Chemistry Unit 2: Analysing substances

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How is paper chromatography used to identify food additives?
The solution soaks up into the paper and carries the different colourings and each colour separates and stops in different positions
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How can you tell if the additives are safe?
The spots from the substance we are testing will be in line with spots from pure and safe solutions
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What are the advantages of using instrumental methods for analysing substances?
Its faster, much more accurate and more sensitive so you only need a small amount of sample.
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How does gas chromatography separate chemicals?
A gas carries the sample mix through a column which is packed with a solid material, each chemical travels at a different speed through the material so the chemicals come out of the column at different times and is put into a graph
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What what information can we gather from a gas chromatography graph?
The number of peaks tells us how many chemicals there are, the time each sample takes is called the retention time which can be used to identify each chemical.
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How is mass spectrometry used to work out the unknown chemicals?
The molecular ion peak (the right hand peak) tells us the relative formula mass of a chemical
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What is an acid?
An acid is always dissolved in water, they always release the H+ ion in water which is the ion which makes acids acidic
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What is a base?
Bases are metal oxides and metal hydroxides.
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What is an alkali?
Alkalis are metal hydroxides that are soluble in water, in water they release the OH- ion which makes alkalis alkaline
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What are the pH values of acid, neutral and alkaline solutions?
The pH value of an acid is between 1-6, the pH of a neutral solution is 7 and the pH of an alkaline solution is between 8-14
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What is a soluble salt?
Salts contain a metal part and a non-metal part, soluble salts will dissolve in water
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How does acid + metal = soluble salts
MASH : acid + metal -> salt + hydrogen e.g. 2HCl(aq) + Zn(s) -> ZnCl2(aq) + H2(g)
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How does acid + insoluble base = soluble salts
BAWS : acid + base -> salt + water e.g. H2SO4(aq) + CuO(s) -> CuSO4(aq) + H2O(l)
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How does acid + alkali = soluble salts
AAWS: acid + alkali -> salt + water e.g. HCl(aq) + NaOH(aq) -> NaCl(aq) + H2O(l)
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How do we crystallise the salt formed?
We can crystallise the salt once the reaction is finished by evaporating the water
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What is the equation for neutralisation?
H+(aq) + OH-(aq) -> H20(l)
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How do you make an insoluble salt?
Mix two soluble salts together e.g. AgNO3(aq) + NaCl(aq) -> AgCl(s) + NaNO3(aq)
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What is a precipitate?
A precipitate is a solid formed when two solutions are missed together, it can be separated by filtration. One use of precipitate is water purification where we remove unwanted ions from drinking water from sewage
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What is electrolysis?
When you pass an electrical current through a molten ionic compound to break it down into its elements
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What is an electrolyte?
An electrolyte is the molten (or in solution) ionic compound that we pass the electrical charge through
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What happens at the positive electrode (anode)?
The negative ions are attracted, these ions lose electrons and are oxidised
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What happens at the negative electrode (cathode)?
The positive ions are attracted, these ions gain electrons and are reduced, we only get a metal formed if it is less reactive than hydrogen
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What is electroplating?
Electroplating is where we make an object into a negative electrode and the positive ions move towards it and stick to it e.g silver and copper
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How is aluminium produced by electrolysis?
The Al3+ ions move towards the cathode gaining 3 electrons so are reduced forming an aluminium metal, the O2- ions are attracted to the anode and lose 2 electrons forming oxygen gas so are oxidated, the oxygen react with the graphite to form CO2
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What is the half equation of the electrolysis of aluminium?
Al3+ + 3e- -> Al
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What are the uses of aluminium?
Aircraft and cans
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What happens at the electrodes in the electrolysis of sodium chloride solution?
The Na+ is more active than the H+ so the H+ goes to the cathode and form hydrogen gas, Cl- is attracted to anode and forms chlorine gas
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What are the uses of the products of the electrolysis of sodium chloride?
The chlorine gas is used in plastics and bleach, the sodium hydroxide is the solution left over made from the Na+ and OH- ions and is used for making soap
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What is the half equation of the hydrogen gas?
2H+ + 2e- -> H2(g)
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What is the half equation of the chlorine gas?
2Cl- -> Cl2(g) + 2e-
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How do we measure the rate of reaction?
The gradient of the graph
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What four factors increase the rate of reaction?
A catalyst, concentration, temperature and surface area
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Other cards in this set

Card 2

Front

How can you tell if the additives are safe?

Back

The spots from the substance we are testing will be in line with spots from pure and safe solutions

Card 3

Front

What are the advantages of using instrumental methods for analysing substances?

Back

Preview of the front of card 3

Card 4

Front

How does gas chromatography separate chemicals?

Back

Preview of the front of card 4

Card 5

Front

What what information can we gather from a gas chromatography graph?

Back

Preview of the front of card 5
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