1. C2 – Science Wednesday 13th June 2018
Key Revision Points

2. Calculating RoR Calculate RoR using: (HT ONLY)  Need to draw
a gradient on curve and calculate RoR (e.g.)
Factors that affect RoR
Concentration
Temperature
Pressure
Surface Area
Catalyst

3. Req. Practical 5 - RoR
Changes in Concentration affects rate of reaction  measured by volume of gas collected/produced (H2, O2) or colour change (CO2) Can simply use metal + acid to collect gas (Hydrogen, Oxygen or Carbon Dioxide) DV – Volume of gas collected or time taken for colour change (i.e. cloudy) IV – Concentration of any other factor CV – All other factors that are not the IV (see list from previous slide) – use words like volume rather than amount! Repeatability/Reproducibility/Resolution! Be specific how are you measuring volumes? What are the issues? Getting bung on quick enough? Knowing when it has turned cloudy?

4. Collision Theory & Activation Energy
Chemical reactions happen  when particles with enough energy collide  the minimum amount of energy required is called the Activation Energy Increasing (i) concentration (ii) pressure (iii) surface area  increases the frequency of collisions  so increases RoR Increasing temperature  (i) increases the frequency of collisions (ii) also the collisions are more energetic  so increase the RoR Remember  by making reactants smaller  you increase SA:Volume ratio  so increase RoR  by increasing frequency of collisions Catalysts  are not used up in the reaction  they provide a different pathway for reaction  which has lower AE  therefore increasing RoR

5. Reversible Reactions
When products can react to produce the original reactants the reaction is called REVERSIBLE (know the double arrow!) Changing conditions Example 1 (if heated Ammonia is produced, if cooled ammonium chloride is produced) Example 2 (in endothermic reaction anhydrous copper sulphate is produced, but if it is exothermic hydrated copper sulphate is produced) If the apparatus prevents any products/reactants escaping  equilibrium is reached  when the forward and reverse reactions occur AT THE SAME RATE

6. Le Chatelier’s Principle (HT Only)
Reversible Reactions  Changing Concentration Reactant concentration is increased  more product will be formed Product concentration is decreased  more reactants will react Reversible Reactions  Changing Temperature If temperature is increased (i) more product for endothermic reaction (ii) less product for exothermic reaction If temperature is decreased (i) less product for endothermic reaction (ii) more product for exothermic reaction Reversible Reactions  Changing Pressure Pressure increases  equilibrium will shift to side with smaller number of molecules Pressure decreases  equilibrium will shift to side with larger number of molecules *In all cases the opposite will be true if talking about reactants or products!

7. Crude oil & Alkanes
1. Finite resource in rocks  made from ancient biomass  mainly plankton  buried in mud. 2. Mixture of compounds  mainly hydrocarbons  made from Hydrogen and Carbon ONLY 3. Most hydrocarbons found in crude oil are ALKANES  Structure, formula, names 

8. Fractional Distillation
Crude oil hydrocarbons  separated by fractional distillation  into fractions (each fraction contains similar number of C atoms)  used for fuels (diesel petrol, kerosene etc.) & feedstock in petrochemical industry Also produced are solvents, lubricants, polymers + other synthetic carbon compounds Process 1. Crude oil – vaporised (heated up and evaporates) 2. Condenses at differing boiling points 3. Producing more useful fractions

9. Properties of Hydrocarbons
Top of fractionating column  small molecules of hydrocarbons (small carbon chains)  (1) low B.P. (2) high flammability (3) low viscosity  requires little energy to break hydrocarbons Bottom of fractionating column  large molecules of hydrocarbons (long carbon chains)  (1) high B.P. (2) low flammability (3) high viscosity  requires lots of energy to break hydrocarbons Complete Combustion of hydrocarbon fuels The carbon and hydrogen is oxidised  produces CO2 and H2O Examples are below  this is where balancing simple equations will be required!!

10. Cracking & Alkenes (basic)
Alkanes (hydrocarbons)  made more useful by being broken down (cracked)  into ALKENES
Cracking occurs: (1) passed over hot catalyst OR (2) mixed with steam and heated to very high temperatures
Test for ALKENE  Add Bromine water (more reactive than Alkanes)
Goes from orange-brown to colourless (not clear) if Alkene is present
Uses for alkenes
High demand for small fuel molecules (e.g. camping gas)
Used for polymers (e.g. plastics)
Starting materials for making other chemicals
Need to be able to balance cracking equations – i.e. put in the small numbers  each side must equal the other! (see below e.g.)

