- Alkanes are a family of hydrocarbons
- they contain single covalent bonds
- METHANE, ETHANE, PROPANE AND BUTANE are all ALKANES
- the general formula for an alkane is CnH(2n+2)
- All alkanes end in ...ANE
- Alkanes burn to give CARBON DIOXIDE +WATER
- ALKANE + OXYGEN ----> CARBON DIOXIDE + WATER
- Alkanes dont react with most chemicals this is because the C-C bonds and the C-H bonds are unreactive
QUESTIONS ABOUT ALKANES!
1) what is an alkane?
2) do alkanes have ionic bonds or covalent bonds?
3) Name the four alkanes
4) i) what do alkanes burn to give? ii) what is the general equation for this reaction?
5)why dont alkanes react with most chemicals?
1) family of hydrocarbon 2) single covalent bond 3) methane, ethane, propane, butane
4) i) carbon dioxide and water. ii) ALKANE + OXYGEN ----> CARBON DIOXIDE + WATER
5) The C-C bonds and the C-H bonds are unreactive
- functional group is -OH, this gives all alcohols similar properties
- The general formula for an alcohol is CnH2n+1OH
- all alcohols end in ......OL
- the two main alcohols are :METHANOL and ETHANOL
similarities and differences between, alcohols, al
Alcohol Alkanes Water
Ethanol is soluble in water Insoluble in water ---
Ethanol is a good solvent --- Water is a good solvent
The boiling point of ethanol Much lower boiling point The boiling point of water
is lower than water than both water and ethanol is higher than ethanol
liquid at room temp Gas at room temp liquid at room temp
volatile Volatile Not volatile
- functional group is -COOH, the functional group gives the simal properties
- their names end in -anoic acid, the two main carboxylic acids are methanoic acid and ethanoic acid
carboxylic acids react like other acids
- CARBOXYLIC ACID + METAL --> SALT + HYDROGEN
- CARBOXYLIC ACID +ALKALIS ---> SALT + WATER
- CARBOXYLIC ACID +CARBONJATE --> SALT +CARBON DIOXIDE +WATER
- Carboxylic acids are weak acids they dont react as fast as strong acids
- they have strong smells and tastes.
- if wine and bear are left open they will oxidise and will taste like vinegar
ETHANOL +OXYGEN ---> ETHANOIC ACID +WATER
energy transfer in reactions
- gives out energy to the surroundings usually in the form of heat
- an exothermic reaction can be found be an increase in temperature
- a way of remembering this is:
- EXO- exit
- THERMIC- heat
- Takes in energy from the surrondings usually in the form of heat
- an endothermic reaction is usually seen by a decrease in temperature
EXOTHERMIC ENERGY LEVEL DIAGRAM
- the products are always below the reactants this is because it gives out energy (energy is lost) meaning there will be less energy toward the end.
- the downwards arrow shows the change of energy (the energy change between the reactants and products.
- in an Exothermic reaction the change in energy will always have a minus sign before it as energy is lost.
- remember that in exothermic reactions energy is TAKEN AWAY and u will be fine.
ENDOTHERMIC ENERGY LEVEL DIAGRAM
- In Endothermic reactions the products are always above the reactants this is because endothermic reactions take in energy meaning that there will be more energy towards the end of the reaction.
- the upwards arrow shows the change in energy between the reactants and products.
- As stated before Endothermic reactions are opposite to Exothermic reaction so the energy change for endothermic will not have a minus sign in frond.. because energy id ADDED into the reaction. (+)
- The mininum amount of energy need to start a reaction
- if the energy input is less that the activation energy then the reaction wont have enough energy to start with.
- a way to remember activation energy is to think of it as a slide, first have to walk up the stairs (the activation energy) before you can start to slide down again.
What is a catalyst ? A catalyst is a substance which changes the speed of a reaction, without being changed or used up in the reaction.
- a catalyst lowers the activation energy, it does this by providing a faster route.
- The overall energy change stays the same.
- The graph above shows how the catalyst provides a different route and how it lowers the activation energy.
- during a chemical reaction only bonds are broken or bonds are formed.
- Exothermic is where bonds form
- Endothermic is where bonds break
- bonds form
- energy is released when new bonds are formed
- in an exothermic reaction the energy releasedby forming bonds is greater than the energy used to break them
- bonds break
- energy is supplied to break existing bonds
- in an endothermic reaction the energy supplied is greater that the energy released by forming them.
- a reversible reaction is one where the products of the reaction can react to form the original reactants
- reversible reactions will reach an equilibrium if it takes place in a closed system ( meaning a reaction where none of the products or reactants can escape)
- equilibrium means: the relative % quantities of reactants and products will reach a certain balance and stay there
- dynamic equilibrium means that the reactions are still taking place in both directions, but the overall effect is zero because the forward and reverse reactions cancel out each other.
- ^ the reactions are taking place at exactly the same rate in both directions. ^
Ionisation of weak acids
- Ionisation of WEAK ACIDS is a reversible reaction
- when acids dissolve in water they ionise, when they ionise they release hydrogen ions, H+. this is what makes them acidic
- acids either ionise completely or reach a dynamic equillibrium
1) strong acids (e.g. hydrochloric acid) ionise almost completely in water. this means that almost every hydrogen is released- so there are lots of H+ ions
e.g. HCl(aq) -----> H+ + Cl-(aq)
2) weak acids (e.g carboxylic acids) ionise very slightly. only some of the hydrogen in the compund is release- so there are few H+ ions
e.g. CH3COOH(aq) <====> H+(aq) + CH3COO-(aq)
- the ionisation of weak acids is a reversible reaction. since only a few H+ ions are released, the equillibrium is mainly towards CH3COOH. meaning that its not a dynamic euillibrium. it is an equillibrium towards the left.
