Topic 5 - separate chemistry 1 Flashcards
What are the typical properties of transition metals?
High melting point
High density
Form coloured compounds
Can be used as catalysts
Which transition metal is used as a catalyst in the Haber process?
Iron
What causes metals to corrode?
Oxygen reacts with the metal to form a metal oxide
Why is corrosion of a metal a redox reaction?
The metal loses electrons so is oxidised and the oxygen gains electrons so is reduced.
What is rusting?
The name specifically given to the corrosion of iron when it reacts to oxygen and water in the air
What two substances nwe’d to be excluded to prevent rusting?
Oxygen and water
How can oxygen and water be excluded to prevent iron rusting?
Paint the metal
Coat the metal in oil/grease
Cover the metal in plastic
Keep the metal in a vacuum container
What is sacrificial protection? How does it prevent corrosion?
When the metal being protected from rusting is galvanised with a more reactive metal.
The outer metal will corrode first and will prevent the corrosion of the inner metal.
Which metal is used in the sacrificial protection of iron?
Zinc
What is electroplating?
A process in which a metal is coated with a layer of another metal
What are two reasons for using electroplating?
To make a metal more resistant to corrosion
To improve the appearance of a metal
Explain how electroplating works
The metal being coated is the cathode. The metal that will form the exterior layer is the anode. The electrolyte solution must contain ions of the metal which will form the outer coating. A power supply is connected to both electrodes
Why are pure metals generally very malleable?
The atoms lie in uniform rows which are able to slide over one another
What is an alloy?
A mixture of two or more metals or a metal and another element
A pure metal can be converted into an alloy. How does this increase the strength of the product.
Allows contain several metals which will have different sized atoms. This distorts the regular arrangement of the atoms so the layers are unable to slide over one another very easily
Why is iron alloyed with other metals to produce alloy steels?
Iron is quite brittle so it is combined with other elements such as carbon which produces a metal with more desirable qualities
What are the desirable qualities of low carbon steel, high carbon steel and stainless steel?
LCS: Malleable so used for sheeting
HCS: hard so used for cutting tools
SS: Corrosion resistant so used for cutlery
What property of copper makes it suitable to be used in electrical cables?
It is a very good electrical conductor
What property of aluminium makes it suitable for use in aircrafts?
It has a low density
What is a key property of gold that makes it suitable for use in jewellery?
It is very unreactive so resistant to corrosion
Jewellery appearance will not be affected over time
What is magnalium?
An alloy of magnesium and aluminium
What are the desirable qualities of magnalium?
It is lighter and stronger than aluminium and more resistant to corrosion
What is magnalium used for?
Cars and aircrafts
What is brass?
An alloy of copper and zinc
What are desirable qualities of brass?
It is hard and resistant to corrosion
What is brass used for?
Decorative hardware such as plumbing fittings
How do you calculate the concentration of a solution in mol dm-3?
Concentration (mol dm-3) = moles /volume (dm3)
How can you convert concentration in g dm-3 to mol dm-3?
Concentration (mol dm-3) = concentration (g dm-3)/ molecular mass
Describe how to carry out and acid-alkali titration to find the concentration of alkali
- Rinse the Pipette with the solution of unknown concentration (alkali). Use this Pipette to add a known volume of alkali to a conical flask
- Add a few drops of indicator
- Rinse and fill the Barette with acid
- Gradually add the acid to the conical flask
- Record the volume in the Barette when the indicator changes colour
- Repeat the experiment until you have concordant results
- Use results to calculate a mean titre and the concentration of alkali
If you know the volume of acid required to neutralise an alkali, how could you calculate the concentration of the acid given the alkali concentration and volume?
Calculate the number of moles of the alkali using the known volume and concentration (moles=concentration x volume)
Use the chemical equation to work out how many mole of acid and alkali that react and hence work out how many mole of acid have reacted
Divide the moles of acid by the volume used in neutralisation to find concentration
What is meant by the term theoretical yield?
The amount of product that would be collected under perfect reaction conditions
How do you calculate percentage yield?
Percentage yield = (actual yield/theoretical yield) x 100
Why could the actual yield of product be less than expected?
Incomplete reaction
Competing, unwanted side reactions
Practical losses, for example some solid may get lost when being transferred between beakers
What is the atom economy of a reaction?
A measure of the efficiency of the reaction. It looks at the amount of reactants that get turned into useful products
How can atom economy be calculated?
(Molecular mass of desired product/molecular mass of all products) x 100
Why might one reaction pathway be chosen over another?
Higher atom economy Higher yield Faster rate By-products are more useful/less harmful Equilibrium position favours products more
What does avogadro’s law state about gas volumes?
At the same temperature and pressure, equal amounts of gas will occupy the same volume
What is the molar volume of a gas?
The volume occupied by one mole of molecules of any gas at room temperature and pressure
What is RTP?
Room temperature and pressure:
20°C
1 atmosphere
How can the molar volume of a gas be calculated?
Molar volume = volume (dm3)/moles of gas
What are the units of molar volume of a gas?
Dm3mol-1
What is the Haber process?
