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353 Cards in this Set
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Bulk chemicals |
Produced on a large scale in very large quantities Examples-ammonia,sulfuric acid, sodium hydroxide and phosphoric acid |
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Fine chemicals |
Produced on a small scale in much smaller quantities Examples-drugs,foods additives and fragrances |
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What do chemists work in a range of? |
Different roles in the chemical industry |
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What do chemists work to do? |
Research and develop new chemical products and processes |
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What does developing new products or processes involve? |
An extensive programme of research and development |
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What is one example of development? |
The development of catalysts for new processes |
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What do the government make laws and regulations to control? |
Different aspects of the chemical industry |
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What are these laws designed to protect? |
The safety of people and to reduce any impacts on the environment |
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What regulations do these laws include? |
Regulations about safety of people and to reduce any impacts on the environment |
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What are there also regulations about? |
The safe storage and transport of chemicals |
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What is the first of chemical synthesis? |
Prepare the Feedstocks(the chemicals the process uses? |
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When does synthesis happen? |
When the chemicals react together to make the product |
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What resources should sustainable processes use? |
Resources that can be replaced and do not damage the environment |
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What does sustainable processes use? |
Renewable feedstock |
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What do sustainable processes not do? |
Damage the environment at any stage of the process |
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What happens at the end of the process? |
The products are separated from the mixture |
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What needs to happens to by-products and waste? |
They need to be handled separately |
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What is checked from the product? |
The purity |
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What factors do sustainable processes consider? |
-using renewable Feedstock -finding other uses for by products -energy inputs&outputs&renewable energy use -reducing environmental impact of each stage of the prices -ensuring people's health and safety of people -social and economic benefits for people |
6 |
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What do reactions with high atom economy produce? |
Less waste |
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What does atom economy? |
The percentage the mass of the atoms in the chemicals used in a reaction that end up in the product |
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What happens in exothermic reaction? |
They give out heat energy to the surroundings Reactants lose energy when they form products |
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What do endothermic reactions? |
They take in heat energy from the surroundings The reactions take in heat energy from the surroundings Reactants gain energy when they form products |
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When is energy taken in? |
When bonds break |
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when is energy given out? |
When bonds form |
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What happens if more energy is given out than taken in? |
The reaction is exothermic |
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What happens if more energy is taken in than give out? |
The reaction is endothermic |
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What can energy changes be shown in? |
Energy level diagrams |
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What can the activation energy be shown as on an energy level diagram? |
An upwards arrow |
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What is activation energy? |
The minimum amount of energy needed to start a reaction |
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What is activation energy used to break? |
Bonds to start a reaction |
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What happens if activation energy is high? |
Very few molecules may have enough energy to start a reaction |
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What happens if the activation energy is low? |
Many more molecules may have enough activation energy to start reacting |
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What are reactions with very high activation energies usually slower than? |
Reactions with low activation energy |
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What happens if an exothermic reaction has a large activation energy? |
It may not take place at room temperature |
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How can activation energy can be supplied? |
Using a spark or heat to start the reaction |
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What do catalysts increase? |
The rate of reactions |
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Are catalysts used up or not used up in reactions? |
Used up |
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Why do many industrial processes use catalysts? |
So that the products can be made faster |
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What are different catalysts used for in industry? |
Different reactions |
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What can a catalyst work for? |
Many different reaction, but usually a particular process always uses a specific catalyst |
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Enzymes |
Biological catalysts |
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Where are enzymes found? |
In living cells |
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When do enzymes usually only work? |
As catalysts for one particular reaction |
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How do catalysts and enzymes speed up reactions? |
By providing an alternative route for the reaction |
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What does a reaction that uses a catalyst have? |
A lower activation energy than the same reaction without a catalyst |
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What do catalysts work across? |
