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Qualification => Subject Doubts => GCE AS & A2 Level => Sciences => Topic started by: ashwinkandel on October 05, 2010, 05:48:52 pm

Title: Chemistry numerical
Post by: ashwinkandel on October 05, 2010, 05:48:52 pm

What mass of solid residue can be obtained from the thermal decomposition of 4.10 g of
anhydrous calcium nitrate?
A 0.70 g B 1.00 g C 1.40 g D 2.25 g

my friend asked me this question. i said D but he said C is the answer given in marking scheme. Can someone tell me why and how?

Title: Re: Chemistry numerical
Post by: Deadly_king on October 05, 2010, 05:56:32 pm

Quote from: ashwinkandel on October 05, 2010, 05:48:52 pm

What mass of solid residue can be obtained from the thermal decomposition of 4.10 g of
anhydrous calcium nitrate?
A 0.70 g B 1.00 g C 1.40 g D 2.25 g

my friend asked me this question. i said D but he said C is the answer given in marking scheme. Can someone tell me why and how?

I guess I already answered that  ;)

Anyway here it is once more :
First you need to write the equation of the decomposition of the nitrate which will be :
Ca(NO₃)₂ ---> CaO + NO₂
NO₂ will escape as it is a gas. Residue will consist of CaO only.

Mr Of Ca(NO₃)₂ = 164.1
Mr of CaO = 56.1
From equation :
1 mole of Calcium nitrate produces one mole pf CaO
Hence 164.1g of Ca(NO₃)₂ produces 56.1g of CaO
Therefore 4.1g of Ca(NO₃)₂ will produce (56.1/164.1)*4.1 = 1.40g

Hence answer is C

Title: Re: Chemistry numerical
Post by: ashwinkandel on October 05, 2010, 05:58:15 pm

thanks deadly_king +rep

Title: Re: Chemistry numerical
Post by: Deadly_king on October 05, 2010, 06:07:27 pm

Quote from: ashwinkandel on October 05, 2010, 05:58:15 pm

thanks deadly_king +rep

Anytime dude :)