C6.2 Flashcards
What are hydrocarbons?
- compounds made from hydrogen and carbon only
What are alkanes?
- alkanes are a homologous series of hydrocarbons (contain only C and Hydrogen atoms)
- same general formula and are saturated hydrocarbons
- only have single bonds between the atoms (form covalent bonds)
What is a homologous group of chemicals?
- chemicals with similar chemical structures
What are saturated hydrocarbons means?
- carbon can make 4 bonds and H can make 1 so saturated means all atoms have formed bonds with as many other atoms as they can
- only have single bonds
How are Alkane names made?
- first part = no. of C atoms present
- ending = -ane
What are the names for alkanes with 1-6 no. of carbons?
1 = methane - (CH4 = chemical formula) 2 = ethane - C2H6 3 = propane - C3H8 4 = butane - C4H10 5 = pentane - C5H12 6 = hexane - C6H14
What is the general formula for alkanes?
CnH2n+2
E.g.
Propane
= C3 and H(3x2)+2 = C3H8
How do you draw the displayed formula model for alkanes?
- place n of carbons in the middle and attach them with single bonds (1 line)
- place H atoms around the outside making sure C are bonded to 4 in total and H is bonded to 1
E.g. butane = H H H H
I I I I
H- C-C-C-C - H
I I I I
H H H H
What reactions do alkanes and other hydrocarbons take part in?
- combustion
- complete = hydrocarbon burns in O2 to form CO2 and H2O = complete oxidation of hydrocarbon into CO2 and H2O
- incomplete = hydrocarbon burns in limited supply of O2 to form CO (carbon monoxide- poisonous to humans), water and carbon in the form of soot
- both types can occur at the same time = mixture of combustion products
What are alkenes?
- homologous series of hydrocarbons
- unsaturated as they contain at least 1 double bond (they can make more bonds as the double bond can open up, allowing the two C to bond with other atoms)
What is the general formula for alkenes?
Cn+H2n
e.g. Propene so 3 carbons
so C3H6
What are the first 4 alkenes?
Ethene = C2H4 Propene = C3H6 Butene= C4H8 Pentene = C5H10
How do you draw the displayed formula model for an alkene?
- find out the number of Carbon atoms
- Place in the middle and put 1 double bond between the carbons
- Add Hydrogen atoms around outside making sure Carbon bond to 4 (a double on dis 2) and Hydrogen is 1
What reactions can alkenes go through?
- undergoes combustion with the same products as alkanes
- complete = HC (hydrocarbon) + 02 –> C02+H2O
- incomplete = HC +O2 –> C+ CO + H2O
What is the functional group of alkenes?
C=C
What are functional groups?
atoms/ group of atoms or types of bonds in a molecule that is responsible for the characteristic reaction of the substance
(the type of reaction depends on that bond)
What are addition reactions?
- where atoms/groups of atoms combine with a molecule to form a larger molecule with no other product (e.g. addition polymers)
How can you test for alkenes?
- when added to bromine water, it will decolourise the bromine water = turning it from orange to colourless (shake it)
- this is as the double bond can open up and form bonds with the bromine
e.g. ethene:
start off with ethene and add bromine = dibromine
C2H4 + Br2 –> C2H4Br2
Why does the alkene test work with bromine water?
Alkanes don’t have double bonds and therefore don’t react with the bromine water
What is hydrogenation?
- alkene reacts with hydrogen in the presence of a nickel catalyst in a process called hydrogenation
- the hydrogen reacts with the double-bonded carbons and adds across the double bond = forming an alkane
What is the functional group of alcohols and what do they end in?
- form a homologous series
- contain hydroxyl functional group OH- (can have more than one)
- names end in -ol
What is the general formula for alcohols?
- CnH2n+1OH
E.g. ethanol has 2 carbons
So C2H5OH
- to display it, put both C is the middle and attach O-H to the right
H H
I I
H—C — C—O—H
I I
H HHow do you write alcohol names?
- basic naming for Alkanes but replace -e with -ol
- always write OH at the end
What reactions are alcohol involved in?
