
What is the general formula of an alcohol?
Cn H2n+1 OH
What is the suffix of an alcohol with 2 hydroxyl (OH) groups?
-diol
What is a primary alcohol?
An alcohol where the -OH group is attached to a carbon with 1 alkyl group attached
What is a secondary alcohol?
An alcohol where the -OH group is attached to a carbon with 2 alkyl groups attached
What is a tertiary alcohol?
An alcohol where the -OH group is attached to a carbon with 3 alkyl groups attached
What is an alkyl group?
An alkane with a Hydrogen removed e.g CH3
What is electronegativity?
The ability of an atom to attract the bonding electrons in a covalent bond
Why are alcohols classed as polar molecules?
Because the electronegative hydroxyl groups pulls the electrons in the C-OH bond away from the carbon atom, forming a dipole
What dipoles are there in an O-H bond?
ẟ- O-H ẟ+
In an alcohol, what does the partial positive charge on the Hydrogen atom in the hydroxyl group cause?
It attracts the lone pairs on an oxygen from a neighbouring molecule, forming a Hydrogen bond
What happens, in terms of bonds, when you mix an alcohol with water?
Hydrogen bonds form between the -OH group and the H2O
What is the trend in solubility of alcohols as they increase in size?
As alcohols increase in size, they become less soluble in water
Why do alcohols become less soluble in water as they increase in size?
Smaller alcohols are more polar, meaning the Hydrogen bonding lets it mix freely with water. In larger alcohols, most of the molecule is a non-polar carbon chain, so there’s less attraction for the polar H2O molecules
Describe the volatility of alcohols
They have a low volatility
Why do alcohols have a low volatility?
Because they can form Hydrogen bonds (strongest type of intermolecular force) meaning it takes more energy to evaporate to a gas
What can be said about the boiling point of alcohols?
They have a relatively high boiling point
Why do alcohols have a relatively high boiling point?
Because they can form Hydrogen bonds (strongest type of intermolecular force) meaning it takes more energy to break the intermolecular bonds
What is the name of the reaction when an alcohol reacts with compounds containing Halide ions?
Substitution reaction
What does an alcohol turn into when undergoing a substitution reaction?
A Haloalkane, as the -OH group is replaced by the halide
What catalyst is used in an alcohol substitution reaction?
An acid catalyst, such as H2SO4 (sulfuric acid)
How do you make an alkene from an alcohol?
You can do an elimination reaction, which eliminates the water from the alcohol
What is a substitution reaction?
A reaction where some atoms from one reactant are swapped with atoms from another reactant
What is an elimination reaction?
A reaction in which a pair of atoms or group of atoms are removed from an organic compound
What 2 possible catalysts are used for the elimination reaction of alcohols?
Concentrated H2SO4 (sulfuric acid) Concentrated H3PO4 (phosphoric acid)
How do alcohols undergo an elimination reaction?
They are heated in the presence of a catalyst
What is the water molecule that is eliminated from an alcohol when making an alkene made up of?
A hydroxyl group and a hydrogen atom that was bonded to a carbon atom adjacent to the hydroxyl carbon
What are the products for the combustion of alcohols?
Water and carbon dioxide
What is the oxidising agent used for the oxidation of alcohols?
Acidified potassium dichromate (VI)
K2Cr2O7 / H2SO4
What are the 2 products, in chronological order of formation, for the oxidisation of primary alcohols?
Oxidised to aldehydes and then to carboxylic acid
What is the only product of the oxidation of secondary alcohols?
Ketones
What is the colour change for the oxidation of primary and secondary alcohols?
Orange —> Green
Why is the colour change for the oxidation of primary and secondary alcohols orange to green?
Because the orange dichromate ion is reduced to the green chromium ion, Cr 3+
What is the colour change for the oxidation of tertiary alcohols?
No colour change because tertiary alcohols don’t oxidise
What is the functional group of carbonyl compounds?
C=O
What is the general formula of aldehydes and ketones?
CnH2nO
What is the difference between aldehydes and ketones?
Aldehydes have a hydrogen and one alkyl group attached to the carbonyl carbon atom, whereas ketones have 2 alkyl groups, but no hydrogens, attached to the carbonyl carbon atom
What is the functional group of an aldehyde?
-CHO
What is the suffix for naming aldehydes?
-al (e.g. propanal)
Why don’t you have to name which carbon the functional group is on for aldehydes?
It’s always on carbon-1 atom
What is the suffix for naming ketones?
-one (e.g. propanone)
What is propanone commonly used for?
Nail varnish remover
What is the functional group of carboxylic acids?
-COOH
What is the suffix for naming carboxylic acids?
-oic (e.g. propanoic acid)
Why is the functional group of carboxylic acids not written as CO2H?
Written as COOH to show that the oxygens are different (one is part of carbonyl group and other is part of OH group)
What is a primary alcohol first oxidised into?
