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AQA Chemistry GCSE Topics 6-10


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[Front]


State the collision theory
[Back]


For a chemical reaction to occur, the reactant molecules must collide with enough energy

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AQA Chemistry GCSE Topics 6-10 - Details

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State the collision theory
For a chemical reaction to occur, the reactant molecules must collide with enough energy
Activation energy definition
The minimum amount of energy needed for particles to react
Name the factors for increasing rate of reaction
Increasing temperature, increasing pressure, increasing surface area, adding a catalyst
What effect does temperature have on rate reaction?
Increasing temperature means: Particles move faster Particles collide more frequently More collisions creates more energy, increasing rate of reaction
What effect does pressure have on rate reaction?
Increasing pressure means: More particles in a set volume Particles collide more frequently More collisions creates more energy, increasing rate of reaction
What effect does surface area have on rate reaction?
Increasing surface area means: Higher surface to volume ratio Particles collide more frequently More collisions creates more energy, increasing rate of reaction
What effect does a catalyst have on rate on reaction?
Using a catalyst means: Provides an alternative reaction pathway with lower activation energy Activation energy needed decreases Reaction happens faster increasing rate
Equation to calculate rate of reaction
RofR = Amount of reactant or product formed/Time
Give 3 ways (excluding the equation) to measure rate of reaction
Disappearing mark through solution, change in mass (usually gas given off), volume of gas given off
Method for investigating effect of concentration on R of R by volume of gas produced [Method 1]
Set volume of dilute HCl acid in conical flask placed on mass balance Add magnesium ribbon and plug flask with cotton wool Start stopwatch and measure initial mass Take mass reading at regular intervals Plot on a graph [Loss in mass/Time] Repeat with different acid concentrations
Independent, dependent and control variables for concentration experiment Method 1
Independent- concentration of acid Dependent- Loss in mass Control- Volume of acid, mass of magnesium ribbon
Method for investigating effect of concentration on R of R by change in colour [Method 2]
Set volume of dilute sodium thiosulphate in conical flask on paper with black X Add dilute HCl and start stopwatch Measure amount of time it takes for X to disappear Repeat reaction with different concentrations of either reactants [only one at a time]
Independent, dependent and control variables for concentration experiment Method 2
Independent- concentrations of reactants Dependent- Time for X to disappear Control- Volume of reactants, black X
Conclusion for experiment
The higher the concentration, the faster the rate of reaction.
Mean rate of reaction =
Change in y / change in x
Reversible reaction definition
A reaction where the products can react to form the reactants
Name 2 reversible reactions
Ammonium chloride <=> Ammonia + hydrogen chloride Nitrogen + Oxygen <=> Nitric acid
Dynamic equilibrium definition
When both forward and backward reactions are happening at the same time but there is no overall effect
Define Le Chatelier's principle
If the conditions of a reversible reaction are changed at equilibrium, the system [where the reaction takes place] will try to counteract the change
Effect of changing temperature in a reaction system
Decreasing: Reaction shifts to exothermic direction to produce more heat More products for the exothermic reaction than the endothermic Increasing : Reaction shifts to endothermic direction to reduce heat More products for endothermic reaction than the exothermic reaction
Effect of changing the pressure in a reaction system
Increase: Equilibrium tries to reduce pressure Moves in direction where there are fewer molecules of gas Decrease: Equilibrium tries to increase pressure Moves in direction where there are more molecules of gas
Effect of changing the concentration in a reaction system
Any change in concentration: System tries to bring itself back to equilibrium Increase in reactants causes an increase in products Decrease in products causes a decrease in reactants
What is a hydrocarbon?
Any compound formed from only carbon and hydrogen atoms
What is crude oil?
A mixture made up of hydrocarbons of different lengths
What happens to the properties of hydrocarbons as chain length increases?
Become more viscous, less volatile, less flammable, higher boiling points
What are alkanes?
Saturated compounds with a C-C single bond
What are the first 4 alkanes?
Methane, Ethane, Propane, Butane
What is the equation for complete combustion of a hydrocarbon?
Hydrocarbon + oxygen ---> carbon dioxide + water + energy
Method of fractional distillation [for Crude oil]
Oil is heated until most is a gas Gases enter fractionating column Longer hydrocarbons with higher boiling points condense back into liquids and drain out of column early near the bottom Shorter hydrocarbons with lower boiling points condense and drain out later near the top of the column Mixture is separated into fractions containing hydrocarbons with similar numbers of carbon atoms
Method of cracking [catalytic]
Vaporise long chain hydrocarbons Vapour passed over hot powdered aluminium oxide as a catalyst Molecules split apart on the surface of the catalyst
What are alkenes?
Unsaturated compounds that have a double C=C bond
When is hydrogen added to an alkene?
In the presence of a catalyst
When is an alcohol formed?
When an alkene reacts with steam and water is added in the presence of a catalyst
