OCR 21st Century Science C7

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  • Created by: Caroline
  • Created on: 20-06-13 09:40
What is meant by the term 'bulk chemical'? Give 2 examples.
Chemicals that are produced on a large scale. For example Phosphoric Acid and Sulfuric Acid.
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What is meant by the term 'fine chemical'? Give 2 examples.
Chemicals that are produced on a small scale. For example food additives and fragrances.
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Why do new chemical products need a lot of research? (Part 1)
The production of a new chemical may need a catalyst to be found. This is likely to involve: 1.Using trial and error to find a substance. 2.Creating a computer model of the reaction to work out what substance will work.
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Why do new chemical products need a lot of research? (Part 2)
3.Designing or refining the manufacture of the catalyst to make sure it is safe, efficient and cost-effective. 4.Investigating the problems to the environment that the catalyst will cause and trying to minimise them.
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Why do new chemical products need a lot of research? (Part 3)
5.Monitoring the quality of the product to check that the catalyst is not affecting it.
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Why does the government enforce strict regulations?
To protect both the people and the environment.
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What regulations does the government have on use of chemicals?
Eg. sulfuric acid is sprayed on potato fields to make harvesting easier by killing the stalks and leaves. The government has put a restriction on how much can be sprayed, and say that a sign has to be put up to warn the public.
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What regulations does the government have on the storage of chemicals?
Dangerous chemicals have to be stored in locked store rooms. Poisonous chemicals must either be kept in sealed containers or in well-ventilated store rooms.
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What regulations does the government have on the transport of chemicals?
Lorries that are transporting chemicals must display hazard symbols and an identification number to help the emergency services deal with accidents or spills.
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What are the stages of producing chemicals?
1.Preparing the feedstock. 2.Synthesis. 3.Seperation of products. 4.Handling by-products and waste. 5.Measuring the purity.
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What are the 8 questions that need to be asked when thinking about sustainability? (Part 1)
1.How good is the atom economy? 2.Are there any benefits or risks to society? 3.Are the raw materials renewable? 4.What do you do with the waste products? 5.Are there any environmental impacts? 6.Is it profitable?
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What are the 8 questions that need to be asked when thinking about sustainability? (Part 2)
7.Are there any health and safety risks? 8.What are the energy inputs and outputs?
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What is an exothermic reaction?
A reaction where energy is given out as bonds are made.
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What is an endothermic reaction?
A reaction where energy is taken in as bonds are broken.
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Work out the overall energy change for: H-H + Cl-Cl --> H-Cl H-Cl. Bond energies: H-H:436kJ/mol, Cl-Cl:242kJ/mol, H-Cl:431kJ/mol.
Bond breaking: 436+242=678kJ/mol. Bond making: 431+431=862kJ/mol. 678-862=-184kJ/mol.
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Is this reaction exothermic or endothermic? How can you tell?
Exothermic, the answer is negative meaning energy is given out.
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What is activation energy?
The minimum energy needed to break the bonds and start a reaction.
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What happens if the energy input is lower than the activation energy?
The bonds won't break so the reaction won't start.
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What is a catalyst?
A substance which speeds up the rate of reaction without getting used up.
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What does a catalyst do regarding energy?
A catalyst lowers the activation energy by providing alternative routes.
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What happens to the overall energy change when a catalyst is used?
It stays the same as when a catalyst is not used.
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What is a reversible reaction?
A reaction where the products can themselves react to form the original reactants.
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What is the sign for a reversible reaction?
Too half arrows pointing in opposite directions, one on top of the other.
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In what conditions is an equilibrium formed?
In a closed system. This means that none of the reactants or products can escape.
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What is an equilibrium?
The relative (%) quantities of reactants and products will reach a certain balance and stay there.
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What is a dynamic equilibrium?
Reactions are taking place in both directions at the same rate, so they cancel each other out meaning that the overall effect is nil.
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What type of reaction happens in the Haber Process?
Reversible.
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What is the balance symbol equation for the Haber Process?
N2 + 3H2 ---> 2NH3.
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What are the feedstocks for the Haber Process?
Nitrogen and Hydrogen.
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Where do these come from?
Nitrogen is easily obtained from the air as it is 78% Nitrogen. Hydrogen comes from the cracking of chemicals in natural gas using steam.
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Why don't the gases reach equilibrium in this process?
They don't stay in the reaction vessel long enough.