A much broader range of conditions that enzymes |
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Why can industrial processes that use enzymes only work under a narrow range of conditions? |
Enzymes are very sensitive to reaction conditions |
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How do enzymes and catalysts increase the sustainability of industrial processes? |
Some reactions with high atom economy are too slow to be used in industry, using catalysts increase the the rate, means the reactions with high atom economy can be used in industry |
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How can using a catalyst save energy and costs in industrial processes? |
Using catalysts and enzymes means that the reaction can happen at a lower temperature |
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When do enzymes denature? |
When their shape changes doe to a change in conditions |
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Why can the enzyme not work if the shape changes? |
It is the wrong shape to bind to reacting molecules |
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What happens during a chemical reaction? |
Bonds are broken and forned |
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What must happen for a reaction to start? |
There must be enough energy available to break bonds |
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What happens if the energy given out when bonds are formed is more than the energy taken in to break bonds? |
The overall reaction is exothermic |
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When is the overall reaction endothermic? |
If the energy given out when bonds form is less than the energy taken in to break bonds |
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Why do different reaction have different activation energies? |
Different bonds need to be broken |
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What do different types of bonds have? |
Different bond energies |
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What can the energy change during a reaction be worked out from? |
The bond energies of all the bond in the reactants and products |
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How do you work out the amount of energy given out when all of the bonds in the products form? (Step 1) |
-make a list of bond in the products -work out how many of each type of bonds there are in products -to work out the total energy for each bond, multiply the number of each bond by the bond energy -add all the bond energies together |
4 steps |
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How do you work out the amount of energy taken in to break all of the bonds inbred reactants? (step 2) |
Same as step 1 but the reactants bonds are worked out, not the productd |
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How do you work out the energy given out in an exothermic reaction? |
Energy given out making bonds-energy taken in breaking bonds |
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The value of the energy change show? |
The energy given out in a reaction |
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Where is the RAM of an element shown? |
On the periodic table |
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What is the relative atomic mass? |
The mass of an atom compare do the the mass of carbon atom with a mass of |
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What is the relative formula mass? |
The mass of a molecule or formula unit of a compound It is also measured relative to the mass of a carbon atom with a mass of 12 |
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How is the relative formula mass worked out? |
By adding together the relative atomic masses of every atom in the formula |
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What is the RFM of chlorine(diatomic) |
35 (17.5*2) |
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What can the relative masses of the reactants and products in an equation be used to work out? |
The actual masses of reactants used and products formed |
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What are the stages for working out the actual masses of reactants used and products formed? |
-work out the RAM and RFM of each reactant or product involved in the question -link the values together in a simple sentence -scale down to 1g -scale up to the values in the question |
4 steps |
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Alkanes |
Family of hydrocarbons |
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Hydrocarbons |
Compounds that contain hydrogen and carbon only with no other elements |
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What happens when alkanes burn in plenty of air? |
They make carbon dioxide and water |
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Do alkanes dissolve in water? |
No and they do not usually react with other reactants dissolved in water |
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How can Alkanes be shown? |
Using ball and stick diagrsm |
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What are the bonds between atoms in alkanes? |
They are single covalent bonds |
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Are the C-C and C-H bonds in alkanes easy or difficult to break? |
Easy |
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Why is the activation energy for reactions of alkanes high? |
Because the bonds are difficult to break |
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If the bonds of alkanes are difficult to break, what does this mean? |
Although alkanes burn, they are generally interactive and do not react with other reactant dissolved in water (aqueous solutions) |
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Why is alkanes burning an exothermic reaction? |
The energy given out during the reaction to form the bonds in carbon dioxide and water is greater than the energy taken in Energy must be taken in to break the bonds in the alkanes and oxygen to start the reaction |
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What do saturated molecules contain? |
Only single bonds between two carbon atoms |
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What do unsaturated molecules contain? |
One or more double bonds between two carbon atoms |
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What are the general formula for alkanes? |
CNH(2n+2) |
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What is the alkenes general formula? |
CnH(2n) |
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What are alcohols? |
A family of compounds |
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What is the alcohol with the smallest molecule? |
Methanol-CH3OH |
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What is methanol used as? |
A fuel and solvent |
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What is the type of alcohol in alcoholic drinks? |