- complete combustion - burn in O2 to produce CO2 + H2O
- incomplete combustion - produce water vapour, C and CO
- oxidised to for carboxylic acids
How is alcohol is oxidised?
- gains oxygen and loses e-
- forms carboxylic acids (need an oxidising agent - postassium manganate (VII) )
- reaction change from purple to colourless (manganese (VII) is reduced to manganese (II) ions)
- oxidation only happens if -OH is joined to a carbon which is only attached to 1 carbon itself
What is the oxidisation of ethanol?
Ethanol + potassium manganate (VII) —> Ethanoic acid
What is the functional group of carboxylic acids and how do you name them?
- -COOH (carboxylic group)
- same as alkanes but ends in -anoic acid
What is the general formula for carboxylic acids?
- Cn-1H2n-1COOH (1 carbon is already in functional group)
- e.g. Pentatonic acid = C4H9COOH
What type of acids are carboxylic acids and how do they react with metal, alkali/base and carbonates?
- weak acids
- React with metal = salt and hydrogen
- React with alkali/base = salt and water
- React with carbonate = salt and water and carbon dioxide
What endings do salts have?
- oate
- ethanoic acid + sodium carbonate —> sodium ethanoate + water + carbon dioxide
2CH3COOH (aq) + Na2CO3 (aq) —> CH3COONa (aq) + H2O (l) + CO2 (g)
What are the first 4 carboxylic acids?
- methanoic acid = HCOOH
- ethanoic acid = CH3COOH
- propanoic acid = C2H5COOH
- butanoic acid = C3H7COOH
How is crude oil formed?
- from the buried remains of marine plants, animals (fossil fuels)and over millions of years with high temp and pa it turns into crude oil which can be drilled up
- found in rocks
What are 2 other fossil fuels except crude oil?
- coal and natural gas
- finite does limited amount and used up faster than being made
What is crude oil our main source for?
- of hydrocarbons
- used in raw material or feed stock to create lots of petrochemicals (petrol/natural gas)
How are crude oil compounds separated?
- fractional distillation
- oil is heated until most of it has turned into has
- gases enter fractionating column and liquid bitumen is drained off the bottom
- there’s a temp gradient in the column (hot = 350C and top= 25C)
- longer hydrocarbons have high b.p. so they turn back into liquid and drain out of the column early on when they’re near the bottom and shorter hydrocarbons have lower b.p so turn to liquid much later near the top of column
What is the crude oil separated into?
- diff fractions
- each fraction has a mixture of hydrocarbons - mainly alkanes with similar b.p
Name the fractions of crude oil, from the top to the bottom
- LPG = liquefied petroleum gas (has propane & butane) at top - 3Hc
- petrol - 8Hc
- (Naphtha (used as raw material in industrial processes)) - 10Hc
- Paraffin (kerosine) - 15Hc
- diesel - 20Hc
- heating oil - 35 Hc
- fuel oil (or lubricating oil) - 40Hc
- (crude oil goes in)
- bitumen liquid at bottom - 70Hc
What are the 2 types of bonds in crude oil?
- has 2 types of bonds
- strong covalent bonds between atoms within each hydrocarbon (Hc) molecule
- intermolecular forces between diff hydrocarbon molecules in mixture
Why does crude oil separate?
- heated = molecules are supplied with extra energy so move about and eventually enough energy to overcome imf that keep it with other molecules = becomes a gas
- cov bonds are stronger than imf so don’t break = this is why you don’t get lots of little molecules (hydrocarbon chain doesn’t break)
Why do big molecules have higher b.p than smaller molecules?
- imf break easily in small molecules as there are much stronger between big molecules
- if a big molecule can overcome the forces attracting it to another molecule at one point = more places that are strong enough to hold it in place
How are the fuels provided by crude oil important?
- provides the energy to generate electricity, heat homes etc.
- oil = fuel for transport (cars, trains, planes) and provides raw materials to make chemicals like plastic
- population increases = countries likes India and China = more developed so more fossil fuels burnt for electricity (increase home use and manufacture industries)
Why should we start thinking about other types of power and not crude oil?