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Does all of the nitrogen and hydrogen react?
No.
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What happens to the nitrogen and hydrogen that don't react?
They are recycled and sent back round to the start of the system to start the process again.
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What does this process produce?
Ammonia.
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What conditions are needed for this process?
Temperature: 450 degrees C. Pressure: 200 atmospheres.
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Which substance is used as a catalyst?
Iron.
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What compromises need to be made with the pressure used in this process?
Higher pressures favour the forward reaction (since there are 4 molecules on the right but only 2 on the left.) So the pressure is set as high as possible to give the best % yield, however a compromise has to be made to make it affordable.
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What compromises need to be made with the temperature used in this reaction?
As the reaction is exothermic, increasing the temperature will actually shift the equilibrium in the opposite direction, so lower temperatures give a better yield. However this makes a slow rate of reaction so a compromise is made to increase this.
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What is nitrogen fixation?
The process of turning nitrogen in the air into useful nitrogen compounds like ammonia.
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What happens to most of the ammonia produced by nitrogen fixation in the Haber Process?
Used to make fertilisers which are used to grow crops. It is also used in industry to make plastics, pharmaceuticals and explosives.
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What is the problem with using fertilisers?
They can cause eutrophication.
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What is eutrophication? (Part 1)
The fertilisers get washed into the rivers by the rainwater. This causes an algal bloom on the surface which blocks off the sunlight to the water underneath. The plants underneath the surface die as they cannot photosynthesise without sunlight.
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What is eutrophication? (Part 2)
Bacteria decompose the dead plants, using up the oxygen. The oxygen is not replaced as there are no plants carrying out photosynthesis, so the organisms, such as fish, under the water suffocate and die.
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What do nitrogen-fixing bacteria do? How do they do this?
Fix nitrogen at room temperature and pressure by using biological catalysts called enzymes.
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Why do chemists want to create a catalyst that mimic these enzymes?
So that the Haber Process can be carried out at room temperature and pressure. This would make it both cheaper and safer.
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Is Nitrogen Fixation a sustainable process? (Part 1)
1.Atom Economy:Excellent as all the nitrogen and hydrogen is used. 2.Social Impacts: Helps world food production. 3.Are the raw materials renewable?: Hydrogen comes from fossil fuels so will eventually run out.
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Is Nitrogen Fixation a sustainable process? (Part 2)
4. Waste Products: There are no waste products. 5.Environmental Impacts: Fertilisers can get into water systems and cause eutrophication. 6.Is it profitable? Yes, makinng ammonia is a big business.
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Is Nitrogen Fixation a sustainable process? (Part 3)
7.Health and Safety Risks: Working at high temperatures and pressures can be dangerous. 8.Energy Inputs and Outputs: A lot of energy is needed to maintain the conditions of 450 degrees C and 200 atmospheres.
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What are alkanes?
A family of hydrocarbons.
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What type of bonds do they contain?
Single covalent bonds between carbon atoms.
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Are they saturated or unsaturated? Why?
Saturated. No more bonds can be made as there are no double convalent bonds to be broken.
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What is the formula for an alkane?
CnH2n+2.
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What are the first 4 alkanes?
Methane, Ethane, Propane, Butane.
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What do alkanes burn to give?
Carbon dioxide and water.
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Do alkanes react with chemicals?
No they don't react with most chemicals. They don't react with aqueous reagants. This is because the C-C bonds and the C-H bonds are hard to break.
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What is the functional group of alcohols?
-OH
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What do all alcohols end in?
-ol.
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What is the formula for an alcohol?
CnH2n+1OH
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Why do all alcohols have similar properties?
Because of their -OH functional group.
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What are the similarities and differences between alcohols, alkanes and water? (Part 1)
Ethanol and water are good solvents. Ethanol is soluble in water, alkanes are not. The boiling point of ethanol is 78degrees, of water 100degrees, and of a similar sized alkane -103degrees. Ethanol is a liquid at room temperature and is volatile.
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What are the similarities and differences between alcohols, alkanes and water? (Part 2)
Methane and ethane are also volatile, but they are gases at room temperature. Water is a liquid at room temperature but it is not volatile.
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Give a use of ethanol and a use of methanol.
Ethanol is used in perfumes and aftershave lotion as it reacts with both the water and the oil. Methanol is used in industry as a starting point for the manufacture of other chemicals.
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What is the reaction between sodium and ethanol?