Ethanol-c2h5oh |
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What is ethanol also used as? |
A fuel and a solvent |
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What functional group do alcohols have? |
-OH |
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How are oxygen and hydrogen atoms bonded by? |
A covalent bond and also bond to the rest of the alcohol molecule by a covalent bond |
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What do alcohols burn in air to make? |
Carbon dioxide and water |
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What different properties do alcohols have in comparison to alkanes? |
-alkanes are unreactive& are not soluble in water -all alcohols are soluble in water -each alcohol has a higher melting and boiling point compared to an alkane with the same number of carbon atoms |
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Why are alcohols flammable? |
Because they contain a hydrocarbon chain of carbon and hydrogen atoms |
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What is made when ethanol react with sodium? |
Sodium ethoxide and hydrogen |
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What other reaction is similar to the reaction between ethanol and sodium? |
Water and sodium |
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Is the reaction between sodium and ethanol slower or quicker than the reaction between water and sodium? |
Slower |
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Why does ethanol react with sodium? |
Because it has an-OH group |
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Why do alkanes not react with sodium? |
Because they have no -OH group |
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What is fermentation? |
A process that is used to make alcoholic drinks |
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What does yeast turn sugar into during fermentation? |
Ethanol |
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What is yeast? |
A microorganism |
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What does yeast use sugar as? |
Food to make energy |
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What are formed as waste products during fermentation? |
Ethanol and carbon dioxide |
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What equation can fermentation be represented by? |
Sugar=ethanol+carbon dioxide |
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Why must air be kept out during fermentation? |
Because ethanol is made when yeast respites anaerobically |
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What can fermentation only be used to make? |
A dilute solution of ethanol |
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When does fermentation stop? |
When the ethanol becomes more concentrated |
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What does yeast produce that causes fermentation? |
Enzymes |
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What does higher concretions of ethanol do? |
Kill the yeast |
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When is ethanol toxic? |
At higher concentrations |
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What does the ethanol produced by fermentation do to yeast? |
The ethanol is toxic to yeast, when the concentration rises, the yeast dies |
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What is yeast need to do? |
Produce enzymes for fermentation |
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What do enzymes only work in? |
A narrow temperature range, if the reaction mixture is too high or too low, fermentation stops |
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What PH do enzymes work best at? |
PH5 |
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What happens if the conditions of temp or PH are outside the optimum range for the enzymes? |
Fermentation will slow down of stop, this can happen even at low concentrations of ethanol |
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Distillation? |
A process that is used to make a dilute solution of ethanol more concentrated? |
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What are the stages of distillation? |
-dilute ethanol solution is heated just above the ethanol boiling point-78℃ -ethanol boils off &leaves most of the water behind -ethanol vapour cooled&condensed to form a liquid -liquid contains a more concentrates solution of ethanol-a spirit |
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What is distillation used to make? |
Ethanol for fuel and spirit drinks such as whisky and brandy |
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What does distillation require? |
A large amount of energy to energy to evaporate the ethanol |
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What does using energy have an impact on? |
The cost of the process and the environment |
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What did fermentation use? |
Sugar from plats grown as crops, which contain only small amounts of sugar |
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What become waste products of fermentation? |
Large amounts of unused plant material and carbon dioxide gas |
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What can be used as biomass? |
Waste plant material from agriculture |
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What are scientists developing? |
New processes to convert biomass into ethanol-some processes use genetically modified bacteria |
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How is biomass covered into ethanol? |
-plant material from a range of sources can be used -the biomass is dissolved in acids and solvents -e.coli bacterial use cellulose in the plant material as food and produce ethanol -process works just above normal temperatures |
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What is the problem with using ethanol via biomass? |
-does not work well enough to be used on a large scale -acids and solvents used to dissolve the biomass may be harmful to people or the environment -the processes are not fully developed |
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Why may biomass be sustainable in the long term? |
-plant material is renewable, the process can use waste plant material that has no other uses -conditions for the process uses little energy -eventually may be possible to convert about 90% of the plant cellulose into ethanol, giving high atom economy |
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What does crude oil contain? |
The alkane ethane |
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What can ethane be converted to? |
Ethene(a molecule with a double bond) |
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What does ethane react with to make ethanol? |
Stean |
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What is needed in the crude oil reaction? |
A catalysts |
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What should happen at the end of the crude oil process? |
