Flashcards in 2.7 Extraction of metals Deck (20)
Before reduction, how are sulfide ores converted into oxides?
By roasting, this is just heating them in air
What has to be removed from an ore to obtain a pure metal?
Oxygen or sulfur
Are metals reduced or oxidized in their extraction?
Why can't reactive metals be reduced by coke?
The temperature required for the reaction is too high and so uneconomic. Also they react with carbon to form carbides.
In iron reduction by carbon, what substances are added into the blast furnace?
A mixture of iron ore, coke and limestone
What happens at the base of the furnace?
Coke burns in the blast of hot air (this is an exothermic process and this generates more heat so that the temperature is around 2000k). CO2 is formed which then reacts with more coke to form CO.
What is the reducing agent in the reduction of iron?
Carbon monoxide, formed when the coke burns in air which forms CO2 which reacts with coke again to make CO. CO reacts with iron oxide to produce molten iron: Fe2O3(s) + 3CO(g) --> 2Fe(l) + 3CO2(g)
How can copper mining waste be turned into pure copper?
By spraying the waste with dilute acid in the presence of a bacterium. The bacterium will work on the low grade ores remaining in the copper mining waste leaving copper ions. The copper is extracted from the solution by reduction with scrap iron: Cu2+(aq) + Fe (s) --> Cu(s) + Fe2+(aq)
Aluminium reduction by electrolysis- Before electrolysis, the aluminium oxide must be in molten or in solution, what is the solvent and what temperature does this solution melt at?
The oxide is dissolved in molten cryolite (Na3AlF6) and it melts at 1240k.
Aluminium- electrolysis reduction- After the solution is made and put in the electrolysis cell what are the products at each electrode and what are the half equations? Also what is the full equation when the half equations are added together?
At the cathode, aluminium is formed: 2Al3+ + 6e- --> 2Al
At the anode, oxygen is formed: 3O2- --> 1.5O2 + 6e-
The overall process is the decomposition of Al2O3 and the equation is: Al2O3 --> 2Al + 1.5O2 (the electrons cancel out)
Aluminium reduction- why do the anodes frequently need replacing in the reduction of aluminium?
The process runs continuously so the oxygen formed at the anode burns the carbon anode away and so it needs to be replaced quite often
Why can't titanium oxide be reduced with carbon?
Titanium carbide is formed which makes the metal brittle
What are the conditions for converting rutile (TiO2) to titanium chloride?
1173k, with coke and chlorine. The equation for the reaction is:
TiO2(s) + 2C(s) + 2Cl2(g) --> TiCl4(l) + 2CO(g)
In the 2nd stage of extracting titanium, titanium chloride is reduced. What is it reduced by and what are the conditions?
Molten sodium under an inert argon atmosphere at 1300k. (inert argon atmosphere so metals don't react with N2 or O2 from the air)
The reaction for this is: TiCl4(l) + 4Na(l) --> Ti(l) + 4NaCl(l)
Why is the reduction process of titanium not very efficient?
It is a batch process
Like titanium, tungsten cannot be reduced by carbon as a carbide forms, so how is tungsten extracted from its oxide ore?
By reduction with hydrogen at high temperature:
WO3 + 3H2 --> W + 3H2O
Why is the reduction of tungsten dangerous?
Hydrogen is a flammable gas
Metal can be recycled by melting it down and reforming it, what is an advantage of this?
-reduces amount of metal that goes to landfill
-less metal needs to be extracted from their ores which is expensive and harms the environment
-recycling does not produce CO2
What is a disadvantage of recycling metal?
-there are energy costs for melting metal and CO2 is made in the production of this energy
-energy is also required in the sorting and transporting of the recycled metals