11. Pure substances & Formulations
Pure substance  single element or compound  not mixed with any other substance Everyday pure substance  substance nothing added to it (e.g. milk) Elements & compounds  melt and boil at specific temp. The presence of an impurity  lowers MP and raises BP  the greater the impurity the bigger the difference between the true MP and BP Formulations Formulation  mixture – made as a useful product The are made  carefully mixing correct volumes  so product has required properties (e.g. fuels, cleaning agents, medicines, alloys and foods)

12. Chromatography XP RP 6
Can be used to separate mixtures and identify substances.
Involves a (i) stationary phase (ii) mobile phase  separation depends on the distribution of substances between the phases
So (colour dot) / movement water solvent
Chromatography XP – Method Below
Filter paper
Draw a pencil line (2cm above)
across the paper
3. Use a capillary tube to place
A sample onto the line
4. Pour solvent (water) in the bottom
Of beaker not above the pencil line
5. Allow solvent to climb up the filter
paper, separating the sample mixture
6. Stop XP when solvent doesn’t move
Or when the solvent reaches the 1cm away
From the top.

13. Gas Tests
Hydrogen test Burning splint  pop sound is produced Oxygen test Glowing splint  relights in Oxygen Carbon Dioxide test Lime water turns cloudy from being colourless (NOT CLEAR!!) Chlorine test Litmus paper  turns white and becomes bleached

14. Atmosphere Current atmosphere (last 200mill yrs)
80% Nitrogen 20% Oxygen 0.03% Carbon Dioxide
(+ variable water vapour and noble gases)
Early Earth Atmosphere
Differing theories as we are talking about 4.6 billion yrs ago!
First billion yrs  intense volcanic activity  released gases and water vapour into atmosphere  condensed and formed oceans
Earth’s atmosphere is similar to atmospheres of Mars/Venus  mainly carbon dioxide and little Oxygen
Volcanoes produced nitrogen that gradually built up in atmosphere with small amounts of methane and ammonia
When oceans formed CO2 dissolve in water and carbonate precipitates produced sediments  reducing CO2 in atmosphere

15. O2 & CO2 in atmosphere
Oxygen INCREASE in atmosphere [our friend  PHOTOSYNTHESIS!] Algae started  photosynthesis  2.7bn yrs ago Over next Billion years – plants evolved and added more Oxygen Carbon Dioxide DECREASE in atmosphere Algae + plants took in CO2 by photosynthesis. Formation of sedimentary rock and fossil fuels decreased CO2 Formation of Coal  Huge swampy forests  dead plant material  with heat and pressure and no air Formation of Oil & Gas  Formed from dead marine organisms  with heat and pressure and no air

16. Greenhouse Effect Greenhouse gases  maintain temperatures on Earth
Carbon dioxide, water vapour, methane
Greenhouse Effect
EM waves pass through the atmosphere from the sun
Earth absorbs Short-Wave EM radiation  warms up
Heat is radiated back out as Long-Wave IR Radiation
This Long-Wave IR Radiation is absorbed by Greenhouse Gases
Therefore the atmosphere warms up too
Remember the greenhouse effect is naturally occurring, but by adding greenhouse gases  it intensifies the effect  and leads to global warming

17. Human Activities on Global Climate Change
Burning (combustion) of fossil fuels & Cattle/Rice production
Increase in emissions of CO2 and Methane
Based upon Peer-review evidence  many scientists believe that human activity  has lead to increase in emissions.
But it is difficult to model such complex systems as global climate change  by simplifying or speculating about it  leads to biased coverage (media)
Effects of global climate change
Agriculture  desertification/flooding  crop yields set to decrease  weather patterns changing
Temp. increase  ice caps melt  flooding of deltas and low-lying land where people live
Populations may suffer from drought or flooding
Bird migration patterns change – habitats destroyed

18. Carbon Footprint Carbon Footprint
(DEF)  Total amount of carbon dioxide and other greenhouse gases emitted over the full life cycle of a product, service or event.
Reducing Carbon Footprint
Car pooling & public transport  spreads emissions over more riders
Using renewable resources rather than fossil fuels
Insulating the home
Using energy efficient bulbs
Eat locally-produced and organic food
The problem is political, costs and will to change lifestyles