Distillation is used to separate and purify the ethanol |
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What's the first stage of making ethanol from crude oil? |
Ethane reacts to make ethene and hydrogen |
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What is the second stage of the crude oil process? |
Ethane from stage 1 reacts with steam to make ethanol |
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At what temperature does the crude oil reaction happen? |
300℃ |
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What catalyst is used in the ethane with steam reaction? |
Phosphoric acid |
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What is the disadvantages of making ethanol from crude oil? |
-large amount of energy needed-high temperature needed -crude oil is not renewable |
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What are the advantages of making ethanol from crude oil? |
-high atom economy-only hydrogen is made -hydrogen-by product-has many uses -faster than fermentation |
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Carboxylic acids |
Family of organic compounds |
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What tastes do carboxylic acids have? |
Sharp, unpleasant |
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What smells do many carboxylic acids have? |
Unpleasant |
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What do carboxylic acids cause? |
The smell of sweaty socks and the taste of rancid butter |
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What chain do carboxyilic acids have? |
Hydrocarbon chain |
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What is the functional group of carboxylic acids? |
-COOH |
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What part of the molecule gives the acidic properties and of carboxylic acids? |
The -COOH functional group |
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What can the -COOH group lose to form a negative ion? |
An H+ ion |
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What die the negative ion formed from the carboxylic acid contain? |
The hydrocarbon Chain attached to -COO- |
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What do some insect and plant cells contain? |
Methanoic acid |
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What does vinegar contain? |
Ethanoic acid |
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What are the formulae for methanoic and ethanoic acid? |
Meth-HCOOH Eth-CH3OOH |
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What are all carboxylic acids? |
Typical acids-they have a low PH and they react with metal, carbonates and alkalis |
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What does a carboxylic acid that reacts with metal form? |
Salt and hydrogen |
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What is formed when carboxylic acid reacts with an alkali? |
Salt and water |
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What forms when a carboxylic acid reacts with a metal carbonate? |
Salt and water |
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What do the names of salts made by carboxylic acids end in |
-oate |
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What can acids be classified as? |
Strong or weak |
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Are carboxylic acids strong or weak acids? |
Weak acids |
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When are strong acids corrosive? |
At all concentrations |
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When are weak acids corrosive? |
At high concentrations |
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What are two examples of carboxylic acids? |
Methanoic acid, ethanoic acid |
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What is ethanoic acids used to make? |
Vinegar |
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Why ethanoic acid safe to use in food? |
Because vinegar is a dilute solution and also because ethanoic acid is a weak acid |
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Give examples of strong acids |
Hydrochloric, sulfuric and nitric acid |
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What PH do strong acids have? |
A very low PH |
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What PH do weak acids like carboxylic acids have? |
A higher ph than strong acids-closer to PH7 |
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What do all acids produce when they react? |
H+ |
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When do acid reactions almost always happen? |
When the acids are dissolved in water |
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Why do strong acids have a lower PH than weak acids? |
They produce a higher concentration of H+ ions when they dissolve in water |
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What happens when to molecules in weak acids when they dissolve in water? |
Most of the molecules do not ionise when they dissolve in water |
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What happens when ethanoic acid dissolves in water? |
Most of the molecules stay as complete molecules, only a very few molecules ionise the make H+ and CH3COO- ions |
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Are weak acids more or less reactive than strong acids? |
Less reactive |
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Do weak acids react slower or quicker than strong acids |
Slower |
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What smells and flavours do esters have? |
Fruity |
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What do natural esters give fruit and flowers? |
Their distinctive tastes or smells |
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Why do esters smells travel easily? |
They have low boiling points and evaporates quickly at room temperature |
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What are esters used as? |
Solvents |
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What is ethyl ethanoate an example of? |
An ester |
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What is ethyl ethanoate used as? |
Nail varnish remover-it acts as a solvent |
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What do some paints and inks Contain? |
Solvents that are esters |
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What is used as fruity flavourings and perfumes? |
Esters |
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What is added to plastics to make them more flexible? |
Esters-plasticisers |
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When are esters made? |
When a carboxylic acid reacts with an alcoholic |
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What are synthetic esters often cheaper to produce than? |
Natural flavouring and perfumes |
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How are different esters made? |