An aldehyde
What can an aldehyde, formed from the oxidation of a primary alcohol, be oxidised into?
A carboxylic acid
What is the notation used to represent an oxidising agent?
[O]
What conditions are needed to form an aldehyde from a primary alcohol?
Distillation
How do you form just the aldehyde from a primary alcohol?
By removing it from the oxidising agent as soon as it’s formed, otherwise it’ll oxidise further to form a carboxylic acid
Why do you use distillation apparatus to form an aldehyde from a primary alcohol?
Because it distils the aldehyde as soon as it forms, thus removing it from the oxidising agent
What does heating the primary alcohol using reflux mean for the products produced?
You still make an aldehyde first, but because it stays in the reaction vessel with the oxidising agent, it oxidises further to form a carboxylic acid
What is the balanced equation for the oxidation of a ethanol using distillation?
ethanol + [O] —> ethanal + water
What is the balanced equation for the oxidation of a ethanol using reflux?
ethanol + 2[O] —> ethanoic acid + water
What does heating under reflux mean?
Means you can increase the temperature of an organic reaction to boiling without losing volatile solvents, reactants or products
To form a carboxylic acid, what does a primary alcohol have to be heated under reflux with?
An excess amount of oxidising agent so that it is vigorously oxidised
How does heating under reflux mean that no volatile solvents, reactants or products are lost?
Because any vaporised compounds are cooled as they rise, so then condense and drip back into the reaction mixture
What does refluxing a secondary alcohol with an oxidising agent form?
A ketone
What is the balanced equation for the oxidation of propan-2-ol?
propan-2-ol + [O] —> propanone + water
Why is a ketone the only product of oxidising secondary alcohols?
Because ketones can’t be oxidised easily any further
How can you do a test to find out if an alcohol is tertiary or not?
If you heat the alcohol with acidified potassium dichromate, the solution will not change colour if it is a tertiary alcohol, because they can’t be oxidised. If it is a primary or secondary alcohol, the solution will turn green, as it can be oxidised
What is a haloalkane?
An alkane with at least one halogen replacing a hydrogen
If a haloalkane contains both bromine (bromo- suffix) and iodine (iodo- suffix), which do you write first when naming the haloalkane?
Bromo- because it’s before iodo- in the alphabet
Is the carbon-halogen bond in haloalkanes polar or non-polar?
Polar
Why is the carbon-halogen bond in haloalkanes polar?
Halogens are more electronegative than carbon, causing the electrons to be attracted to the halogen
Draw the dipoles of the carbon-halogen bond in haloalkanes
ẟ+ C-Br ẟ- (carbon has a positive charge because electrons shift towards the halogen)
What happens in a nucleophilic substitution reaction?
The lone pair of electrons on the nucleophile attacks a the slight positive charge on the carbon to create a new bond
What is the equation for the nucleophilic substitution of Halogen X?
RX + Nu- —> RNu + X-
where Nu is the nucleophile and R is the alkyl group
What is nucleophilic substitution?
Where a nucleophile attacks a polar molecule and replaces the functional group
What type of fission is the bond breaking between the carbon and the halogen in nucleophilic substitution?
Heterolytic - as both of the bonding electrons are taken by the halogen
What is a hydrolysis reaction?
A reaction where molecules are split up by water (which also split up into H+ and OH-)
What is the product of the hydrolysis of a haloalkane?
Alcohols
What are the 2 ways of doing hydrolysis of haloalkanes to make alcohols?
Hydrolysis with aqueous alkali
Hydrolysis with water
Give 2 examples of alkalis that could be used for the hydrolysis of haloalkanes?
Sodium hydroxide (NaOH) Potassium hydroxide (KOH)
What is the general equation for the hydrolysis of haloalkanes with aqueous alkali?
RX + -OH —> ROH + X-
Compare the speed of hydrolysis using water and using aqueous alkali
Using water is much slower because water is a weak nucelophile
What is the general equation for the hydrolysis of a haloalkane using water?
RX + H2O —> ROH + H+ X-
What happens with hydrolysis if you’ve got more than one halogen present in the molecule?
The halogen with the lowest bond enthalpy will be replaced first
How does the speed of when haloalkanes are hydrolysed depend on?
The bond enthalpy of the carbon-halogen bond
Which does faster hydrolysis, fluoroalkanes or iodoalkanes?
Iodoalkanes because the C-I bonds have a lower bond enthalpy than the C-F bonds
When doing the practical to compare hydrolysis rates of haloalkanes, why do you use water as the nucleophile instead of an alkali?
If you used the alkali the hydroxide ions would react with the silver nitrate to form a precipitate and mess up the results
What does CFC stand for?
Chlorofluorocarbons
Describe the stability of CFCs
Very stable because they contain no hydrogens
What are CFCs?