- non - renewable
- new reserves are sometimes found and new tech means we can get to oil that used to be diff to extract but one day we will run out
- alternative energy sources = nuclear/wind power for electricity, ethanol to power cars, solar energy to heat water
- some think = stop using oil for fuels and keep it for plastic/chemicals= conflict for resources between fuel and chemical industries
What is cracking?
- converting large alkane molecules into smaller and more useful hydrocarbons (alkanes/alkenes)
- form of thermal decomposition (breakdown due to heat)
- breaks the strong cov bonds (need lots of energy)
- also produces alkene molecules which can be used to make polymers (mostly plastics)
What are longer molecules cracked?
- more demand for petrol and diesel than the supply
- but more supply than demand fro paraffin, heating/fuel oil and bitumen
What is the process of cracking?
- vaporised hydrocarbons are passed over powdered catalyst (silica/alumina) at about 600 - 700C and 70atm
- aluminium oxide is used as a catalyst
- long chain molecules split apart/crack on the surface of the bits of the catalyst
What happens when you crack liquid paraffin?
It changes to octane (petrol) and ethene (plastics)
- also other products depending on what’s in the paraffin
Why can’t we use fractional distillation on long chain alkanes and use that for our fuel?
- as long chain alkanes don’t flow easily and are hard to ignite
- we make too much of the fractions with large molecules at high b.p. to be sold
- and inadequate amounts of small molecule fractions with low b.p in high demand
What are the products of cracking?
- 90% of crude oil is used in petrol, diesel and rest is used in chemical industries to make polymers
- alkene molecules for polymers like plastic
What are addition polymers made of?
- jointing lots of small molecules called monomers
- monomers making up addition polymers have a double covalent bond
- molecules with atleast 1 double cov bond between carbon atoms are called unsaturated
- molecules with single bonds only are saturated
What reaction do addition polymers undergo?
- addition reaction
- do this as monomers are alkenes so have a double carbon bond which can break/open up and join new carbons to form new polymer chains
How do you name the polymer?
- polymer name = poly(monomer)
E.g ethene = poly(ethene)=polyethene
However chloroethene = poly(chloroethene)= but common name is PVC (polyvinyl)
What is the general formula of a polymer?
(Monomer formulae)n
How do you draw the displayed formula model for monomers and polymers?
Monomers to polymers=
- join carbons in a row with no double bonds
- but brackets around it and put n on the right (n number of monomers)
- draw a line from both carbons to show the chain continues
Polymers to monomers =
- take out brackets, n and bonds at the end on carbons
- add the double bond between the carbon and draw out the middle
How can you make addition polymers in the lab?
- hard as alkenes don’t polymerise by the self
- need to add a chemical initiator
- after adding initiator to alkene monomers, heat the reaction mixture
- as it includes flammable chemicals, use water bath rather than Bunsen
What are the conditions needed for addition polymers?
- high pressure
- catalyst
How can you make polystyrene?
- often used as packaging
- heat phenylalanine (monomer) in water bath with the initiator (in this case, a chemical called di(dodecanoyl)
Give examples of 3 naturally occurring polymers:
- DNA
- Proteins
- Carbohydrates
Describe DNA in terms of its structure
- complex molecules that contains genetic information
- polymer made of monomers called nucleotides that bond together in a polymerisation reaction
- 4 diff. nucleotide monomers, A-C and G-T that for, hydrogen bonds between them to hold the double helix shape together
Describe proteins in terms of its structure
- polymers are made from monomers called Amino acids through condensation polymerisation
- there are 20 diff amino acids that occur naturally in our body and each amino acid has a reactive functional group at the end that joins them end to end and all proteins are diff combinations of them (e.g enzymes)
- they are polyamides
Describe carbohydrates in terms of its structure
- molecules containing carbon, hydrogen and oxygen and are used by living things to produce energy
- they are made from the monomers simple sugars with join into complex carbs (glucose joins to make starch)
- Starch and cellulose are large complex carbs which are made up of many small units of carbs (known as sugars) in a long chain
What is condensation polymerisation?
