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    I stronly believe there is an error in this Q.

    1.05 l at STP = 1.04/22.4 = 0.0464 moles of NO2 gas.

    As there are one mole each of Cu AND of NO2 in 1st reaction,
    therefore the no of moles of copper was also 0.0464.

    No of grams of copper in original brass = 0.0464 X 63.5 = 2.95g

    This implies that there was more copper in the brass than the weight of the brass itself (IMPOSSwhich isIBLE!).

    I think the examiner has mixed up his/her numerator with denominator
    i.e. he/she has done 2/2.95 instead of 2.95/2 to work out original mass of copper (I bet this Q is from Edexcel paper!)

    The answer was probs (a) which is roughly 2/2.95.

    UTTERLY SHAMEFUL of the examiner (unless I am making a blunder which is possible. of course!

    M
 
 
 
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