Sodium + Ethanol ---> Sodium Ethoxide + Hydrogen.
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What is the reaction between sodium and water?
Sodium + Water ---> Sodium Hydroxide + Hydrogen.
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Which reaction is more vigorous?
Sodium and Water.
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Do alkanes react with sodium?
No.
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What are the 3 ways of making ethanol?
Fermentation of sugar, fermentation of waste biomass and using ethane.
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Explain how ethanol is made by the fermentation of sugar. (Part 1)
Yeast ferment the sugar to produce ethanol and carbon dioxide. Yeast contains zymase, which is used as the catalyst in this reaction. The reaction happens best at 30degrees C and pH 4, as this is when the zymase works the best.
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Explain how ethanol is made by the fermentation of sugar. (Part 2)
If the conditions are not correct the process will not be carried out as the zymase will be denatured. It is important that oxygen does not get to the process as the ethanol will react to form ethanoic acid which will lower the pH.
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Explain how ethanol is made by the fermentation of sugar. (Part 3)
This stops the enzymes from working. There is a limit to how concentrated the ethanol can be, as once it gets to about 10-20%, the yeast will be killed off by the ethanol and the process will stop.
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What is done to the ethanol once it has been created by fermentation of sugar?
It is distilled to increase the concentration.
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Explain how the ethanol is distilled. (Part 1)
The ethanol is put into a flask below a fractionating coloumn. The solution is heated so that the ethanol boils. The ethanol vapour travels up the column, cooling as it goes.
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Explain how the ethanol is distilled. (Part 2)
The temperature is such that anything with a boiling point of ethanol, eg. water, cools to a liquid and flows back down into the flask. The ethanol vapour flows through the condenser where it is turned into a liquid and collected.
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Is fermentation of sugar a sustainable process? (Part 1)
Atom Economy: Low due to waste carbon dioxide. Social Impacts:Doesn't impact society. Renewable resources?:Sugar beet and yeast can be grown quickly so will not run out. Waste Products:Carbon dioxide is simply released into the atmosphere.
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Is fermentation of sugar a sustainable process? (Part 2)
Environmental Impacts: Carbon Dioxide is a greenhouse gas so will add to global warming. Profitable?:It depends on what the ethanol is used for. Heath+Safety:No specific dangers. Energy:Needed to control conditions.
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Explain how ethanol is produced by fermentation of waste biomass.
Waste biomass is all the bit of the plants and crops that aren't used. Yeast will not ferment waste biomass as it contains cellulose. E.coli bacteria can be genetically modified so that they will ferment it. Optimum conditions: 35degreesC and pH6.
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Is this method sustainable?
Similar to fermentation of sugar as they are similar processes. However this method is cheaper as crops don't have to be grown specially for this.
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Explain how ethanol is produced using ethane.
Ethane is a hydrocarbon found in crude oil and natural gas. It can be cracked to form ethene and hydrogen. The ethene then reacts with steam to produce ethanol. Optimum conditions: 300degreesC and 70 atmospheres. Catalyst:Phosphoric acid.
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Is this method sustainable? (Part 1)
Atom Economy: Fairly high as hydrogen is the only waste product. Social Impacts:None. Renewable Resources?:Crude oil is not renewable so will run out. Waste products:Hydrogen can be used in the Haber Process.
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Is this method sustainable? (Part 2)
Environmental Impacts: Hydrogen is not harmful. Crude oil can through oil spills. Profitable?:Method is continuous and cheap. Health+safety:High temperatures need to be controlled. Energy:Needed to control conditions.
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What is the functional group for Carboxylic Acids?
-COOH.
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What do all of their names end in?
-anoic acid.
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What are the first 4 carboxylic acids?
Methanoic acid, Ethanoic acid, Propanoic acid, Butanoic acid.
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What is the reaction between a carboxylic acid and a reactive metal?
CA + Metal ---> Salt + Hydrogen.
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What is the reaction between a carboxylic acid and a carbonate?
CA + Carbonate ---> Salt + Water + Carbon Dioxide.
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What is the reaction between a carboxylic acid and a hydroxide?
CA + Hydroxide ---> Salt + Water.
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What do the salts formed by carboxylic acids end in? Give an example of a reaction.
-anoate. eg. Methanoic acid + Magnesium ---> Magnesium methanoate + hydrogen.
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What type of acids are carboxylic acids?