- tells you what a sample contains
- it tells you which substances are present in a sample
- tells you how much of a substance is present in a sample
- it can be used to work out the molecular formula of the sample
you usually analyse a sample of the material under test this is because:
- it might be difficult to measure all of the material if there is a lot of it
- you might want to test a small bit so that you use the rest for something else
- taking a sample means that if anything goes wrong you can go back and use another sample
- a sample must represent to bulk of the material being tested, if it didnt it wont tell you anything
samples are usually tested in a solution,it is made by dissolving the sample in a solven, there are two types of solutions, these are:
- aqueous: the solvent is water and it is shown by the state symbol (aq)
- non aqueous: the solvent is not water, e.g. ethanol (alcohol)
standard procedures on chemical analysis
- scientist follow standard procedures - these are clear instructions which describe exactly how to carry out the practical tasks
- they are chosen because they are the safest, most effective and most accurate methods to use
- standard procedures can be agreed with a company, nationally or internationally
- they are useful because wherever and whenever a test is done, the results should always be the same- it should give reliable results every time
- ther are standard procedures for :
- collection -storage of a sample -and how it should be analysed
The two phases of chromatography
- Chromatography is an analysis method thats used to separate the substances in a mixture, indentify them and to purify them.
there are two types of phases involved in chromatography:
- mobile phase: where the molecules can move, this is always the liquid or the gas
- stationary phase: where the molecules cant move. can be the solid or thick liquid
- the mobile phase moves across the stationary phase.
- how quickly the substance moves depends on the position of the equillibrium, if the equillibrium favours the mobile phase it will move faster
- the molecules of each chemical contnuously move between the mobile and stationary phase
- they reach a dynamic equilllibrium which is when the amount leaving the stationary phase in the same as the amount leaving the mobile phase.
- stationary phase : chromatography paper
- mobile phase: solvent (ethanol or water)
1) the bottom of the paper is placed in a beaker containing the solvent
2) the solvent moves up the paper
3) `the chemicals in the sample dissolve in the solvent and move between both phases
4) in the mobile phase they move up the the paper with the solvent
5) before the chemicals reach the top the paper is removed from the beaker
- the chemicals that spend more time in the mobile phase are further up the paper. the amount of time spent at each phase depends on:
-how soluble they are in the solvent - how attracted they are to the paper
- TLC is short for Thin layer chromatography
- it is very similar to paper chromatography but the stationary phase is a thin layer of solid.
- the mobile phase is a solvent such as ethanol (alcohol), just like in paper chromatography
gas chromatography is used to analyse unknown substances.
- the sunstance has to be a gas, it is isnt it would have to be vapourised
- mobile phase: unreactive gas such aas hydrogen
- stationary phase: a viscous (thick) liquid like oil
1) the unknown mixture is injected into a tube coated on the inside with the stationary phase
2) the mixture moves along the tube with the mobile phase until it comes out the other end, the substances are distributed between the phase.
RETENTION TIME: the time it takes for the chemical to travel through the tube
RETARDATION FACTOR VALUE (Rf)
The results of a chromatography analysis is called a chromatogram
distance tarvelled by substance
distance travelled by solvent
the Rf value is the ratio between the distance travelled by the dissolved substance and the distance travelled by the solvent
There are five stages involved in producing useful chemical from the raw materials
1) raw materials are converted into FEEDSTOCKS
- feedstock are the actual reactants needed for the process, the raw materials need to be purified to make the feedstock
- the feedstock are converted into products
3) The products are separated
4) The purity of the product is monitored
5) The bi-products and waste are dealt with
- other products made in the reaction might be useful aor waste so they need to be dealt with, some are sold, used again or thrown away.
Questions asked about sustainability
1) it it a profitable method?
2) will it cause any harm to the environment?
3) how good is the atom economy? (atom economy tells you how much mass of reactants ends up as useful products)
4) what are the health and safety risks?
5) are there any benefits/ risks to the society?
6) what are the energy cost?
7) what to do with the waste-product?
8) will the raw materials run out?
MAKING ETHANOL BY FERMENTATION
- The ethanol in alcoholic drinks is made by fermentation
- the fermentation uses yeast to convert sugars into ethanol
- SUGAR (glucose) ----------> ETHANOL + CARBON DIOXIDE
- The yeast cells contain zymase which is an enzyme. fermentation happens fastest at 30 degrees this is because zymase works best at this temperature, because it is an enzyme if this temp was increases it would be destroyed. zymase also works best at PH4, if it was strongly acidic or alkaline it will not work.
- its important to prevent oxygen from getting into the reaction, this is because oxygen converts ethanol into ethanoic acid which lowers the PH and prevent the zymase from working
- when the concentration of ethanol reaches 10 to 20% the fermentation stops because the yeat gets killed of by the ethanol.
If fermentation a sustainable process?
- 1) will the raw materials run out? sugar beet and yeast grow quickly and won't run out.
- 2) how good is the atom economy? the waste CO2 means it has a low atom economy, and because the enzyme is killed of by the ethanol produced it is even less efficient.
- 3) what to do with the waste products? the waste CO2 can be released without any processing.
- 4) what are the energy costs? energy is needed to keep the reaction at its optimum temp.
- 5) will it damage the environment? yes, carbon dioxide is a green house gas and will add to global warming.
- 6) if there any health + safety risks? the chemicals and processes have no specific dangers.
- 7) are there any benefits or risks to the society? making ethanol doesnt impact society ( drinking it does)
- 8) is it profitable? this depends on what ethanol id used for, drinking or fuel?