- 2 molecules react together to form one large molecule and one smaller molecule (normally water)
- involves 2 diff types of monomers and each monomers needs to have at least 2 functional groups ( one at each end of monomer)
- each functional group can’t react with another monomer’s function groups creating long chains of alternating monomers and with each new bond that forms, a small molecules (water ) is lost
What happens when a carboxylic acid alcohol react?
Forms an organic compound called an ester and water
E.g ethanoic acid + ethanol —> ethyl ethanoate + water
What conditions do condensation polymers need?
- don’t need catalyst and occur at room temp and Pa
- monomers need 2 functional groups (e.g proteins)
What functional groups do amino acids have?
2 = Amino and carboxylic
- amino group = NH2
- carboxylic group = COOH
- monomers (2 amino acids) are joined by 2 functional group to form an amide group (CONH)
How are polyesters formed?
- polyester = artificial condensation polymer
- made from carboxylic acid with 2 carboxylic groups (dicarboxylic acid) and alcohol with 2 hydroxyl groups (diol)
- forms many ester groups when formed (water is eliminated)
- used for clothing, fizzy drink bottles (PET)
How are polyamides formed?
- polyamide = artificial condensation polymer
- polyamide = carboxylic acid with 2 carboxylic groups and amine monomers with 2 amino groups (diamine)
- forms many amide groups (water is eliminated)
- e.g is nylon which is used for clothes and carpets
Give an example of a condensation polymer that can be made in the lab:
Nylon-6,6 is a condensation polymer that can be made in the lab
How can nylon-6,6 be made in the lab?
- mix 1,6-diaminohexane in water in one beaker
- mix 1,6-hexanedioyl dichloride in an organic solvent
- pour one solution on top of the other and if you’re careful not to mix them, you get 2 distinct layers and nylon is formed where these layers meet
- extract this later by slowing lifting it out of the beaker with tweezers and collecting is by wrapping the nylon, which forms a thread, around a rod
How do chemical cells work?
- have an exothermic reaction within in the cell that develops a p.d between the 2 ends = when cell connected to a circuit then a current flows through the cell and the circuit
What are fuel cells?
- electrical cells that produce electricity through a chemical reaction between a fuel and O2 without combustion occurring
- it uses the energy from the reaction between them to produce electrical energy efficiently
What happens when hydrogen and oxygen react?
- produce water (2H2 + O2 —> 2H2O)
- reaction is exothermic so releases energy
- when new bonds formed = excess heat is given out
- e.g. hydrogen oxygen fuel cell combine H2 and O2 to release heat and nice clean H2O (no pollutants) as they use exothermic reaction b/w them but it is split into 2 reactions
How do hydrogen-oxygen fuel cells work?
1 = hydrogen into anode and oxygen into cathode 2 = at negative electrode, Hydrogen molecules lose e- to produce H+ ions (oxidation) 3 = H+ ions pass through the protons exchange membrane to the other side of the fuel cells (positive electrode) 4 = at positive electrode = oxygen gain electrons from electrode and react with H+ ions to make after vapour (reduction) 5 = e- flow through external circuit from anode to cathode (electric current) 6 = overall redox reaction
What is the electrolyte and electrodes made from in hydrogen- oxygen fuel cells?
- electrolyte is phosphoric acid is hydrogen ions travel from left to right (acidic fuel cell) but if h+ ions travel right to left (alkaline cell), then electrolyte is potassium hydroxide
- electrodes are porous carbon with a catalyst (nickel or platinum)
- hydrogen goes into anode compartment and oxygen into cathode
What is a cathode and anode in fuel cells?
Cathode is positive
Anode is negative
What happens at the cathode of a hydrogen-oxygen fuel cell?
- reduction
- O2 + 4H+ + 4e- —> 2H2O
- oxygen is reduced to make water
What are the advantages of fuel cells?