Weak.
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Finish the sentence. The pH of a dilute carboxylic acid is...
Higher than the pH of a dilute strong acid.
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What smells and tastes are carboxylic acids responsible for?
The smell of smelly socks and the taste of rancid butter.
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What happens to wine and beer if it is left out in the air?
The ethanol reacts with oxygen to form ethanoic acid.
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What is vinegar?
A dilute solution of ethanoic acid.
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What is the functional group of esters?
-COO-
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How are the formed?
When a carboxylic acid and alcohol react.
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How do you name an ester?
Alcohol followed by carboxylic acid.
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How do you remember this?
You drink lots of alcohol and then you are sick.
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What do you need in order to start off this reaction? Give an example.
A strong acid catalyst. Eg. concentrated sulfuric acid.
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What are esters used for?
1.Esters are responsible for the fruity smells and tastes of fruit. 2.They are volatile which makes them idea for perfumes. 3.To make fragrances+aromas. 4.Solvents(in paint, glue, nail varnish remover). 5.Plasticisers.
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What are fats and oils esters of?
Glycerol and fatty acids.
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What are fatty acids?
Carboxylic acids with long chains. Can be between 16 and 20 carbon atoms.
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What is glycerol?
An alcohol.
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When fats and oils are produced, what are they mostly made up of?
Fatty acid chains.
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Are fatty acids saturated or unsaturated?
They can be either.
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Why are fats a good store of energy?
They have lots of energy packed into them.
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What does an organism do when it has too much energy?
Stores it as fat so it can be used at a later date when they need more energy.
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Explain the difference between the fat made by plants and animals.
Animals: Make animal fats. Mainly saturated with very few C-C double covalent bonds. They are usually solids at room temperature. Plants: Make vegetable oil. Mainly unsaturated with lots of C-Cdouble covalent bonds.Usually liquid at room temperature.
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What are the stages for making an ester?
1. Heating under Reflux. 2.Distillation. 3.Purifcation. 4.Drying.
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Explain heating under reflux.
Eg. To make ethyl ethanoate: Ethanol and ethanoic acid is put in a flask under a condenser. It is gently heated so the vapour rises. The condenser catches the vapours and takes them back down into the flask so they have time to react.
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Explain the distillation process.
The mixture is heated below a fractionating column. As it starts to boil, the vapour enters the fractionating column. When the temperature at the top of the column reaches the boiling point on ethyl ethanoate, it travels down the condenser+collected.
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Explain the purification process. (Part 1)
The liquid collected is poured into a tap funnel. A sodium carbonate solution is added and it is shaken. The water does not react with the ethyl ethanoate so two layers are formed. The bottom layer is tapped off.
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Explain the purification process. (Part 2)
The remaining upper layer is shaken with concentrated calcium chloride solution to remove any remaining ethanol. This again seperates into two layers and the bottom layer is tapped off.
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Explain the process of drying.
Lumps of anhydrous calcium chloride is added to the mixture. This absorbs the water. It is then filtrated to remove the calcium chloride and pure ethyl ethanoate is formed.
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What is a qualitative analysis?
It tells you what substances are in a sample.
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What is a quantitative analysis?
It tells you how much of a substance is in a sample.
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Why is chemical analysis carried out on samples?
1. If something goes wrong you can take another sample. 2.It is easier than using a large amount.
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What must you make sure when using a sample?
That it is representative of the bulk of material, otherwise the results are not reliable.
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How are samples usually analysed?
In solution.
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What are the two types of solution?
Aqueous - Water. Non-aqueous - anything other than water. eg. ethanol.
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What is a standard procedure?
Clear instructions that tell you how to carry out a task.
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Why are they important?
They ensure the task is being done safely, efficiently and cost-effectively. They give reliable results.
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What are the two phases in Chromatography?
Mobile Phase: The molecules can move. Always a liquid or gas. Stationary Phase: The molecules cannot move. Usually a solid but can be a really thick liquid.
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Describe the process of paper chromatography. (Part 1)
A baseline is drawn on the stationary phase (chromatography paper). This is put in a flask holding the mobile phase (solvent). A dot of the unknown sample is placed on the baseline. The sample dissolves in the stationary phase.
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Describe the process of paper chromatography. (Part 2)
The molecules are constantly moving between the stationary and mobile phases. The chemicals seperate out as the mobile phase moves across the stationary phase. How quickly a chemical moves depends of how it 'distributes'itself between the two phases.