What are the uses of alkenes?
Alcohols, plastics, fuels, detergents
What are polymers?
A molecule comprised of long chains of monomers
What is addition polymerisation?
Where unsaturated monomer molecules open up their double bonds and join together to form polymer chains
What are the first 4 alcohols?
Methanol, Ethanol, Propanol, Butanol
What is the mobile phase?
Where molecules can move
What is the stationary method?
Where molecules cannot move
What is an Rf value?
The ratio between the distance travelled by the dissolved substance [solute] and the distanced travelled by the solvent
Rf =
Distance travelled by substance [e.g ink spot] / distance travelled by solute [water or ethanol]
What is the test for chlorine?
Bleaches damp litmus paper
What is the test for oxygen?
Relights a glowing splint
What are the tests for carbon dioxide?
Puts out a lit splint Turns limewater cloudy when bubbled through
What is the test for hydrogen?
Creates a squeaky pop when lit splint held at the end of test tube containing hydrogen
Test for carbonate ions?
Add HCl acid to mystery solution connected to limewater If carbonate ions are present, carbon dioxide is formed turning the limewater cloudy
Test for sulphate ions?
Add HCl and Barium chloride solution to mystery solution If white precipitate is formed, sulphate ions are present
Test for halides?
Add dilute nitric acid and silver nitrate solution to mystery solution If chloride is present, white precipitate is formed If bromide is present, cream precipitate is formed If iodide is present, yellow precipitate is formed
Flame tests method
Sterilise platinum loop wire in HCl and blue flame Dip loop in sample and put in flame Record flame colour and sterilise Repeat with different samples
Metal hydroxide test
Add sodium hydroxide to mystery compound forming insoluble hydroxide If coloured precipitate is formed this allows the metal to be identified
Aluminium precipitate colour
White then colourless
Composition of today's atmosphere
Approx: 80% nitrogen, 20% oxygen, small amounts of other gases
Composition of early atmosphere
Mostly carbon dioxide, minimal oxygen, nitrogen and small amounts of methane and ammonia
Theory of how early atmosphere formed
Surface covered in volcanoes that erupted releasing lots of gases
How did the early atmosphere become the present atmosphere?
Water vapour condensed forming oceans Oceans dissolved carbon dioxide Oxygen levels built up over time from photosynthesis
Describe non/renewable resources from the earth and atmosphere
Crude oil and fossil fuels from compressed layers of dead animals and sediment Geothermal power, hydropower, wind power, biomass
Potable water definition
Water safe for consumption
Potable water definition
Water that is safe for consumption
How is potable water produced?
Water is filtered through wire meshes to remove solids Water is then sterilised to kill harmful bacteria
Method to desalinate sea water
Test pH with pH meter Neutralise water if pH is too high or low with titration Complete a flame test to test for sodium ions [sodium chloride] If present flame will be yellow, so add dilute nitric acid and silver nitrate solution Heat in a distillation apparatus Water will evaporate leaving salts behind, and will condense into potable water Retest pH to ensure water is neutral
Differences in treatment waste water, salt water, ground water and sewage water
Waste water- must remove organic matter and harmful microbes Salt water- must be pH tested and distilled Ground water- filtered and sterilised Sewage water- must go through screening, sedimentation and anaerobic digestion
Phytomining definition
Where metals are extracted from their ions which are absorbed by plants through their roots
Bioleaching definion
Extraction of metals from their ores through the use of living organisms
Describe the process of phytomining
Plants absorb mineral ions Plants are harvested and burned producing ash Acid is added to ash to produce leachate Copper can be obtained through displacement with scrap iron
Describe the process of bioleaching
Bacteria are used to break down ores to produce leachate Copper ions in leachate are displaced by scrap iron
Advantages and disadvantages of phytoming
It is a slow process Reduces need of mining Conserves limited supply of high-grade ores Reduces rock waste
Advantages and disadvantages of bioleaching
Produces toxic substances Reduces need for mining Conserves high-grade ores Reduces rock waste
Purpose of the Haber process
Used to make ammonia for fertilisers
Haber process reaction
Nitrogen + hydrogen <=[iron catalyst]=> ammonia + heat N2 + 3H2 <=> 2NH3 + heat
When is the yield of ammonia higher?
When the temperatures are lower
What does the iron catalyst do?
Increase rate of reaction, doesn't affect yield
What is the trade off between rate of reaction and position of equilibrium?
Lower temperatures means the rate of reaction is slower and equilibrium is reached more slowly
What limits the Haber process commercially?
Expense of equipment to contain process safely, temperature of process and pressure process is completed under
What are NPK fertilisers?
Formulations of various salts including nitrogen, phosphorus and potassium at specific percentages
Describe the composition of NPK fertilisers
Comprised of nitrogen, phosphorus and potassium in specific percentages
How are NPK fertilisers made?
In the Haber process
How is ammonium sulphate [a fertiliser] made in a lab?
Drops of methyl orange indicator added to a set volume of ammonia sulfate solution in a conical flask Dilute sulfuric acid is added until turns orange When volume of sulfuric acid added is recorded then neutral ammonia sulfate with indicator is thrown away Experiment is repeated without indicator with same volumes of sulfuric acid and ammonia Ammonium sulfate is crystallised and then dried