SC22/23/24: Hydrocarbons, Carboxylic Acids & Polymers Flashcards
SC22a Alkanes & Alkenes
A) Describe what is ment by a homologous series
B) State the first 6 members of the alkane homologus series
A) A series of molecules that have general formula & vary in a single feature ( such as carbon chain length ) form an homologus series.
B) Members include;
- Methane -> CH4
- Ethane -> C2H6
- Propane -> C3H8
- Butane -> C4H10
- Pentane -> C5H12
- Hexane -> C6H14
SC22a Alkanes & Alkenes
A) Describe what is ment by a functional group ( in relavence to Alkenes )
B) State the first 3 members in the series
C) State what an Isomer is
A) Alkenes are a homologus series of unsaturated hydrocarbons with the general formula CnH2n
- The Carbon-Carbon double bond is known as a functional group. This is an atom or group of atoms that is manly responsible for a molecules chemical properties.
B) Members include;
- Ethene -> C2H4
- Propene -> C3H6
- Butene -> C4H8
C) Molecules with the same molecular formula but different arrangement of atoms are called isomers.
- Butene has 2 isomers, but-1-ene and but-2-ene.
SC22b Reactions of alkanes and alkenes
A) Describe the bromine water test
B) Describe what is ment by Addition reactions
A) Bromine water has an orange-brown colour. When it is mixed with alkenes a chemical reaction occurs, leading to colourless products.
- Alkanes don’t cause decolourisation & so bromine water is used to test between the 2.
- This test works since the alkene is unsaturated so the double Carbon bond reacts with the bromine, removing it from the solution.
B) A reaction in which reactants combine to form one larger product molecule & no other products is called an addition reaction.
SC23a Ethanol production
Describe how alcholic drinks are produced prior to fermentation.
- Ethanol in alcoholic drinks is made from sugars. Sugars are small, soluble substances that belong to a group called carbohydrates. Many fruits contain alot of sugars.
- Seeds contain a carbohydrate called starch, which is a long polymer. Starch must be broken down into sugars in order to make alcoholic drinks.
- Seeds are germinated before using them to make ethanol because, during this process, enzymes in the seeds naturally turn starch into sugars.
SC23a Ethanol production
Describe the role of fermentation in ethanol production
- Plant materials containing sugars is mixed with water and yeast. Enzymes in the yeast turn the sugars into ethanol & CO2, in a process called fermentation.
- glucose -> ethanol + carbon dioxide.
- During fermentation, temperature & pH are controlled to ensure the enzymes work at their best. An air lock allows CO2 to escape while keeping air out. This is needed because fermentation is a type of anaerobic respiration.
- The fermentation process only produces concentration up to 15% as higher conc would kill the yeast cells. More concentrated ethanol solution are formed by fractional distillation.
SC23b Alcohols
A) State the first 4 members of the alcohol homologus series.
B) Describe the similar chemical properties alcohols have.
A) Members include; ( Formula -> CnH2n+1OH )
- Methanol -> CH3OH
- Ethanol -> C2H5OH
- Propanol -> C3H7OH
- Butanol -> C4H9OH
B) All alcohols have similar chemical properties, they all;
- produce carbon dioxide and water on complete combustion.
- can be oxidised to form compounds called carboxylic acids.
- react with reactive metals, such as sodium, forming hydrogen gas as one of the products. -> reactivity depends on carbon chain length.
SC23b Alcohols
A) Describe the functional group for alcohols
B) Describe some uses for alcohols
A) Alcohols have similar properties because they all contain one - OH functional group.
- Alcohols can be dehydrated to form alkenes.
B) Many alcohols are used as solvents for cosmetics, medical drugs and varnishes. Methanol & ethanol are widely used as fuels & can be made from renewable sources.
- Scientists are now working on developing processes to make propanol and butanol fuels from renewable sources, such as fermenting plant cellulose using bacteria.
SC23b Core practical - The combustion of alcohols
Describe how you could investigate the energy giving out by different alcohols
Aim - To investigate the temperature change of water by combustion
- A: Measure the mass of an alcohol burner and cap. Record the mass & the name of the alcohol.
- B: Place the alcohol burner in the centre of a heat-resistance mat.
- C: Use a measuring cynlinder to add 100cm^3 of cold water to a conical flask.
- D: Measure & record the initial temp of water and clamp the flask above the alcohol burner.
- E: Light the wick of the burner and allow the water to heat up by about 40C
- F: Replace the cap on the burner & measure & record the final temp of the water.
