Thanks all!
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a friend done the homework for me:
2c-b: C10H14BrNO2
(RMM(2c-b)+RMM(HCl)/RMM(2c-b)+RMM(HBr))*10mg
RMM(2c-b)=10*12,01+14+79,9+14+2*15,99=120.1+14+79.9+14+31.98=259.98
RMM(HCl)=1+35.45=36.45
RMM(HBR)=1+79.99=80.99
RMM(2c-b.HCl)=296.43
/RMM(2c-b.HBr)=340.97
=0.869
*10
=8.69
10 mg. 2c-b.HBr = 8.69 mg 2c-b.HCl.
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