Fully halogenated paraffin hydrocarbons that contain only carbon, chlorine, and fluorine
Describe the volatility of CFCs
Volatile
Describe the flammability and toxicity of CFCs
Non-flammable and non-toxic
Where is the ozone layer?
A layer that is in a layer of the atmosphere called the stratosphere
What is the molecular formula for ozone?
O3
How does the ozone layer benefit humans?
It absorbs UV radiation from space, meaning it decreases the chance of sunburn or skin cancer
How does ozone form?
When an oxygen atom is broken down into 2 free radicals by UV radiation
What is the chemical mechanism for the formation of ozone?
O2 + UV —> O + O
O2 + O —> O3
How are holes forming in the ozone layer?
The CFCs that are travelling up into the atmosphere absorb UV radiation and split up into 2 chlorine radicals. These radicals then destroy ozone molecules and then are regenerated to destroy more ozone
Write the mechanism for the destruction of the ozone layer
CF2Cl2 + UV —> CF2Cl• + Cl•
Cl• + O3 —> O2 + ClO•
ClO• + O —> O2 + Cl•
On average, how many ozone molecules can a singular chlorine atom destroy before becoming stable?
10,000
What is the general equation for the destruction of ozone?
O3(g) + O(g) —> 2O2(g) … where Cl• is a catalyst
What type of catalyst is the Cl• in the destruction of ozone?
Homogenous catalyst, because it’s in the same phase (state) as the ozone molecules
What is the problem with CFCs being so stable?
They don’t get broken down in the lower atmosphere, so they can travel further up to the ozone layer where they destroy it
What is another example of free radicals that destroy the ozone layer, apart from Cl•?
NO• from nitrogen oxides
Gives 3 examples of where nitrogen oxides are produced from
Planes
Cars
Thunderstorms
How do thunderstorms release nitrogen oxides?
Each bolt of lightning carries electrical energy that is powerful enough to break the strong bonds of the nitrogen molecule in the atmosphere. Once split, the nitrogen atoms quickly bond to oxygen in the atmosphere, forming nitrogen dioxide
Why were CFCs banned?
Because scientific evidence showed that the advantages of using CFCs couldn’t outweigh the environmental damage they were causing
What was the Montreal Protocol 1987?
An international treaty to phase out the use of CFCs and other ozone-damaging haloalkanes by the year 2000
What does HCFCs stand for?
Hydrochlorofluorocarbons
What does HFCs stand for?
Hydrofluorocarbons
What 2 haloalkanes are being used instead of CFCs?
HCFCs
HFCs
Compare, on average, how long it takes CFCs to leave the atmosphere compared to HCFCs
CFCs take around 90 years whereas HCFCs take between 10-20 years
Do HCFCs damage the ozone layer?
Yes, but the effect is much less than CFCs
Do HFCs damage the ozone layer?
No because they don’t contain chlorine
What are HCFCs and HFCs examples of?
Greenhouse gases
What were CFCs originally used a lot in, until they were banned?
Fridges, Aerosols, Air-conditioning
What is the troposphere?
The lowest level of the atmosphere
What is the greenhouse effect?
The absorption and re-emission of infrared radiation by greenhouse gases in the troposphere
What happens when EM radiation reaches Earth?
It is absorbed then re-emitted as infrared radiation (heat)
What happens to the infrared radiation once the Earth has re-emitted it?
The gases in the troposphere absorbs it and then re-emits it in all direction, including back towards Earth
What are the 3 main greenhouse gases?
Methane
Carbon dioxide
Water vapour
What is a greenhouse gas?
A gas that absorbs and re-emits infrared radiation, thus contributing to the greenhouse effect
What happens to the bonds of the greenhouse gases when they absorb infrared radiation?
The bonds in the molecule vibrate more, this extra energy is passed on to other molecules in the air by collisions, giving them more kinetic energy and raising the temperature
What are the 3 factors that the contribution to the greenhouse effect depends on?
How much IR radiation one molecule of the gas absorbs
How much of that gas there is in the atmosphere
How long the gas stays in the atmosphere for
What is global warming?
The warming of the planet due to increased concentrations of greenhouse gases in the troposphere, which enhance the greenhouse effect
Why does the concentration of water vapour in the atmosphere stay roughly the same?
Because if there’s too much it falls to Earth as rain
What does anthropogenic mean?
Human impact on the environment
What are 3 environmental problems to do with global warming?
Ice caps will melt leading to a rise in sea levels
Stormier, less predictable weather
Less rainfall in some areas, leading to drought
What is the Kyoto Protocol of 1997?
Where industrialised countries, such as UK, promised to reduce greenhouse gas emissions to agreed levels
When did the Kyoto Protocol come to an end?
2012
How are governments working to reduce the amount of greenhouse gases going into the atmosphere?
Using more renewable energy resources, such as wind turbines and solar farms