A reversible reaction that forms ammonia from nitrogen and hydrogen
Describe the steps that are carried out during the Haber process
- Reactants are obtained (hydrogen from natural gas, nitrogen from air)
- The gases are compressed to 200atm and heated to 450°C before being pumped into a tank containing layers of catalytic iron beads
- Ammonia forms
- Ammonia and unreacted hydrogen and nitrogen pass into a cooling tank where the ammonia is collected as a liquid
- The unreacted hydrogen and nitrogen are then recycled back into the tank
What is meant by the term dynamic equilibrium?
The rate of the forward reaction equals the rate of the backwards reaction. The concentration of reactants and products are constant.
What is the chemical equation for the formation of Ammonia from hydrogen and nitrogen?
N2 + 3H2 = 2NH3
What are the ideal conditions for the Haber process?
450°C temperature
200 atm pressure
Iron catalyst
How is the rate of attainment of equilibrium affected by temperature?
A higher temperature means equilibrium is reached quicker. This is because the reacting particles have more kinetic energy so there are more frequent successful collisions
How is the rate of attainment of equilibrium affected by a catalyst?
Equilibrium is reached faster when a catalyst is used because the catalyst provides an alternative reaction pathway with a lower activation energy
How is the rate of attainment of equilibrium affected by pressure?
It is reached faster with a higher pressure. This is because there are more particles in the same volume (or the same number of particles in a smaller volume) so more collisions between reacting particles)
How is the rate of equilibrium affected by concentration?
It is reached faster at a higher concentration. This is because there are more particles in the same volume so more collisions between the reacting particles
Why are the conditions used in the Haber process a compromise?
A high temperature increases the rate of reaction however, it will favour the reverse reaction, decreasing the yield. A compromise of 450°C is used to obtain a sufficient rate and yield.
A high pressure speeds up the rate and favours the forward reaction (increasing the yield). High pressures can be dangerous and require expensive machinery so a compromise of 200atm is used
Why is a catalyst used in the Haber process?
To increase the rate of reaction so more product is produced within the same time frame
What factors should be considered before deciding the conditions for an industrial reaction?
Availability and cost of raw materials
Energy requirements
Optimum temperature and pressure for high yield and fast rate of reaction
Need for a catalyst
What is the purpose of fertilisers?
To promote plant growth
What chemical compounds might fertilisers contain?
Nitrogen, phosphorus and potassium compounds
What compounds are found in NPK fertilisers?
A combination of all three fettiliser compounds : nitrogen, phosphorus and potassium compounds
Which parts of plant growth do the compounds nitrogen, potassium and phosphorus help with?
Nitrogen: healthy leaves
Phosphorus: healthy roots
Potassium: growth and healthy fruit/flowers
Which ammonium salt is most commonly used in fertilisers?
Ammonium nitrate
How is the salt ammonium nitrate formed?
React ammonia with nitric acid
Write the chemical equation for the formation of ammonium nitrate
NH3 + HNO3 -> NH4NO3
What is the chemical equation for the formation of ammonium sulphate from ammonia and sulphuric acid?
2NH3 + H2SO4 -> (NH4)2SO4
How can ammonium sulphate be produced on an industrial scale?
Raw materials obtained from the Haber process (ammonia) and the contact process (sulphuric acid). A large reactor chamber is filled with ammonia gas. Sulphuric acid is sprayed into the chamber from above. Ammonium sulphate Crystals are produced
What are the advantages of the laboratory method of producing ammonium sulphate?
Faster rate of reaction
Small reactant quantities can be easily bought
Room temperature and pressure easily controlled
Simple equipment required
What is the disadvantage of the laboratory method of producing ammonium sulphate?
There is a very small yield
What are the advantages of the industrial process of producing ammonium sulphate?
A continuous process so a continuous yield
Large volumes of product
What are the disadvantages of the industrial process of producing ammonium sulphate?
Very expensive and complex
Slow rate of reaction
High energy requirement
Other industrial processes required to obtain the reactants
How is a voltage produced from a chemical cell?
Two metals of different reactivities are placed in an electrolyte.
The more reactive metal releases electrons, becoming positively charged. The electrons flow to the other electrode which becomes negatively charged. The difference in the ability of each electrode to release electrons causes a voltage to be produced
When will a chemical cell stop producing a voltage?
When one of the reactants has been used up
What is a fuel cell?
A cell that continually produces a voltage as long as it is supplied with oxygen and a fuel (like hydrogen)
What is the only product of a hydrogen-oxygen fuel cell?
Water
How does a hydrogen-oxygen fuel cell work?
Hydrogen and oxygen are pumped through porous electrodes. The electrolyte is often an acid such as phosphoric acid
Hydrogen and oxygen react, producing electricity and water
Write an equation for the overall reaction that takes place in a hydrogen-oxygen fuel cell
2H2 + O2 -> 2H2O
What are the advantages of using fuel cells?
No pollution produced
Produce more energy than an alternative fuel like petrol
Continuous process as long as fuel is supplied
What are the disadvantages of using fuel cells?
Material used to make them are expensive
High pressure tanks required to store oxygen and fuels like hydrogen
Hydrogen is expensive and hard to store
Efficiency is affected by temperature
