Btw I'm going to steal this thread. How do you do the MC question 20 in 2010? I know it's pathetic to struggle at MC, but I can't do it!
Lol it's quite simple to start a new thread but anyway.
As the curve will be linear or close to it, we can say
which equals 12.5 mg/L
therefore Cu2+ in 100 mL is 1/10x12.5=1.25 mg
number of moles of Cu2+= 0.00125/65.55 = 1.97x10^-5 moles
therefore number of moles of Cu2+ = number of moles of CuCO3
number of moles of CuCO3 = 1.97x10^-5
therefore mass of CuCO3 = 1.97x10^-5 x 123.55 = 2.43x10^-3g
therefore answer is (B), oh and don't worry multiply choice is hard so it's not pathetic