Edexcel Chemistry Topic 5 (Quantitative analysis (The atom economy is the…
Edexcel Chemistry Topic 5
Transition metals, corrosion and alloys
Most metals are transition metals as they are located in the middle of the periodic table.
They are relatively hard, shiny , strong and malleable materials that can conduct heat and electricity.
They from coloured compounds and have high densities and high boiling points.
Compounds containing Fe3+ are normally orange/brown and ones with Fe2+ ions are normally light green.
Transition metals are often used as catalysts like iron (Haber process) or vanadium pentoxide (contact process).
Metals corrode in the presence of water and oxygen to form their metal oxides. Corrosion is caused by redox reactions where the metal is oxidised and the oxygen is reduced.
Rusting is the corrosion of iron and only happens where iron is in the presence of oxygen from the air
How to prevent rusting:
Exclusion of water- using a barrier such as painting. Also oiling or greasing for objects that have moving parts.
Exclusion of oxygen- using a barrier such a painting. Also oiling or greasing for objects that have moving parts.
Sacrificial protection- this is the method of attaching more reactive metals to the object. This works because as the metal is more reactive than the metal of the object, it oxidises (gives up its electrons easier) and thus corrodes rather than the object. This works until the sacrificial metal corrodes away.
Electroplating is the coating of the surface of a metal with anther metal using electrolysis. The cathode is the object you're going to electroplate and the anode is a bar of the metal you're using for the plating. Your electrolyte should be a solution containing metal ions of the metal being used to plate.
Electroplating is used to stop objects from corroding, it is done with extremely unreactive metals. Household kitchen items are often electroplated like cutlery.
Jewellery and decorative items are often electroplated with metals like silver or gold which improves their appearance, it makes them shiny and attractive.
Making metals into alloys often increases the strength of the substance as in pure metals, the atoms can slide over each other as metals are usually malleable. When you add atoms of a different size, it changes the structure and it makes it hard or impossible for the atoms to move over the new atoms. This increases the strength.
Iron is often alloyed with other metals or substances like carbon and nickel (makes steel) because it increases its strength and makes it more useful. The more carbon is added to iron, the stronger it becomes however, when you add too much; it becomes brittle.
Gold is used in jewellery because it is extremely unreactive and doesn't corrode. It can also be used as currency because it is rare and holds its value.
Copper is used in pipes and wires because it is a good conductor and is resistant to corrosion and doesn't react with water.
Aluminium is used in foil because it is extremely malleable. It is also used in bike frames because it has a very low density.
Magnalium is 95% aluminium and 5% magnesium and it is an engineering alloy used for aircraft parts and scientific instruments. Magnalium is less dense and almost 4 times stronger than aluminium. Although it is denser than magnesium, it is almost two times stronger than it. These allow for the production of strong and lightweight metal parts.
Brass is used in the making of instruments as it is mainly copper and is resistant to corrosion. Copper is a better electrical conductor but brass is stronger which makes it more suitable to make electrical pins.
Cm^3 to dm^3 means you should divide it by 1000.
In order to convert between concentrations in mol dm^-3 and g dm^-3 multiply it by the relative formula mass of the solute.
Percentage yield is the % of actual yield formed from the theoretical yield. The theoretical yield is the mass of product you'd get if
the reactants were converted into product.
The equation for percentage yield is:
(actual yield/ percentage yield) x100
Percentage yield will always be from 0% to 100%- it's important in industry to have reactions that have a high percentage yield so not a lot of reactant is wasted.
There will never be 100% yield because of:
Incomplete reactions- not all of the reactants are converted to product which will result in a lower yield achieved than expected.
Practical losses- there is always loss of reactants when transferring chemicals between containers.
Unwanted reactions- if unexpected reactions happen, the yield of the intended product goes down. These can be caused by impurities in the reactants or sometimes by changes to reaction conditions.
The atom economy is the amount of reactant which is converted into the desired product when manufacturing a chemical. 100% atom economy means that
the atoms in the reactants have been turned into useful products. The higher atom economy, the 'greener' the process.
The equation for atom economy is:
(total Mr of desired products / Total Mr of all products) x 100
Reactions with low atom economies are not sustainable or profitable since they use up materials very quickly and this makes the raw materials expensive. There is usually more than one way to make a product though so the way that atom economy can be increased is finding the reaction will produce useful 'by-products' rather than useless ones.
