AQA Chemistry topic 10

Transcription

1 Using Resources AQA Chemistry topic 10

2 10.1 Using the Earth s Resources and obtaining Potable Water

3 Natural Resources Some examples of natural resources. What are they used for? Wood Farming Can we replace any of these with artificial or synthetic products? Wool Fuels

4 Finite Resources Q. Are the following resources examples of finite or renewable ones? Farming Quarrying Building new homes Dumping waste

5 Sustainable Development Sustainable development is all about preserving the world for tomorrow. The main point is don t use resources at a rate quicker than they are made. For example, don t fish too much! Examples of sustainable development in fishing include: 1) Limiting the number of fish allowed in a catch (a quota ) 2) Controlling the size of the net

6 Population growth and Water The number of people on the Earth has risen dramatically in the last 100 years: What will this mean for the supply of drinking (potable) water? Water that is safe to drink is called potable water. Potable water is not pure as it contains dissolved substances but its still safe to drink as the quantities of substances are low.

7 Water Amazing facts about water: 1) 95% of your body mass is water (94% in women due to a higher body fat content) 2) Dinosaurs would have drunk the same water you do 3) Water dissolves more substances than any other liquid most ionic substances are soluble and most covalent substances are insoluble 4) Around 75% of the world s surface is made of water 5) To feel thirsty you need to lose around 1% of your body water 6) 5,000 children die every day due to not having clean drinking water 7) An average person in the West uses litres of water every day

8 Water resources There are many different water resources in the UK and the method used to make water potable depends on the source: Lakes Reservoirs Potable water is produced by: 1) Choose an appropriate source 2) Pass the water through a filter bed 3) Sterilise it with chlorine, ozone or UV light Rivers Aquifiers

9 Other ways to treat water 1) Distilling seawater to boil off clean water desalination 2) Using a membrane filter to filter out bacteria through reverse osmosis Unfortunately, both of these processes take lots of energy and are therefore expensive

10 Pollutants in water Many different pollutants can find their way into our water: Nitrates used in farming which are washed into lakes by rainwater organic matter and harmful microbes must be removed Industrial waste water may require removal of organic matter and harmful chemicals

11 Waste Water Treatment Our water supplies obviously contain various microbes and dissolved substances. To be used as drinking water it has to be treated: 1) Sedimentation 2) Filtration/screening 3) Chlorination We can also use anaerobic digestion or aerobic biological treatment of sludge/effluent.

12 Extracting and purifying copper Copper can be extracted from copper-rich ores by heating the ores in a furnace (displacing it with scrap iron) and then purifying it by electrolysis. Unfortunately, the supply of copper ore is limited. What are the possible solutions? Extracting copper uses large amounts of heat and energy Bingham Canyon copper mine in Utah, one of the largest in the world

13 New ways of extracting metals Phytomining growing that absorb metals and then them to extract the metal from. Bioleaching using to produce leachate solutions that contain metal. Q. What are the advantages and disadvantages of each method? Words compounds, plants, bacteria, burning, ash

14 10.2 Life Cycle Assessment and Recycling

15 Life Cycle Assessments (LCAs) LCAs are carried out to assess the environmental impact of products at each of these stages: Step 1: Raw materials and Manufacture What resources are needed? What effect will this have on the environment? Step 2: Use How much energy will be needed? What is the effect on the environment? Step 3: Disposal How is the product disposed of? What is the effect on the environment?

16 An example LCA Carrier Bags Q. Consider the humble plastic bag. What steps are involved in its life cycle and how can the carbon footprint of each step be reduced? Steps in the bag s life cycle 1) Drill for crude oil 2) Put the oil through fractional distillation 3) Crack alkanes to make ethene 4) Use heat to polymerise ethene 5) Transport plastic bags to shops 6) Transport bags to landfill sites Ways to reduce the pollution or environmental cost 1) Use recycled materials 2) Reduce consumption of the bags 3) Manufacture them closer to shops 4) Recycle the bags after use

17 Recycling Why recycle metals? 1) Less space will be needed for landfill sites 2) Recycled metals only need about 1/10th of the energy to produce compared to producing new metals 3) Recycling saves on raw materials plastics, glass and ceramics come from limited raw materials 4) Less excavation and mining costs Reduce, reuse, recycle!

18 Two Examples of Recycling Metal Metals can be recycled by melting and recasting into different products. Sometimes a substitute can be used, e.g. some scrap steel can be added to iron to reduce the amount of iron needed. Glass Glass bottles can be crushed and melted to make other glass products.

19 10.3 Using Materials (Chemistry only)

20 Rusting Rust is a hydrated form of iron oxide. It is formed when iron and/or steel combines with oxygen and water: Iron + oxygen + water hydrated iron (III) oxide Aluminium has an oxide coating that protects the metal from further corrosion.