By reacting together different carboxylic acids with different acids |
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What two reactant make ethyl ethanoate? |
Ethanoic acid and ethanol |
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What is ethanol used as a solvent? |
Paints Glues Dyes Nail varnish remover |
4 |
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Why do conditions for this reaction needed to be adapted? |
The reaction is very slow |
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How can a mixture be sped up? |
-a catalyst is used -the mixture is heated |
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What are the four stages of making a liquid Ester? |
-heating under reflux -distillation -purification-using a tap funnel -drying |
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How do ethanol and ethanoic acid react together? |
By heating under reflux |
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What is heating under reflux used to do? |
To heat substances with low boiling points |
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What happens during heating under reflux? |
A vertical condenser is attached to a flask, the contents of the flask evaporate when they are heated but then cool down and turn back to liquids in the condenser. They drip back down into the flask and are not lost |
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What happens at the end of the reaction? |
The ethyl ethanoate needs to be separated from the mixture, this is done during distillation |
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What happens during distillation? |
The mixture is heated again, but this time the condenser is positioned at an angle, the Ester evaporates,cools &condenses in condenser and collected as it drips from the condenser. Most of the mixture is left behind in the flask, the Ester still contains impurities-unreacted acid and alcohol |
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Where can the ethyl ethanoate be purified? |
In a tap funnel, separate layers can be run out of a tap funnel |
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How are ethanoic acid impurities removed? |
By adding sodium carbonate dissolved in water, ethanoic acid&sodium carbonate react to make a salt, CO2 and H2O |
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What happens to the carbon dioxide in the reaction? |
It can be released from the top of the tap funnel |
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What do the ethyl ethanoate and water form from the reaction? |
It forms a separate layer |
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What happens to the salt in the reaction? |
It dissolves in the water and can be run off |
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How is ethanol removed? |
By adding calcium chloride dissolved in water, the ethanol dissolves in the calcium chloride and water layer and can be run off |
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What is solid anhydrous calcium chloride mixed with? |
The ethyl ethanoate, this dries the Ester by removing all of the water, the waste solid can be filtered off |
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What would the final ethyl ethanoate may have done to it? |
It may be distilled again to ensure it is pure. Only distillate that boils at the exact boiling point of ethyl ethanoate(77°) is collected |
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What states are fats at room temperature? |
Solids |
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What states are oils at room temperature? |
Liquids |
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What do living things use fats and oils for? |
Fats and oils |
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Where do fats usually come from? |
Animals |
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Where do oils usually come from? |
Plants |
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Give examples of oils from plants that are used in food |
Olive oil, sunflower oil |
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What are all fats and oils are based on? |
The glycerol molecule, but different fats and oils different structure because the fatty acids are different |
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What type of compound are fats and oils? |
Esters |
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What are fatty acids? |
Carboxylic acids with a very long hydrocarbon chain |
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What is glycerol? |
Try alcohol, it has three -OH groups |
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What do fats and oils consist of? |
Three fatty acids which link by Ester groups to the three -OH groups on the glycerol molecule |
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What does most animal fats contain? |
Fatty acids with saturated hydrocarbon chains |
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What are all the carbon atoms in a saturated hydrocarbon chain joined by? |
Single carbon-carbon bonds |
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What do most vegetable oils contain? |
Fatty acids with unsaturated hydrocarbon chains |
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What are some of the carbon Stimson an unsaturated hydrocarbon chain joined by? |
Double carbon-carbon bonds |
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What can be used as a test for unsaturation? |
Bromine water-unsaturated compounds turns bromine water from orange-brown to colourless, saturated compounds do not react with bromine water |
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What can the bromine water test also be used to tell the difference between? |
An alkane and an alkene |
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What can most chemical reaction only work in? |
The forwards direction, products cannot react to form reactants again |
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What can reversible reactions do? |
Happen in both the forwards and backwards direction |
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What can reversible reactions reach? |
Equilibrium |
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When is the only time equilibrium can be reached? |
In a closed container |
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What does the closed container make sure? |
That the reactants and products cannot escape |
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What happens at equilibrium? |
The amount of the reactants and the products stay the same(as long as the conditions stay the same) the rate of the forwards reaction is the same as the rate of the backward reaction |
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Why is equilibrium dynamic? |
Reactions continue to happen, even at equilibrium |
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What do plants need nitrogen for? |
Growth |
