IIT JEE , AIEEE Forum - Chemistry , Physical Chemistry

kirtana

hiii
plz answer this...
A granulated sample of aircraft alloy(al, mg , cu) weighing 8.12 g was first treated with alkali and then with very dilute HCl, leaving the a Residue. The residue after alkali boiling weighed 2.10g and the acid insoluble residue weighed 0.69g. what is trhe composition of the alloy????

deepak_agarwal

hii

the main problem in the question is to find out the reactions taking place.

the reactions taking place are

2Al + 2NaOH

2NaAlO₂+3H₂

Mg+2HCl

MgCl₂+H₂

Cu+HCl

no reaction

remember these three points:

only Al reacts with NaOH

only Mg reacts with HCl

Cu reacts with none

let Al be a grams,Mg be b gms and Cu be c grams in the alloy

a+b+c=8.72

b+c=2.10 (because Mg and Cu do not react with alkali)

c=0.69 (because Cu reacts with none)

solve to get a=6.62 g

b=1.41 g

now find the percentages and u r done.

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