- don’t generate harmful pollutants (no CO2 emissions)
- efficient for producing energy
- lightweight
- compact
- no moving part of combustion so useful for spacecraft
What are the disadvantages of fuel cells?
- expensive to adapt out current technology to run off fuel cells
- hydrogen is difficult and expensive to extract and store (most hydrogen right now is being made through fossil fuels)
- poisonous catalysts used in fuel cells need to be disposed safely or could lead to environmental damage
What happens at the anode of a hydrogen-oxygen cell?
- oxidation
- balance = 2H2 (g) —> 4H+ (aq) + 4e-
- hydrogen is oxidised
What are the costs and benefits of fuel cells in spacecraft?
- no moving parts to maintain, small size for the amount of electricity produces, water produced can be drunk
- but must have H2 fuel and solar cells use light into electricity to carry out electrolysis of H2 (h+ into H2 and OH- into O2) but solar cells need light but fuel cells don’t
What are the benefits and costs of fuel cells in vehicles?
- less greenhouse emissions, less dependant on oil, less air pollutants, high efficiency, quieter to use
- higher vehicles cost, hard to store, not as durable as combustion engines and less filling stations
What are the costs and benefits of a petrol/ diesel vehicle?
- more durable, less price, more reliable, cheaper to maintain
- not energy efficient, not good for the environment, air and waste pollution, many moving parts
Why is it a problem if the fuel cell is quiet?
- pedestrians might not hear cars coming
What are the differences between addition and condensation polymerisation?
- addition = add together to form a polymer, repeated units without eliminating anything, uses unsaturated compounds (alkene normally), 100% atom economy - polythene, polybutene
- condensation = combines different monomers with elimination of a simple molecules (e.g. HCL or H2O), involves 2 monomers with 2 functional groups, less efficient than addition polymerisation - polyester, polyamide
Why does fractional distillation work?
- more imf = higher boiling point = more energy needed to overcome or more heat needed
Why are hydrogen oxygen fuel cells not environmentally friendly?
- fossil fuels still needed to make the hydrogen oxygen fuel cells
- hydrogen oxygen fuel cells still has poisonous catalysts
- hydrogen oxygen fuel cells releases pollutants
What are some properties of polymers?
- flexible = as it has weak imf so it’s easy for it to be overcome= can be turned into any shape
- unreactive = doesn’t react with food or water it may contain and can be used to store products
- non toxic and insoluble so can store water and can store edible products
How can an ester be made?
- heat reagents in a beaker or a test tube in water bath
- mix reagents together
- alcohols react with carboxylic acids to make esters
- can use refluxing or distillation to heat things without losing it as it has low b.p
- add sulphuric acid as a catalyst (more yield)
- add reaction mixture to sodium carbonate solution to neutralise the sulphuric acid
- safety goggles, gloves, safety screen, fire extinguisher, water baths, lab coats
What happens when you combine ethene and bromine water?
- addition reaction or bromination
- forms a dibromocompound
What is the molecular formula of sodium hydrogen carbonate?
- NaHCO3
What two reactants are needed to make Nylon 6-6?
- Aqueous 1,6-hexanedioyl dichloride - like a group of carboxylic acids but has two -COCl instead of COOH
- 1,6-diaminohexane (less dense so floats on the other) - has two NH2 groups
- interface = nylon
- eliminates HCl
What else can you use instead of 1,6-hexanedioyl dichloride for nylon in a lab?
- hexanediodic acid
- eliminates water
Explain fractional distillation in terms of intermolecular forces!
- it’s used to separate hydrocarbons into fractions
- fractions have different boiling points
- larger molecules have stronger imf and thus they have higher boiling points and vice versa
What are the features of a homologous group?
- same general formula
- same trend in physical properties
- same functional group
- same type of chemical reactions
What property of hydrocarbons depends on its size?
- boiling point
- viscosity
- flammability
What is a method of cracking?
Catalytic cracking
What is crude oil?
-mixture of lots of different hydrocarbons (mainly alkanes - CnH2n+2)