19. Atmospheric Pollutants
Combustion of fuels When a fuel is burnt it can release  CO2, water vapour, carbon monoxide, sulphur dioxide and oxides of nitrogen Soot can be produced  unburnt hydrocarbons (incomplete combustion)  form particulates in atmosphere Carbon Monoxide Toxic gas  colourless and odourless  not easily detected Sulphur Dioxide & Oxides of Nitrogen Respiratory problems and Acid rain Particulates Global dimming and heath problems for humans

20. Earth’s Resources
Earth’s resources  warmth, shelter, food and transport Natural resources + agriculture  provide food, timber, clothing and fuels Finite resources (fossil fuels) + oceans + atmosphere  processed to provide energy and materials Sustainable Development Development that meets the needs of current generations without compromising the ability of future generations to meet their own needs New synthetic materials These replace natural materials  e.g. uPVC (synthetic polymer) windows replacing wooden windows (that rot and require painting) Fertilisers are used to supplement agricultural crops  increase yield

21. Potable Water
Drinking water  should have low levels of dissolved salts + microbes  this is called potable water  it is not pure water! (it contains dissolved substances)
Potable water produce by (method 1)
Sedimentation (large particles)
Fine filtering  filter beds (small particles)
Sterilising --> sterilising agents (e.g. chlorine)  kill microbes
If fresh water is limited  desalination of salty/sea water (method 2)
This can be done by (i) distillation or
(ii) processes that use membranes such
as reverse osmosis  although these
require huge amounts of energy

22. RP 8 - Water Purification
Test for (i) pH and (ii) presence of dissolved solids & (iii) distillation of sea water then check if dissolved solids have been removed
pH (i)
(i) Pour 1cm of different water types into test tube (ii) add UI solution (iii) record pH
Dissolved solids (ii)
Weigh dry watch glass – record mass
Add 5cm3 of water type into watch glass
Place above boiling water in beaker (acts
Like a water bath)
(4) Wait till the water evaporates, dry the
underside with cloth and then re-weigh watch glass
(5) Calculate the difference between (watch glass + solids – watch glass) = dissolved solids

23. RP 8 - Water Purification
Distillation of Sea Water (iii)
Set up apparatus as shown, conical flask, delivery tube, bung,
bunsen burner, test tube, beaker
(ii) Should be ice + water in beaker surrounding
test tube so condensation can occur
(iii) Heat the sea water until it boils  reduce
heat so gently boils
(iv) Distilled water will collect in cooled test tube
(v) Collect around 5cm3
(vi) Use the collected distilled water and perform the previous XP (i) and XP (ii) and compare to other types of water

24. Water Waste Treatment
Lifestyles + industry  Large amount of waste water
Agricultural waste and sewage  require removal  (i) organic matter (ii) harmful microbes
Industrial waste water  require removal  (i) organic matter (ii) harmful chemicals
Sewage treatment – Method
Screening and grit removal
Sedimentation to produce sewage sludge/effluent
Anaerobic digestion of sewage sludge
Aerobic biological treatment of effluent
It easiest to get water from ground water as waste and salt water require lots of energy.

25. Extracting Metals (HT Only)
Metals ores are limited
Copper ores are scarce  replacement of traditional methods of digging, moving and disposing of rock
Phytomining
Plants absorb metal compounds
Plants are harvested to produce ash that contain metal compounds
Bioleaching
Uses bacteria  produce leachate solution  contain metal compounds
The metal compounds produced by these two processes can be extracted by (i) displacement using scrap iron (ii) electrolysis

26. Life Cycle Assessment
LCA’s  assess environmental impact of products in each of these stages:
Extracting and processing raw materials
Manufacturing and packaging
Use and operation during its lifetime
Disposal at the end of its useful life (inc. transport and distribution)
It is easier to allocate numerical values to use of water, resources, energy and some waste.
It is harder to allocate numerical values to pollutant effects  requires value judgements  so could be biased (i.e. advertising purposes)

27. Reducing Use of Resources
Reducing use, reuse and recycling by end users  reduces use of limited resources, use of energy sources, waste and environmental impacts Metals, glass, building materials, plastics  produced from limited raw materials  The energy comes from limited resources. Obtaining raw materials from Earth (quarrying/mining) causes environmental impacts Examples of Re-use and Recycling Glass bottles  can be reused  crushed + melted  make new glass Metals  recycled  Melting + recasting + reforming  new metal products (some scrap steel + iron from blast furnace  reduce the amount of iron required to be extracted from iron ore)