Question

the rock dolomite is a double carbonate of magnesium and calcium CaCO3.MgCO3
when heated strongly a product calcined dolomite is formed which is used to line some furnaces for the production of metals
why is calcined dolomite used for this purpose?
1. it is a refractory material
2.it wil absorb acidic impurities in metallurgical processes
3.reduce metalic oxides to metals

if somebody could help me tell which options are correct.. they could be more than one... and why??

Answer 1

There should be a preliminary thought (PT) before considering the statements.

PT: The question is from Group II elements and involves heating of carbonate. So, it has to deal with thermal decomposition of carbonates and the product formed after decomposition: CaCO3 >>>heat>>> CaO + CO2

MGCO3 >>> hear >> MgO + CO2
Most probably, the calcinated dolomite will contain the mixture of MGO and CaO as CO2 will escape being gas.

Statement 1: This can be tackled in two ways




Simple case: (Useful for AS students) : The question itself has the answer. Read the line '....which is used to line some furnaces....'. You can be sure that statement 1 is correct unless your vocabulary prevents you from understanding the word 'refractory'

Case II: (For A2 students only). You have read that MgO has high exothermic lattice enthalphy, which means that large heat input is required to break its strong lattice. Hence, it is thermally stable or it has large melting point. So, it can relatively withstand high temperature and is ideal for its use in refractory lining of furnaces.

Now, we know st. 1 is correct. We now can eliminate choice C

Statement 2: CaO and MgO both are basic oxides so will react to acidic impurities. St. 2 correct so eliminate choice D.

Statement 3: (This is my personal logic, I mean 'guess'. If anyone can come up with better explanation, you are welcome)

The cations present are Ca2+ and Mg2+. To reduce others these cations must get oxidised. I have not seen cations like Ca3+ or Ca4+, so I assume that these cations cannot be oxidised. After all, they are not transistion elements to show variable oxidation states. Statement 3, by my guess, is incorrect.

So I think the correct answer is B.
My logic for statement 3 worked. The mark scheme says B is the correct answer.

Answer 2

yes i have already seen the marking scheme just wanted to knw the explanation. thnku for the help

Answer 3

i got it without all this logic! :P

Answer 4

you gotta know that it cant reduce! and it can absorb impurities coz it has calcium like in o levels we studied that calcium silicate is formed in Extraction of iron.

and it is stable at high temperatures because if something formed from decomposition of a product it is always stable and examiner gave us a hint * used to line furnaces*

KISS

Keep it short and Simple lol

Answer 5

amazing