Flashcards in C6 - Chemistry Out There Deck (78)
Write the half equations of the electrolysis of aluminium oxide and the electrode it takes place at.
2O2- - 4e- --> O2
Al2+ + 2e- --> Al
What is electrolysis?
The decomposition of a liquid by passing an electric current through it
What are the products formed during the electrolysis of aqueous sodium hydroxide (NaOH) and dilute sulfuric acid (H2SO4)?
Anode: hydroxide (water and oxygen bubbles form)
Write the half equations for the electrolysis of dilute sulfuric acid, containing H+, SO42- and OH- ions
2H+ + 2e- --> H2
4OH- - 2e --> OH-
What affects the rate of electrolysis?
The current and the time taken - each one is directly proportional to the amount of product made during electrolysis
What is the cation and the anion in the electrolysis of lead bromide? What's formed at each electrode? What are the half equations?
Cation: Pb2+ Anion: Br-
Lead formed at cathode, bromine formed at anode
Pb2+ + 2e- --> Pb
2Br- - 2e- --> Br2
In an electrolysis experiment using a current of 1.0A, 1g of copper was deposited in 60 minutes. 1) How long will it take to deposit 3g if the current is 2A? 2) What current needs to be used to deposit 10g of copper in 4 hours?
1) 1.5 hours
Describe the energy level diagram for an exothermic reaction (used in a hydrogen fuel cell).
The reactants have greater energy than the products - energy is given out to the environment during the reaction
Describe the energy level diagram for an endothermic reaction.
The reactants have less energy than the products - energy is taken in from the environment during the reaction
Describe how a hydrogen fuel cell works.
The fuel used is hydrogen and as it enters the cell at the anode. The hydrogen is forced through the catalyst and splits into two H+ ions and two electrons. The protons diffuse through the proton exchange membrane. The unused hydrogen leaves the cell before going through. The electrons can't diffuse through so go through the electric circuit and produce the current to power the cell. The hydrogen ions that diffuse through react with the oxygen that enters at the cathode to produce water, which is the waste product. A hot phosphoric acid catalyst is needed in this reaction.
What's the overall reaction in a hydrogen fuel cell?
2H2+O2 --> 2H2O
What are the half equations that take place in hydrogen fuel cell?
Anode: H2 - 2e- --> H+ 2H2O
What are the advantages of fuel cells in space?
1. They're lightweight
2. The water (waste product) can be drunk by the men on a manned spacecraft
3. They're compact
4. They have no moving parts
Compare the use of fuel cells to hydrocarbon fuels (diesel, petrol).
1. Fuel cells don't release harmful waste products (such as CO2), so don't contribute to global warming and the greenhouse gases
2. There's a large potential source of hydrogen - the water can be decomposed by electrolysis to produce even more hydrogen
3. The stages in producing a fuel cell are more efficient than conventional fuels - electrical energy transferred directly when required
4. The catalyst in hydrogen fuel cells are often poisonous
5. Most of the world's hydrogen production is done using fossil fuels (reacting steam with coal or natural gas) - this produces CO2 emissions
Explain a thermite reaction.
A vigorous exothermic reaction between aluminium and iron (III) oxide that produces aluminium oxide and iron.
The iron (III) oxide loses oxygen, so is reduced to iron - this melts. The aluminium gains oxygen, so is oxidised to aluminium oxide.
2Al2 + Fe3O3 --> Al2O3 + 3Fe
What is a reducing and oxidising agent?
Reducing Agent - substance that causes the other to be reduced (gain electrons/lose oxygen)
Oxidising Agent - substance that causes the other to be oxidised (lose electrons/gain oxygen)
What is the order of reactivity (most to least reactive) of the 5 common metals?
A reaction takes place between Iron(III) Nitrate and Magnesium. What is the overall reaction and the half equations? What are the reducing and oxidising agents?
Fe(NO3)3 + Mg --> Fe + Mg(NO3)2
Fe3+ + 3e- --> Fe - reduced
Mg - 2e- --> Mg2+ - oxidised
Specator ions = NO3-
The reducing agent is Magnesium and the oxidising agent is Iron.
What two things does rusting require?
Oxygen and water
What is the equation for rusting? What happens to the iron and the oxygen?
iron + oxygen + water --> hydrated iron (III) oxide
The iron is oxidised to form Fe3+ ions, and the oxygen is reduced to form oxide (O2-) ions
What are the methods of preventing rust?
1. Coat with a layer of paint
2. Coat with a layer of oil or grease
3. Galvanising - add a layer of zinc
4. Using alloys of the iron - adding carbon or chromium
What is sacrificial protection?
A layer of either zinc or tin is added to the iron. This ensures that when the material is exposed to air and water, the air and water reacts with the layer instead of the iron. Therefore, the zinc or tin is rusted instead of the iron - thus sacrificing itself. However, if the tin layer is scratched and the iron exposed, the iron will rust faster as iron is more reactive than tin. If zinc is used then the iron won't be reacted with regardless, as zinc is more reactive than iron and is reacted with in preference.
What are some uses of ethanol?
1. Common drinking alcohol
3. Solvent in perfumes and aftershaves
What does it mean if a substance is organic?
It contains carbon, excluding CO2 and carbonate substances
Explain the fermentation reaction and what's needed.
Yeast are needed as they contain enzymes to convert glucose to CO2 and ethanol - oxygen can't be present because yeast anaerobically respire.
C6H12O6 --> CO2 + C2H5OH
A warmer place is optimal as the enzymes have more energy to work. Limewater is used in experiment at school to prove CO2 is made and act as an airlock so oxygen can't get back in once it's out.
The ethanol eventually kills the yeast so it sinks to the bottom, and the ethanol is purified using fractional distillation.
Explain the purification of ethanol.
The ethanol is extracted from the yeast to increase the purity of ethanol. Heat is applied to the ethanol-water mixture. A fractionating column is on top of the ethanol-water mixture, which helps the ethanol vapour separate out when heated. The vapour is condensed in a condenser to become purified ethanol liquid
What's the equation that take places in a hydration reaction?
ethene + steam --> ethanol
C2H4 + H20 --> C2H5OH
What's needed in a hydration reaction?
Temperature of 300C
A hot phosphoric acid catalyst
Compare the fermentation and hydration reaction.
1. Fermentation is more sustainable because it uses a natural renewable resource (yeast), unlike Hydration that uses a non-renewable crude oil (ethene)
2. Hydration is more expensive than Fermentation because of the conditions needed - high temp, catalyst
3. The atom economy and percentage yield of Hydration is 100%, Fermentation is 51% atom economy and 15% percentage yield
4. Fermentation produces a low-purity product, Hydration produces a high-purity product - no waste`