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What does the air contain a large amount? |
Nitrogen gas |
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What are the nitrogen compounds called that plants take in? |
Nitrates |
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What is fixing nitrogen? |
Forking nitrate compounds from nitrogen |
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What is the problem with natural nitrates? |
There are not enough natural nitrates available for growing large amounts of crops |
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Why do farmers add fertilisers to soil? |
To provide nitrates for crops |
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What are synthetic fertilisers used to provide crops with? |
Nitrogen for growth |
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How must synthetic fertilisers be made using? |
An industrial process |
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What can synthetic fertilisers cause? |
Environmental problems when they are used |
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What are synthetic fertilisers made from? |
Ammonia |
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What is ammonia made by? |
The Haber process |
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What is the Haber process named after? |
Fritz Haber, he invented the procesd |
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What is the feedstock for the Haber process? |
Hydrogen and nitrogen gas |
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What reacts together in the process? |
The hydrogen gas and nitrogen gas |
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Where does nitrogen gas come from? |
The air |
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How is hydrogen made? |
By reacting methane with steam |
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What does choosing conditions for the industrial process involve? |
Considering both the rate of the reaction and the yield of ammonia |
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What is the rate of reaction for the Haber process increased by? |
-using a catalysts -raising the temperature -increasing the pressure |
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What is the catalyst used in the Haber process? |
Iron |
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What is the temperature for the Haber process? |
450℃ |
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What is the atmospheric pressure for the Haber process? |
200 atm |
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What also affects the yield of ammonia made? |
The conditions for the process |
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Is the Haber process Exo or Endothermic? |
Exothermic |
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Why does increasing the temperature decrease the yield? |
A higher temperature increases the rate of the backwards reaction |
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Why does the reaction not reach equilibrium? |
The gases do not spend long enough in the vessel |
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Around what percentage of the nitrogen and the hydrogen react together? |
20% |
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What happens to the ammonia as the mixture leaves the reaction vessel? |
It is removed |
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What happens to the nitrogen and hydrogen that is not used? |
They are recycle, no reactants are wasted |
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What are the condition for Haber process thought of as? |
A compromise, taking into account the rate of reaction, the yield and the cost of running the process |
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Why is the compromise of the temperature what it is? |
A higher temperature increases the rate of reaction of reaction However a higher temperature decreases the ammonia yield Higher temp costs more 450℃,gives a reasonable yield and rate and is not too expensive to mantain |
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Why is the atm pressure compromised at 200? |
Higher pressure increases reaction rate and yield, very high pressure means there would more likely be a leak, very high pressure is more expensive to maintain |
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What are organic fertilisers made from? |
Waste material from animals and plants |
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Where are synthetic fertilisers from? |
Frederick in industrial processes |
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Which fertilisers are generally less soluble in water? |
Organic fertilisers |
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What do soluble fertilisers do? |
They dissolve in rainwater and can get washed into rivers |
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What do fertilisers cause algae to do? |
To grow, the algae dies&bacteria that live on the dead algae multiply, taking oxygen from the water, fish and organisms in water die from lack of oxygen |
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What does using too much fertiliser or putting fertiliser on the fields when the crops are not growing do? |
it makes the problem worse |
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What are scientist study about enzymes? |
How enzymes from bacteria fix nitrogen directly from the air to try to copy natural processes to make fertiliser, they are trying to make new fertilisers that are similar to natural organic fertilisers |
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What do natural processes that fix nitrogen involve? |
Enzymes that are made by bacteria |
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Where do nitrogen-fixing bacteria live? |
In the soil and in the roots of some types of plants |
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What are scientists using their understanding of how bacteria and then enzymes fix nitrogen to develop? |
New approaches to fertilising crops |
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What are copies of natural enzymes being developed to make? |
Fertilisers economically in processes that work at room temperature |
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What are the two types of genetically modified crops being developed? |
1) crops that can make their own enzymes to fix nitrogen 2) crops that have bacteria living in their roots to fix nitrogen |
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When is a process sustainable |
When it can meet the demands of people without causing lasting harm to the environment |
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Why may processes that rely on the use of bacteria and enzymes be more sustainable in the long term? |
They do not use as much energy They do not depend on non renewable resources |
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However what is the current limitation of processes that rely on the use of bacteria? |