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Describe the process of paper chromatography. (Part 3)
If it spends more time in the stationary phase, meaning it is more soluble and less attracted to the paper, it will travel further up the chromatography paper.
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Describe the process of paper chromatography. (Part 4)
A dynamic equilibrium is reached, as the number of molecules leaving the stationary phase for the mobile phase is the same as the number of molecules leaving the mobile phase for the stationary phase.
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Describe the process of paper chromatography. (Part 5)
Before the solvent reaches the top of the paper, it is removed. The result is a chromatogram.
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What is thin layer chromatography?
Very similar to paper chromatography. The mobile stage is a solvent, eg. ethanol. The stationary phase is a piece of glass with a thin layer of solid, eg.silica gel, spread on top.
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How can you identify chemicals that are colourless?
By using locating agents. Eg. you may spray the chromatogram with a reagent.
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What is the Rf value?
The ratio between the distance moved by the solute and the distance moved by the solvent.
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What is the formula for working out the Rf value?
Rf = Distance travelled by solute/distance travelled by solvent.
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What is the line called that the solvent reaches?
The solvent front.
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Where is the distance travelled by the solvent measured from?
The base line.
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How can you identify the chemicals present in a sample?
Put dots of known samples next to it and compare the Rf values.
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Why do chemists use standard reference materials?
To check the identities of the substance.
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What are the two phases in gas chromatography?
Mobile: Unreactive gas. (eg Nitrogen). Stationary: A viscous liquid, such as oil.
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Describe the process of gas chromatography. (Part 1)
The unknoiwn sample is injected into a long tube coated on the inside with the stationary phase. The mixture moves along the tube with the mobile phase until it comes out of the other end.
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Describe the process of gas chromatography. (Part 2)
Like in the other methods, the molecules distribute themselves between the two phases.
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What is the retention time?
The time it takes for takes for the sample to pass through the tube.
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What form is the chromatogram for this process?
A graph.
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What does each peak represent?
A different substance.
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What does the peak height show?
How much of the substance is in the sample.
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What does the distance along the x-axis show?
The retention time. This can be looked up to see which substance it is.
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What is the formula for concentration?
Concentration = mass/volume.
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How many cm3 are there in a dm3?
1000cm3 = 1dm3.
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What does g/dm3 measure?
Concentration.
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How do you make up a standard solution? (Part 1)
1.Find out the mass of the solute you need using mass = conc.x volume. 2.Carefully weigh it out, weighing and recording the flask first. 3.Add a small amount of distilled water to the solute, and stir until dissolved. 3.Pour into a volumetric flask.
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How do you make up a standard solution? (Part 2)
4.Rinse the stirring rod and beaker with distilled water and add this to the solution too to ensure none of the solute is left behind. 5.Top the solution up to the desired amount using distilled water. (Ensure the bottom of meniscus is on the line.)
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How do you make up a standard solution? (Part 3)
6.Put the stopper on and shake to mix the solution. 7. Check the bottom of the meniscus is still on the line and top up if necessary.
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How do you carry out a standard acid-alkali titration? (Part 1)
1.Add a known amount of alkali to a beaker. 2.Fill a burette with acid. 3.Add indicator to the alkali. 4.Add the acid to the alkali in small amounts, swirling in between to fully mix the solution. 5.Once the end point is near, slow down.
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How do you carry out a standard acid-alkali titration? (Part 2)
6.Once the indicator has changed colour, all of the alkali has been neutralised.
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Why do you need to take several readings when doing a titration? (Part 1)
1.The first titration is a rough titration, so the second one can be done with small intervals to get a more accurate result. 2.Sometimes outliers occur due to human error or faulty equipment. These need to be done again to get rid of them.
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Why do you need to take several readings when doing a titration? (Part 2)
3.A mean value needs to be calculated.
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What is the degree of uncertainty?
A range of + or - 0.2cm3.
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What are the steps for working out the identity of an unknown element in a compound? (Part 1)
1.Use mass = concentration x volume to work out the mass of the two compounds. 2.Work out the relative formula mass of the known element. 3.Write a balanced symbol equation for the reaction.
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What are the steps for working out the identity of an unknown element in a compound? (Part 2)
4.Divide the mass of the known element by the relative formula mass. 5.Divide the mass of the unknown element by this number. 6.Identify the element using the periodic table.
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