21 Rusting Task: To investigate what causes rusting Tube 1 drying agent Tube 2 boiled water Tube 3 water + air Tube 4 water + air + salt

22 Rusting Task: To investigate what causes rusting No rust No rust Rust Lots of rust Iron + oxygen + water hydrated iron oxide

23 Ways to prevent rust There are several ways to prevent rust: 1) Electroplating 2) Sacrificial protection (using a more reactive metal to coat the iron) 3) Using oil or grease 4) Painting

24 Galvanising and Sacrificial Protection Galvanising is when iron is coated with a layer of zinc which stops oxygen getting to the iron and also acts as a sacrificial metal. Sacrificial protection works by using a metal that s more reactive than iron. The more reactive metal loses electrons instead of iron. Tin plating works by coating the iron in tin, e.g. in food cans. However, this only works if the tin remains intact if it is scratched the iron rusts more quickly than if it wasn t coated.

25 Alloys Steel is an alloy i.e. a mixture of metals. Here are other alloys: Gold mixed with copper, silver or zinc Aluminium mixed with magnesium and copper strong but low density Bronze is an alloy of copper and tin. Brass is an alloy of copper and zinc.

26 Gold alloys Gold can be mixed with zinc, silver or copper to make alloys with different properties. For example: 24-Carat gold 9-Carat gold Pure gold 99.99% of the atoms in this bar are gold atoms (fineness off 999.9). Pure and malleable but soft. 9 carat gold around 9/24ths of the atoms in these earrings are gold atoms. Harder than pure gold but less malleable.

27 Using impurities to strengthen Iron In pure iron all impurities are removed. This makes the iron soft: Adding 1% impurities makes the iron much stronger:

28 Making steel Strong Strength Hardness Weak 0.5% 1% 1.5% Amount of carbon added (%) Steel with a low carbon content is easily shaped Steel with a high carbon content is strong but brittle Steel with chromium and nickel is called stainless steel

29 Ceramics Most of the glass we use is soda-lime glass, made from, sodium carbonate and. We also use borosilicate glass (using boron trioxide), which has a higher point. Clay ceramics (including pottery and bricks) are made by shaping wet and then heating in a. Words furnace, clay, melting, limestone, sand

30 Polymers recap H H C C Ethene H H Here s ethene again. Ethene is called a MONOMER because it is just one small molecule. We can use ethene to make plastics Step 1: Break the double bond Step 2: Add the molecules together: This molecule is called POLYETHENE, and the process that made it is called POLYMERISATION

31 Properties of Polymers H C H H C H n Polythene. Used to make bags and crates. Can be either low density (LD) or high density (HD). H C Cl H C H n Polyvinylchloride (PVC). Used to make water pipes and coating for window frames. F C F F C F n PTFE tape. Used for nonstick coating in frying pans.

32 LD vs HD Polythene LD Polythene HD Polythene Properties: Soft, flexible Uses: bags, cling film Monomer: Ethene Reaction conditions: 200 O C, 2000 atm pressure and oxygen catalyst Properties: Hard, strong Uses: buckets, pipes Monomer: Ethene Reaction conditions: 60 O C, 2 atm pressure and a Ziegla- Natta catalyst

33 More about Polymers 1) Some plastics have intermolecular forces between each molecule these have melting points. These are thermosoftening polymers. 2) Some plastics have forces between each molecule. These have melting points and are. These are called thermosetting polymers. Words high, low, strong, weak, rigid

34 Composites A composite material is a material made from two other materials. Fibres or fragments of one material (the reinforcement ) are surrounded by a material called a binder or matrix. Some examples: Composite material Matrix/ binder Reinforcement fibre/fragment Uses Concrete Cement and water Sand and crushed rock Buildings Composite wood (e.g. plywood) Adhesives Wood fibres Buildings, furniture Natural wood Lignin Cellulose fibres Buildings, furniture Carbon fibre composites Polymer Carbon fibres or nanotubes Sports equipment

35 10.4 The Haber Process and use of NPK Fertilisers (Chem only)

36 Reversible Reactions recap Some chemical reactions are reversible. In other words, they can go in either direction the reactants will make the products and the products will then make the reactants again: A + B e.g. Ammonium chloride NH 4 Cl heat cool C + D Ammonia + hydrogen chloride NH 3 + HCl The direction of the reaction can be affected by changing the conditions

