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Biology; Chemistry; Physics: Post your doubts here!

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I need to focus on Organic pretty badly, that's the only part where i am losing marks :(

heyy guys for chem is aluminium extraction (all with the cryolite stuff) is it included in the syllabus for 2012? if yes then plz give me some notes on it if u have any thanks :)

Yes it is ..

proof from 12 syllabus:
wS0n.jpg



Aluminum is the most abundant metal to be found in the earth's crust. However, it is uneconomical to extract it from most rocks and clays, and instead, it is extracted from an ore called bauxite.

The ore is usually found near the surface in layers between 4 and 12 metres thick. It is mined by open-cast mining, which is relatively cheap.

Most bauxite ores contain between 25-30% aluminum oxide with impurities of sand and iron oxide. The impurities make the ore reddish-brown in colour. The two largest producers of bauxite are Australia and Jamaica. Once mined, it is then purified by dissolving it in sodium hydroxide. the impurities do not dissolve and are filtered off. The dissolved aluminium oxide is then precipitated out as aluminum hydroxide by diluting with water. This is then heated to form pure white aluminum oxide, or alumina. The aluminium is then extracted by electrolysis.

To conduct electricity, the aluminum oxide must be molten. However, it has a high melting point (Over 2000C), so another aluminum compound called cryolite (Na3AlF6) is added. This lowers the melting point. During electrolysis, the aluminum ions migrate towards the graphite cathode, where molten aluminum collects and is siphoned out.

Cathode : Al3+(l) + 3e- ---> Al(l)

Anode: 2O2-(l) -----> O2(g) + 4e-

It requires 15 kilowatt-hours of electricity to produce 1 kilogram of aluminum.
 
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Can anyone please answer this....explain why aluminium is extracted by electrolysis whereas iron is not
 
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Can anyone please answer this....explain why aluminium is extracted by electrolysis whereas iron is not

Iron can be reduced by heating with carbon which is a lot cheaper than doing an electrolysis of Iron that's the reason why iron is not extracted using electrolysis, Since aluminum cannot be extracted by heating with carbon (carbon is below in the reactivity series) the only method to extract aluminum is Electrolysis.
 
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Hw did u get it ..??

First get the number of moles for U02 .. Mr of U02= 270g .. 1 tonnes = 1million g

Moles of U02=1million/270 = 3703.

1 Mole of U02 produces 1 mole of U .. check the equations .. that's how i got it.

therefore 3703 produces 3703.

Mass of U= Moles*Mr
= 3703*238
= 881,481 grams (divide it by 1 million to get the answer in tonnes)
 
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First get the number of moles for U02 .. Mr of U02= 270g .. 1 tonnes = 1million g

Moles of U02=1million/270 = 3703.

1 Mole of U02 produces 1 mole of U .. check the equations .. that's how i got it.

therefore 3703 produces 3703.

Mass of U= Moles*Mr
= 3703*238
= 881,481 grams (divide it by 1 million to get the answer in tonnes)
thats correct,approximately.
 
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Hw did u get it ..??
U have the equation of step 1 it shows that 1 mol of UO2 gives 1 mole of UF4 so calculate the mass of 1 mol of U02 mr is 270 multiply it with 1 so 1 mole is 270 g now notice in step 2 1 mole of UF4 gives 1 mol of uranium that means 270g of UO2 gives 238g of uranium now 1 tonne has 1milliong calculate the number of moles of 1 tonne of UO2 they come 3704 as ratio is 1:1 calculate the mass of 3704 of u it comes as 881552g now divide this by 1 million ans is 0.88
 
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