What is a solvent?
A liquid that will dissolve a solid.
What is a redox reaction?
- when electrons are transferred
- loss of electrons is oxidation
- gain of electrons is reduction
What is a displacement reaction?
- a more reactive metal will displace a less reactive metal from its compound
- the metal ION always gains electrons and is reduced
- the metal ATOM always loses electrons and is oxidised
what is the word equation for rusting of iron?
Iron+oxygen+water->hydrated iron(III) oxide
Why is rusting of iron a redox reaction?
- iron loses electrons when it reacts with oxygen, each Fe atom loses 3 electrons to become Fe3+. Irons oxidised
- oxygen gains electrons when it reacts with iron, each O atom gains 2 electrons to become O2-. Oxygens reduced
How can you prevent rusting?
- iron can become an alloy by mixing it with other metals such as carbon
- by coating the iron with a barrier of paint or oil or grease
- by tin plating, acts as barrier stopping water and oxygen reaching surface of iron
What is the sacrificial method used to stop iron rusting?
- you place a more reactive metal with iron so water and oxygen react with that instead of iron
- galvanising is a coat of zinc
- blocks of magnesium can be bolted to iron
What is electrolysis?
- breaking down of a substance using electricity
- electric current is passed through dissolved ionic compound, causing it to decompose
- this creates flow of charge through electrolyte
- positive ions in solution will go to cathode and gain electrons
- negative ions in solution go to anode and lose electrons
What happens at the cathode and anode with a molten electrolyte of lead iodide, Pbl2?
Cathode: -lead produced -Pb2+ +2e-->Pb Anode: -iodine produced -2l->l2+2e-
What happens at the cathode and anode with a molten electrolyte of potassium chloride, KCl?
Cathode: -potassium produced -K+ + e- -> K Anode: -chlorine produced -2Cl- ->Cl2 +2e-
What happens at the cathode and anode with a molten electrolyte of aluminium oxide, Al2O3?
Cathode: -aluminium produced -Al3+ + 3e- ->Al Anode: -oxygen -202- -> O2 + 4e-
What does the amount of product made during electrolysis depend on and how can you increase it?
- the number of electrons that are transferred
- can be increased by electrolysing for a longer time and increasing the current
What is the equation to work out the amount of product formed during electrolysis?
Q=It
Charge=current x time
They are directly proportionate
What are fuel cells?
-electrical cells that combine hydrogen and oxygen to give out energy in an exothermic reaction
What is the equation at the anode and cathode and overall for the redox reaction of fuel cells?
Cathode: reduction -O2+4e-+2H2O-> 4OH- Anode: oxidation -2H2+4OH- -> 4H2O+4e- Overall: redox -2H2+O2-> 2H2O
What are the advantages of fuel cells?
- more efficient than power stations
- direct energy transfer
- fewer places for energy to be lost as heat
- energy isn’t lost through friction
- no pollution
What are disadvantages to fuel cells?
- energy to produce hydrogen may come from non renewable fossil fuels
- often contain poisonous catalysts which eventually have to be disposed off which is expensive and may cause environmental problems
Why are hydrogen-oxygen fuel cells used in spacecraft?
- readily available from the spacecraft rocket fuel tanks
- lightweight and compact so they don’t take up valuable room
- don’t have moving parts that could go wrong
- some product of reaction is used as drinking water
Why are fuel cells used in the car industry?
- don’t produce carbon dioxide, nitrogen oxides, sulfur dioxide, carbon monoxide
- large amounts available for use as a fuel
Why did scientists believe CFCs were good at first?
- non toxic, non flammable and chemically inert, insoluble and low boiling points
- used as coolants in fridges and air con
- used as propellants in aerosol spray cans
How do scientists discover the truth about CFCs?
- chlorine can help destroy ozone
- evidence of decreasing ozone levels over Antarctica
- measurements in upper atmosphere showed high levels of compounds produced by breakdown of CFCs
What is ozone?
- form of oxygen with formula O3
- found in stratosphere
- absorbs UV light from sun and breaks it down to oxygen molecule and atom, O3+UV->O+O2
- the oxygen molecule and atom join together to make ozone again, O+O2->O3
How do chlorine free radicals from CFCs damage the ozone layer?