- G: Measure & record the mass of the alcohol burner & cap.
- H: Calculate the mass of the alcohol burned to produce 1C rise of temp.
- I: Repeat steps A -> H using fresh water, cold water & a new alcohol.
SC23c Carboxylic acids
A) Describe how ethanoic acid is formed
B) State the first 4 members of the Carboxylic acid series.
A) This occurs in the reaction: Oxygen + Ethanol -> Ethaonic acid + Water
- An oxygen molecule collides with the functional group of an ethanol molecule, & 2 hydrogen atoms are removed.
- The carbon atom that lost the hydrogens form a double bond with an oxygen molecule.
- The hydrogen molecules from the ethanol combine with an oxygen molecule to form water.
B) Members include; ( Formula -> CnH2n+1COOH )
- Methanoic acid -> HCOOH
- Ethanoic acid -> CH3COOH
- Propanoic acid -> C2H5COOH
- Butanoic acid -> C3H7COOH
SC23c Carboxylic acids
Describe the properties of carboxylic acids.
The carboxylic acids have similar chemical properties. They all;
- form solutions with a pH less than 7 ( if soluble )
- react with metals to form a salt & hydrogen
- react with bases to form a salt and water
- react with carbonates to form a salt, water & CO2.
The acidic properties are due to the presence of the -COOH functional group. In solution this group forms an hydrogen ion, while the rest of the molecule forms the negative ion that makes the salt.
SC24a Addition polymerisation
A) Describe what a polymer is
B) Describe how poly(ethene) is formed.
A) A polymer is a large molecule made from lots of small molecules, called monomers. The process in which monomers join together is called polymerisation.
- A polymer has a high average relative molecular mass.
B) Poly(ethene) is formed by the joining of ethene monomers. Ethene molecules have double covalent bonds that break open allowing another ethene molecule to be added on.
SC24a Addition polymerisation
Describe some naturally occuring polymers
- DNA is made from 4 different monomers called nucleotides.
- Starch is a polymer made from a sugar called glucose.
- Protiens are polymers made from amino acids.
SC24b Polymer properties and uses
Describe the properties and uses of;
A) Poly(ethene)
B) Poly(propene)
C) Poly(chloroethene)
D) Poly(tetrafluoroethene)
A) Poly(ethene)
- Properties; flexible, cheap, good insulator
- Uses; plastic bag, plastic bottles, cling film, polytunnels
B) Poly(propene)
- Properties; flexible, does not shatter
- Uses; buckets and bowls, crates, ropes, carpets
C) Poly(chloroethene)
- Properties; tought, good insulator, can be made hard or flexible
- Uses; window frames, gutters, pipes, insulation for electrical wires.
D) Poly(tetrafluoroethene) - PTFE
- Properties; tough, slippery
- Uses; non-stick coatings for frying pans and kitchen utensils, burette taps, stain-proofing clothing & carpets.
SC24c Condensation polymerisation
Explain what is ment by condensation polymerisation ( linking to polyesters )
- Polyesters are synthetic made by condensation polymerisation in which monomers join together and eliminate a small molecule, such as water.
- Esters are organic compounds that contain the functional group -COO- ( Double bond between carbon & 1 oxygen atom )
- Esters are formed when a carboxylic acid reacts with an alcohol, in the presence of a catalyst. carboxylic acid + alcohol -> ester + water.
- The monomers that form a polyester contain alcohol & carboxylic acid functional groups. To form a long chain, each monomer must have 2 functional groups, 1 at each end of the monomer.
SC24d Problems with polymers
Describe some problems that are associated with polymers.
- Most of the monomers needed to make synthetic polymers are obtained from crude oils, which is a finite resource and is non-renewable, so chemists we need to find a new source for monomers in the future.
- Most synthetic polymers are useful because they are not biodegradable & so they last for a long time. However, this also means that they do not rot when they are throw away.
- In landsites, the non-biodegradable polymers will last for many years. Some waste is incinerated and energy released is used for electricity, however, all plastic produce CO2 when burnt which is a green house gas.
SC24d Problems with polymers
Describe the process of recycling polymers
It is difficult to recycle polymers because many steps are needed. Main steps are outlines below.
- i: Collect the waste - this may involve kerbside collection or people taking it to a collection point.
- ii: Sort the waste into different types of polymer - this is often done by hand which is time-consuming and expensive.
- iii: Dispose of the waste that cannot be recycled in a landfill site.
- iv: Clean the polymers & grind them into chippings
- v: Purify the chippings
- vi: Melt the chippings then process them into new product.