The process is still experimental and do not work well enough for large scale use yet |
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Why is making fertilisers using the Haber process not sustainable in the long term? |
- methane for hydrogen is a non renewable resource-will run out -uses lots of energy for the high temperature and pressure needed -energy used for transport-product -uses large amount of water -produces lots of Co2 due to high energy use |
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What does chemical analysis involve? |
Using practical techniques to test a sample to collect information and data about the chemicals the sample contains |
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Qualitative data |
Gives information to identify which substances the sample contains |
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Quantitative datai |
Gives numerical data about the amounts of substances the sample contains |
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Why is it important measurements on each sample are repeated? |
Because outliers or errors can be identified before the data is processes |
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Why is each stage of analysis standardised so that they are the same every time? |
So that measurements can be compared |
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Why are samples of a material chosen so that they represent the bulk of the material under test? |
In practice it is not possible to test every part of a material |
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Why is great care taken when samples are prepared? |
So they avoid contamination |
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What things are done to prevent contamination? |
-gloves/mask worn -using clean equipment to collect sample -using clean container to hold sample, so it does not contain chemicals |
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Why do samples need to be carefully stored? |
So they do not deteriorate before they are tested |
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how are samples that contain bacteria may be kept? |
In a refrigerator to stop bacteria from multiplying |
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Why may freezing some samples not be suitable? |
Freezing may cause damage |
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Where can samples be stored under? |
Very dry conditions |
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Why are some samples stored under an inert gas? |
To stop oxidation by reaction with oxygen in the air |
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What is chromatography used as? |
A method of analysis that can be used for some mixtures |
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What are the two phases that all types of chromatography involve? |
Stationary phase Mobile phase |
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What does the stationary phase not do? |
Move, e.g. paper in paper chromatography |
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What does the mobile phase do? |
It moves and carries the substances in the mixture along, the substances spread out as they move |
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Why does water make a good solvent? |
Because may substances dissolve in water |
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What does an aqueous solution contain? |
Substances dissolved in water |
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What does a non-aqueous solution contain? |
Substances dissolved in other solvents e.g. ethanol |
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What does using different solvents in chromatography give? |
Different patterns because different solvents spread the substances out differently as the solvent mives |
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What does the way substances spread out depend on? |
How soluble each substance is in the solvent. More soluble substances will usually spread further |
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What is a solute? |
The substances that is dissolved in a solution |
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When may a solute be more soluble? |
In some solvents than in others |
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What are immiscible solvent? |
Solvents that do not mix, they form separate layres |
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What affects the amount of solute dissolved in solvents? |
The solvents solubility in each solvent, |
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What does the solute have a different concentration in each layer? |
More solute will dissolve in one layer of solvent than in another |
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What does the movement of the molecule of the solute between two solvent eventually reach? |
Equilibrium |
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Why does chromatography work? |
Because the substances in the mixture are distributed between the mobile phase and the stationary phase |
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What happens to the substance that is most soluble? |
It will dissolve more and be carries along the most when the mobile phase moves, this means it will travel the furthest |
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What happens to the substance that it least soluble? |
It will stay attached to the stationary phase and will move the least |
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What do substances separate depending on? |
How they are distributed between the mobile have and the stationary phase |
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What is the stationary phase in paper chromatography? |
A piece of chromatography paper |
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What is the stationary phase in thin layer chromatography? |
A plate of plastic or glass coated with a thin layer of solid-e.g. silica or alumina |
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Where is a spot of sample put? |
On a pencil line high enough to be above the layer of the solvent |
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Where is the paper or plate placed? |
In the solvent-if a non aqueous solvent is used, a lid needs to be used to stop the solvent evaporating |
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What does the solvent then do? |
Slowly rise upward, separating the substances in the spot |
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When should the plate or paper be taken out? |
Before the solvent reaches the top |
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What happens to the distance moved by the solvent? |
It is marked |
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What do coloured inks do? |
They separate out to give different spots for each substance in the mixture |