37 Reversible Reactions and energy changes If a reaction is EXOTHERMIC in one direction what must it be in the opposite direction? endothermic A + B C + D exothermic Q. Which direction would you push the reaction in if you heated it up? If a reaction is endothermic, it wants to take in energy. Therefore, by heating it, you help it. For example, consider copper sulphate: Hydrated copper sulphate (blue) endothermic + Heat Anhydrous copper + Water exothermic sulphate (white) CuSO 4.5H 2 O CuSO 4 + H 2 O

38 Reversible Reactions and Equilibrium When a reversible reaction occurs in a CLOSED SYSTEM (i.e. no reactants are added or taken away) an EQUILIBRIUM is achieved in other words, the reaction goes at the same rate in both directions (a dynamic equilibrium ): A + B C + D Higher Tier only - What happens if we change the conditions of an equilibrium? What does it do to a reaction? Henry Le Chatelier, We can use Le Chatelier s Principle to work out how changes in concentration, temperature and pressure will affect an equilibrium. My principle is: If the system is at equilibrium and a change is made, the system responds to counteract the change. Here s the idea:

39 Le Chatelier s Principle 1 Concentration (HT only) Consider a reaction where reactants A and B make products C and D: A + B C + D If the concentration of reactant A was increased, the system is no longer at equilibrium. More products will be formed to restore the equilibrium (and vice versa).

40 Le Chatelier s Principle 2 Temperature (HT only) Increasing the temperature of a system basically means giving the system energy, i.e. you will help an endothermic reaction: Endothermic reactions Increased temperature: Exothermic reactions Increased temperature: A + B C + D A + B C + D More products Less products Decreased temperature: Decreased temperature: A + B C + D A + B C + D Less products More products

41 Le Chatelier s Principle 3 Pressure (HT only) Consider a reaction where nitrogen and hydrogen are used to make ammonia: Q. How many molecules are on this side of the equation? Nitrogen + hydrogen Ammonia N 2 + 3H 2 2NH 3 How many are on this side? A. 4 A. 2 An increase in pressure will push the reaction towards the side with the lower number of molecules (i.e. you ll make more ammonia). A decrease in pressure will make more hydrogen and nitrogen.

42 Making Ammonia Guten Tag. My name is Fritz Haber and I won the Nobel Prize for chemistry. I am going to tell you how to use a dynamic equilibrium in a reversible reaction to produce ammonia, a very important chemical. This is called the Haber Process. Nitrogen + hydrogen Ammonia N 2 + 3H 2 2NH 3 Fritz Haber, You get the raw materials from the air (nitrogen) and natural gas (hydrogen). To produce ammonia from nitrogen and hydrogen you have to use three conditions: Nitrogen Hydrogen High pressure 450 O C Iron catalyst Mixture of NH 3, H 2 and N 2. This is cooled causing NH 3 to liquefy. Recycled H 2 and N 2

43 Haber Process: Economics A while ago we looked at reversible reactions: Endothermic, increased temperature Exothermic, increase temperature A + B C + D A + B C + D Endothermic Nitrogen + hydrogen Ammonia N 2 + 3H 2 2NH 3 Exothermic 1) If temperature was DECREASED the amount of ammonia formed would... 2) However, if temperature was INCREASED the rate of reaction in both directions would causing the ammonia to form faster 3) If pressure was INCREASED the amount of ammonia formed would INCREASE because there are less molecules on the right hand side of the equation

44 The Haber Process Economics How quickly ammonia is made The cost of electricity/gas Cost of reactants Cost of equipment Factors affecting the cost of making ammonia The cost of wages Catalyst Temperature Pressure

45 Haber Process Summary A low temperature increases the yield of ammonia but is too slow A high temperature improves the rate of reaction but decreases the yield too much A high pressure increases the yield of ammonia but costs a lot of money To compromise all of these factors, these conditions are used: Nitrogen Hydrogen 200 atm pressure 450 O C Iron catalyst Mixture of NH 3, H 2 and N 2. This is cooled causing NH 3 to liquefy. Recycled H 2 and N 2

46 Production and Use of NPK Fertilisers Here s a bag of NPK fertiliser. What s so special about it? Some facts: 1) NPK contains nitrogen, phosphorus and compounds 2) Use of fertiliser improves productivity 3) They are formulations of different 4) Ammonia is used to make ammonium salts and acid 5) Potassium chloride, potassium sulfate and phosphate rock are obtained by. 6) Phosphate rock cannot be used directly as a but can be treated with nitric acid or sulfuric acid to produce soluble salts that can. Words fertiliser, potassium, salts, farming, nitric, mining

47 Naming Fertiliser Salts Name the salts made by 1) Treating phosphate rock with nitric acid Calcium nitrate 2) Treating phosphate rock with sulfuric acid Calcium phosphate + calcium sulfate 3) Treating phosphate rock with phosphoric acid Calcium phosphate