- UV light makes carbon-chlorine bonds in CFCs break down to form free radicals, CCl2F2->CClF2•+Cl•
- chlorine free radicals race with ozone turning it into oxygen and chlorine oxide, O3+Cl•->ClO•+O2
- chlorine oxide is very reactive and reacts with ozone to make 2 oxygen molecules and another free radical, ClO•+O3->2O2+Cl•
What are safer alternatives to CFCs?
- alkanes
- hydrofluorocarbons
What does hard water do?
- form lime scale inside pipes, kettles and boilers which can block pipes
- doesn’t lather easily with soap, makes scum instead
What is hard water caused by?
- calcium ions and magnesium ions
- as water flow as over rocks and through soils containing Ca2+ and Mg2+, they dissolve in it
- rainwater is slightly acidic and reacts with calcium carbonate to form calcium hydrogen carbonate
What is the overall equation for creating hard water?
Carbon dioxide+water+calcium carbonate -> calcium hydrogencarbonate
How can you remove temporary hardness from water?
- by boiling
- calcium hydrogencarbonate decomposes to form insoluble CaCO3
- calcium hydrogencarbonate-> calcium carbonate+water+carbon dioxide
How can you remove permanent hardness of water?
-adding washing soda, sodium carbonate
-carbonate ions join into calcium ions and make insoluble precipitate of calcium carbonate
>can also be removed by ion exchange resin
What is the method to compare hardness of water samples?
- add 100cm3 water to conical flask
- add 1cm3 soap solution and shake
- repeat till good lasting lather is formed
- record how much soap was needed
What is the general formula for an alcohol?
CnH2n+1OH
How is ethanol formed using fermentation?
Glucose->ethanol+carbon dioxide
C6H12O6->2C2H5OH+2CO2
How can ethanol be made by hydrating ethene?
- ethene reacts with steam to make ethanol
- needs temperature of 300 degrees and pressure of 70 atmospheres
- phosphoric aid catalyst is used
- C2H4+H2O->C2H5OH
Compare the fermentation and hydration methods of producing ethanol
Manufacture- fermentation is batch process and slow, hydration is continuous and fast but expensive
Sustainability-fermentation makes renewable fuel, hydration does not
Purity- fermentation isn’t very pure but hydration is
Atom economy- fermentation has lower atom economy
Percentage yield-hydration is better than fermentation
What type of emulsions are milk and butter?
Milk- oil-in-water emulsion, oil droplets are suspended in water meaning there’s less oil than water
Butter- water-in-oil emulsion, water droplets are suspended in oil meaning there’s more oil than water
How can vegetable oils produce biodiesel?
- rapeseed oil and soybean oil can be processed and turned into fuels
- vegetable oil provides a lot of energy
How are fats and oils used to make soaps?
- natural fats and oils are boiled up with sodium hydroxide which splits fats and oils to prove soap and glycerol
- this is called saponification
- fat+sodium hydroxide->soap+glycerol
Describe the saturated and unsaturated fats and oils
- saturated oils and fats only have single C-C bonds
- unsaturated oils and fats have at least one C=C double bond
- monounsaturated fats contain one C=C double bond
- polyunsaturated fats contain more than one C=C double bond
How can you test for an unsaturated or saturated fat?
- unsaturated fat will decolonize in bromine water, an addition reaction takes place at the double bond and a colourless dibromo compound is formed
- saturated fats don’t have double bonds so don’t react with bromine so it stays orange
How can you harden unsaturated oils?
- by reacting them with hydrogen in the presence of a nickel catalyst at about 60 degrees, this is called hydrogenation
- the hydrogen reacts with the double-bonded carbons and opens out the double bonds
Why are saturated fats worse for you than unsaturated fats?
-saturated fats increase the amount of cholesterol in blood which can block up arteries and increase the risk of heart disease
How do detergents work?
- they have a hydrophobic and hydrophilic part
- the hydrophilic end of the molecule forms strong intermolecular forces with water particles
- the hydrophobic part forms strong intermolecular forces with oil and fats
- when detergents come into contact with fat or oil a droplet of oil/fat forms surrounded by a coat of detergent
- this helps lift oily dirt out of fabric
How does dry cleaning work?
- there are weak intermolecular forces between solvent molecules and between the molecules of grease
- when solvent is applied to clothes, intermolecular forces are formed between solvent and grease molecules, so grease is surrounded
- when solvent is removed the grease is removed with it