Organic Chemistry A1 Flashcards
Addition Polymers, Ozone, Haloalkanes, Nucleophilic substitution, Alcohols… Module 4
What are polymers?
Large molecules made up of small repeating units.
What is addition polymerisation?
When alkenes react together by breaking open their double bonds forming a long chain.
How are polymers disposed of? What are the strengths and limitations of these?
LANDFILL
+ Cheap and easy
- Not biodegradable
COMBUSTION FOR ENERGY
+ Releases energy
- Makes CO2
- Makes dangerous gases
RECYCLING
+ Less material goes to landfill
+ Conserves finite fossil fuels
- Must be sorted and collected
- Some plastics are hard to recycle
FEEDSTOCK RECYCLING
+ Can handle unsorted and unwashed polymers
+ Can be used as raw material to make a new polymer
- Requires a high amount of energy
Name 2 new polymers and describe them
BIOPLASTICS are produced from plants.
+ Renewable, sustainable, biodegradable, do not contains halogens so don’t produce toxic gases.
PHOTODEGRADABLE POLYMERS are weakened by light and then start to break down.
How can HCl gas from burning PVC be removed from waste mixture?
Neutralise with a base - e.g. NaCO3
Identify a hazard of burning PVC - poly(chloroethene)
It releases toxic HCl gas
The Ozone layer is found in the __________. It is continually being formed and broken down by __ _________.
The ozone layer is very important to life on earth because it absorbs ___ radiation (which can cause sunburns and ___ ______) from the sun.
Stratosphere
UV radiation
UV-B
Skin Cancer
What are the uses of chlorofluorocarbons?
- Refrigerants
- Air-conditioning
- Aerosol propellants
- Solvents
What are the properties of chlorofluorocarbons?
- Volatile (have low b.p’s)
- stable/non-flammable
- non-toxic
What are the problems with chlorofluorocarbons?
Long-lasting and catalyse the breakdown of the ozone layer.
How do CFCs break down the ozone’s layer?
INITIATION
- A C-Cl bond breaks, forming a Cl radical.
CF2Cl2 —> .CF2Cl + .Cl
- This is triggered by UV light and takes place in the stratosphere.
- The C-Cl bond breaks as it has a lower bond enthalpy than C-F.
PROPAGATION
- The Cl radical reacts with O3
.Cl + O3 —> .ClO + O2
.ClO + O —> .Cl + O2
Overall Equation:
O3 + O —> 2O2
What other radicals (other than CFCs) also catalyse the breakdown of the ozone layer and are produced in lightening strikes and jet engines? What are the propagation equations for this reaction?
.NO radicals (produced by O2 and N2)
.NO + O3 —> .NO2 + O2
.NO2 + O —> .NO + O2
O3 + O —> 2O2
What are Haloalkanes?
A homologous series of organic compounds that contain a halogen.
How are haloalkanes classified?
By the number of alkyl groups bonded directly to the halogen-bearing carbon.
(Primary = 0 or 1, Secondary = 2, Tertiary = 3)
What do hydrolysis reactions involve? What type of reaction is it when haloalkanes are involved? What Is formed through this reaction?
The splitting of molecules with water to form new molecules.
It is a substitution reaction where a halogen is replaced by a hydroxyl group.
R-X + H2O —> R-OH + H+ + X-
Alcohols are formed.
What does the rate of hydrolysis depend on?
The strength of the carbon-halogen bond.
E.g. C-F bonds are strongest and C-I are weakest. Therefore the trend in rate is iodoalkanes > bromoalkanes > chloroalkanes
Fluoroalkanes are unreactive as the C-F bond is so strong.
What experiment can you do to investigate the differences in rates of reactions between haloalkanes?
Hydrolysis reactions of iodo, bromo and chloroalkanes in aqueous silver nitrate and ethanol. (Ethanol is added to help mix the water and haloalkane together).
As the reaction takes place halogen ions are produced which then make AgX precipitates.
How can haloalkanes be converted to alcohols?
Using aqueous NaOH and heated under reflux.
What is a nucleophile?
An electron pair donor (often delta negative)
What happens in nucleophilic substitution? What is the name of the delta positive carbon centre?
Due to differences in electronegativity, carbon-halogen bonds are polar.
As electrons in the C-X bond are attracted to the halogen, this leaves the carbon with a positive dipole. The carbon is referred to as an electron-deficient centre.
How are alcohols classified?
Primary, secondary or tertiary depending on the number of carbons attached to the carbon bonded to the -OH group
What kind of intermolecular forces do alcohols have?
London forces and hydrogen bonds due to the -OH group
Are Alcohols more or less soluble in water than alkanes? Why?
Alcohols are mole soluble in water than alkanes as alcohols are able to undergo hydrogen-bonding with water molecules.
Do alcohols have higher or lower b.p’s than alkanes?
Alcohols have higher b.p’s than alkanes as they have hydrogen bonding as well as London forces while alkanes only have London forces.
What is an elimination reaction?
The removal of a small molecule from a larger one. One reactant can form two products.
What is dehydration? What are the conditions?
When alcohols lose water in an elimination reaction to form alkenes.
Conditions: H3PO4 / H2SO4 catalyst and heating by reflux
What happens at a molecular level in dehydration of alcohols?
The OH group along with an adjacent H is lost, to form a water molecule. A double bond forms between the two carbons.
Alcohols react with ______ ______ to form haloalkanes.
What are the conditions?
Hydrogen/Na halides
Conditions: Heat under reflux with H2SO4
Alcohols always undergo ________ combustion.
Complete
Acidified potassium dichromate changes colour from _____ to _____ when mixed with a primary or secondary alcohol.
Orange to green
Primary alcohols can be oxidised to either _______ or ______ _____ depending on the conditions.
Secondary alcohols can be oxidised to _______.
Tertiary alcohols ______ be oxidised.
Aldehydes
Carboxylic acids
Ketones
Cannot
What are the conditions needed to form an aldehyde from an alcohol? What does the aldehyde functional group look like?
Conditions: distil a primary alcohol with K2Cr2O7 and H2SO4
A carbon singly bonded to an H and doubly bonded to an O.
What are the conditions needed to form an carboxylic acid from an alcohol? What does the carboxylic acid functional group look like?
Conditions: reflux a primary alcohol with K2Cr2O7 and H2SO4
A carbon doubly bonded to an O and singly bonded to an OH group.
Excess oxidising agent is used to make _______ ______. ( 2[O] )
Carboxylic acid
What are the conditions needed to form ketones from an alcohol? What does the ketone functional group look like?
Conditions: reflux a secondary alcohol with K2Cr2O7 and H2SO4
A carbon doubly bonded to an Oxygen
Why does the C-Cl bond break instead of the C-F bond in CFCs when reacting with ozone?
Because it has a lower bond enthalpy (strength) than C-F.