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What are referenced materials used to identify? |
The spots-this involves spotting known substances ate the same level as the spot of the unknown mixture at the start of the chromatogram |
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What can the distance travelled by the reference material spots be matched to? |
The unknown spots to identify the unknown substances in the mixture |
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What is a locating agent used for? |
To see the spots of substances that are not coloured |
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What can be used as locating agents? |
Chemicals e.g. iodine or ninhydrin UV light |
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What are Rf values calculated from? |
The distance moved by a spot |
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Give the formula for an Rf value |
Distance moved by sample/distance moved by solvent |
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What can Rf value be used to identify? |
The substances in a mixture- by comparing Rf values of unknown substances with Rf values for known substances |
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What are Rf values always the same for? |
A particular substance, as long as the same solvent is used as at the same temperature |
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When will Rf values change for the same substance? |
If a different solvent is used or the temperature is changed, this is because the solubility of the substance in the solvent will be different |
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What does gas chromatography work for? |
Mixtures that turn into a gas easily when heated |
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What is the stationary phase in Gas chromatography? |
A solid packed into a long column, the column is coiled up so that it takes up less space |
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Where are the substances moved through? |
The column by a carrier gas-which is the mobile phase |
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Why must the gas be inert? |
So that it does not react with the substances being tested |
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What gases are often used for gas chromatography? |
Nitrogen and argon |
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What is the column surrounded by? |
An oven-this heats up and controls the temperature of the column |
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What does the sample being tested contain? |
A mixture of substances |
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How are the substances spread out in gas chromatography? |
-some substances are attracted to the solid in the tube more than others -each substance carried by the gas therefore travels at different speeds -the substances spread out in the column, the ones that travel the fastest come out the end of the column first |
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What does the gas chromotogram give? |
A print out to show the time taken for each substance to travel through the column, this can be used to identify each substance |
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Retention time |
The time each substance takes to travel through the column |
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What is each substance detects by as it comes out of the column? |
The detector |
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What are these results recorded on? |
A recorded, the recorder gives a graph that shows a peak for each substance in the mixture |
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What does each substance in gas chromatography do? |
Give a peak in a different place |
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What does the height of the peak indicate? |
How much of a substance is in the mixture |
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What can a mass spectrometer do? |
Be attached to the detector-it uses the masses of the substances to identify them |
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A standard solution |
A solution of known concentration, it contains a known amount of solute dissolved in a fixed volume of solution |
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What does quantitative analysis involve? |
Taking measurements of quantities |
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What does using standard solution reduce? |
Errors |
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Why are measurements repeated? |
To try and check there are no errors in measurements |
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Outliers |
Measurements that do not fit the pattern of the other results, these can be left out of calculations if you are sure they are long |
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What does the mean give? |
The best estimate of the true value of the quantity that is being measured |
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What does the range of results give an idea of? |
The uncertainty in the accuracy of results |
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What are the stages of making a standard solution? |
-measure solute mass in a clean beaker -add distilled water and stir till it is fully dissolved -pour solution into volumetric flask using a funnel -rinse beaker and funnel with distilled water, add water to flask this makes sure no solute escapes -add more distilled water to flask until it reaches the mark -invert the flask |
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What is the mass of the solute and the volume of the final solution used to calculate? |
The concentration of the standard solution |
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What is concentration measure in? |
G/dm3 grams per decimetre cubed |
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To calculate concentration, what must your volume be in? |
DM3 |
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How do you convert CM3 into DM3? |
Divide it by 1000 |
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What is the formula for working out the concentration of a solution? |
Mass of solute/volume of solution |
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What does an acid based titration measure? |
How much acid needed to react with a base, the method makes sure that all measurements are as exact as possible |
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What are the steps of acid based titration? |
-measure known based amount,said may dissolved to make a standard solution -use pipette to measure solution -add indicator to flask -fill burette with acid, run acid through burette to make sure jet is full -add acid from burette to conical flask and swirl to mix solution -near the end, add the acid drop by drop |
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