Topic 9 - Hydrocarbons, Alcohols, Carboxylic Acids, Polymers Flashcards
hydrocarbons
molecular compounds that contain only carbon and hydrogen
alkanes general formula
CnH2n+2
When are molecules saturated
When all the carbon-carbon covalent bonds are single bonds
When are molecules unsaturated?
When they contain at least one double covalent bond between adjacent carbon atoms
alkenes general formula
CnH2n
What bonds do alkenes have?
carbon-carbon double bond
isomers
Molecules with the same molecular formula, the different arrangements of atoms
What do numbers in isomers show?
The position of the double bond
What is formed in the complete combustion of a hydrocarbon?
Only carbon dioxide and water is formed when there is a plentiful supply of oxygen
What gets produced in incomplete combustion?
If there is an insufficient amount of oxygen, full oxidisation does not occur and carbon (soot) and carbon monoxide can be formed as well as water and carbon dioxide
When and how is the bromine water test used?
To tell the difference between alkenes and alkenes because ALKANES do not react with it (cause decolourisation)
what and why is the colour change in the bromine water test if an alkene is detected
the orange-brown colour turns colourless because the C=C double bond reacts with the bromine to form a colourless product, bromine is therefore removed from the solution which looses it colour (hence why it doesn’t work with alkenes because they don’t have a double bond)
addition reaction
Reaction in which reactants combined to form one larger product molecule and no other products
fermentation
Plant material containing sugars is mixed with water and yeast -> enzymes in the yeast, turn the sugars into ethanol and carbon dioxide
What do the percentages mean in alcohols
How much ethanol they have
How is ethanol made?
Through fermentation (sugars)
Why is an airlock in the neck of a jar when making ethanol necessary (fermentation)?
Allow carbon dioxide to escape while keeping air out; this is necessary because yeast fermentation is a type of anaerobic respiration and only occurs in the absence of oxygen
What is fractional distillation of an ethanol solution needed if the concentrations are higher than 15%?
Cause higher concentrations kill the yeast cell
How is a fractional distillation column used for ethanol % above 15?
- Ethanol boiling point (78°C) is lower than the boiling point of water (100°C)
- The heated liquids evaporate and their vapour cool as they rise up the fractionating column
- Cause the ethanol has a lower boiling point it remains a gas for longer and separates from the water -> as a result the first fraction that is collected contains a higher percentage of ethanol
What do alkanes end in
-ane
what do alkenes end in
-ene
what do alcohols end in
-anol
alcohol general formula
CnH2n+1OH
Chemical properties of alcohols
- Produces carbon dioxide and water on complete combustion
- Can be oxidised to form compounds called carboxylic acid
- Reacts with reactive metals, forming hydrogen gas is one of the products
Functional group
The atom of group of atoms in a molecule that is responsible for its main chemical reactions
Why do alcohols have similar chemical properties?
Because they all contain one -OH functional group
What are the uses of alcohol?
- solvents for cosmetics, medical drugs, varnishes
- Methanol and ethanol a widely used fuels and can be made from renewable sources
What is the method for the combustion of alcohols (CORE PRACTICAL)
- Measure the mass of an alcohol burner and cap; record the mass and the name of the alcohol
- Place the alcohol burner in the centre of a heat resistant mat
- Using the measuring cylinder to add 100 cm³ of cold water to a conical flask
- Measure and record the initial temperature of the water and clamp the flask above the alcohol burner
- light the wick of the burner and allow the water to heat up by about 40°C
- Replace the cap on the burner and measure and record the final temperature of the water
- Measure the mass of the alcohol burner and cap again and record the mass
- Calculate the mass of the alcohol burned to produce a 1°C rise in temperature
- repeat all steps using fresh cold water and a different alcohol
carboxylic acid general formula
CnH2n+1COOH
How are carboxylic acids usually formed?
By the gentle oxidisation of alcohols using oxidising agents such as hot copper oxide
What are the chemical properties of carboxylic acids?
- form solutions with a pH less than 7 (if soluable)
- React with metals to form a salt and hydrogen
- React with bases to form salt and water
- react with carbonates to form a salt, water and carbon dioxide
-> acidic properties due to the presence of -COOH functional group
polymer
large molecule made from lots of small molecules
polymerisation
process in which monomers join together
addition polymerisation (alkenes)
process in which monomers are together in this way:
- e.g. ethene molecules have a double covalent bond between the carbon atoms; one of the bonds in the double born right safe and another evening molecule add on
-> this process happens again and again forming a long chain
How would you show a repeating unit?
what do equations for polymerisation show
The structural formula of the monomer and the repeating unit
General equation of additional polymerisation in alkenes
synthetic polymer
A polymer manufactured in a laboratory or factory using chemical reactions
naturally occurring polymer examples
protein, starch, DNA
examples of synthetic polymers
polythene, polyester, nylon
properties and uses of poly(ethene) (common name: polythene)
properties: flexible, cheap, good insulator
uses: plastic bags, plastic bottles, clingfilm
Properties and uses of poly(propene) (common name: polypropylene)
properties: flexible, doesn’t shatter
uses: buckets, bowls, crates, ropes, carpets
Properties and uses of poly(chloroethene) (common name: polyvinyl chloride, PVC)
Properties: tough, good insulator, can be made hard or flexible
Uses: window frames, gutters, pipes, installation for electrical wires
Properties and uses of poly(tetrafluororthene) (common name: PTFE, Teflon)
Properties: tough, slippery
Uses: nonstick coatings for frying pan and kitchen utensils, burette taps, stain proofing clothing and carpets
condensation polymerisation
monomers join together and eliminate a small molecule such as water
Ester functional group
-COO-
when are esters formed
When carboxylic acids react with an alcohol in the presence of a catalyst
-> this is a condensation reaction because of water is also produced
ester word equation
carboxylic acid + alcohol -> ester + water
polyester
A long chain molecule that contains many ester links
how is water made in an ester equation
polyester general formula
what are problems with polymers
- most of the monomers used to make synthetic polymers are obtained from crude oil and crude is an finite resource and is non-renewable so chemists will need to find new sources of monomers in the future
- synthetic polymers are not biodegradable (breakdown naturally into smaller components through the action of microorganisms) so they last for a long time however this also means they do not rot when they’re thrown away
ways of disposing plastsics
- incineration and the energy released can be used to generate electricity however all plastics produce carbon dioxide and some plastics produce toxic substances when they burn
- recycling (reprosessing plastic into new materials)
- landfilling (burying plastic in a landfill)
Steps needed to obtain a new item after recycling
- collect the waste
- Sort the waste into different type types of polymer - this is often done by hand which is time-consuming and expensive
- Dispose of wastes that cannot be recycled in landfill sites.
- Clean the polymers and grind them into chippings.
- Purify the chippings.
- Melt the chippings then process them into a new product.
Clothes and symbols used on plastic items to show what they made of