In industry multiple things need to be considered:
the percentage yield
the rate of reaction
the equilibrium position if applicable
The volume occupied by one mole of any gas at room pressure and temperature is 24 dm^3 or 24000 cm^3
The volume occupied by one mole of gas is known as the molar volume and it usually has the units of dm^-3 mol^-1 (dm^3 per mole). The equation for molar volume is:
gas volume/number of moles
You can use Avogadro's law in molar volume calculations because each gas at RTP have the same molar volume so the balanced symbol equation will show how much gas will be produced or used up.
A fuel cell is an electrical cell that uses fuel and oxygen and uses energy supplied by the reaction between them to produce voltage efficiently.
Chemical cells produce a voltage across the cell until one of the reactants is used up.
The reaction between hydrogen and oxygen produces energy, this is what happens in a hydrogen-oxygen fuel cell. They produce voltage without the pollutants, only nice clean water.
The equation is: 2H2 + O2 = 2H2O.
Positives and negatives of Fuel cells:
More efficient than power stations or batteries at producing electricity. If the heat produced is used also, their efficiency can be over 80%.
In a fuel cell, electricity is generated directly from the reaction and thus there are less stages for energy to be lost as heat. And unlike a car engine or a fossil fuel burning power station, there are no moving parts so no energy is lost through friction.
Fuel cells don't produce pollutants like greenhouse gases etc and the only products are water and heat which would be an advantage in cities where air pollution is a big problem.
This could also replace batteries which are incredibly polluting to dispose of as they are made of highly toxic metal compounds.
Hydrogen is a gas and takes up more space than liquids like petrol.
It's very explosive and flammable so it is dangerous to store and difficult to store safely.
The hydrogen gas is usually made from the electrolysis of water or from hydrocarbons. Electrolysis takes electricity which will likely be generated by the burning of fossil fuels. Therefore, it is not as renewable as originally thought.
The Haber process is the reversible process between nitrogen and hydrogen to form ammonia.
The rate of attainment of equilibrium is much quicker using high temperatures, high pressure, high concentrations. However these conditions could decrease the yield depending on the reaction. Rate of attainment of equilibrium is always quicker when using a catalyst, a catalyst will never decrease atom economy or percentage yield.
The conditions in industrial processes are always a compromise. The cost of the extraction of the raw materials for an industrial process will affect the economic viability of the process- if they're too expensive then it may not be profitable to make the product.
Energy costs of reaching and maintaining the conditions of a reaction also affect whether something is profitable; high pressures and temperatures are expensive so lower temperatures and pressures are maintained where possible. It is also vital to an industrial process that the conditions maximse the yield but also keep the reaction running at an acceptable rate.
The conditions of the Haber process are a compromise because higher pressures favour the forward direction so pressures are as high as possible to give the best yield but without being too expensive to maintain- 200 atm.
The forward direction of the Haber Process is exothermic so a higher temperature would favour the wrong direction and decrease the yield so the temperature should be as low as possible. However, lower temperatures mean a lower rate of reaction which isn't sustainable for an industrial process so the operating temperature is 450 degrees. This is a compromise between maximum yield and speed of reaction.
The main elements in fertilisers are phosphorus, nitrogen and potassium- plants absorb these nutrients from the soil. If plants don't get enough of these elements then their growth and life processes are affected.
They help plants to grow faster and bigger.
Ammonia fertilisers can have the chemicals in them controlled and are also soluble so they can sink down into the soil to reach the plants.
Ammonia can be reacted with oxygen and water in a series of reactions to make nitric acid. Ammonia can be reacted with nitric acid to form the salt ammonia nitrate which is used as a fertiliser.
How to make ammonia sulfate in a lab:
Set up a titration apparatus then add a few drops of methyl orange to the ammonia which will make it turn yellow.
Slowly add the sulfuric acid drop by drop to the ammonia till it
turns red while gently swirling the flask.
This ammonia sulfate isn't pure as it has methyl orange in it so note the exact amount of sulfuric acid to neutralise the ammonia and repeat without the indicator.
Evaporate the solution gently then leave to crystalise. Then filter to get pure ammonia sulfate crystals.
How to make ammonia sulfate in industry:
Ammonia and sulfuric acid are made from their raw materials first from the Haber Process and the Contact Process.
A large chamber is filled with ammonia gas. Sulfuric acid is sprayed into the reaction chamber where it reacts with the ammonia to form ammonia sulfate powder.