2010 Chemistry qn20 mc (1 Viewer)

forthehsc · Oct 31, 2011

can someone explain how we're meant to do qn20, i dont really undertsand ppm

b3kh1t · Nov 1, 2011

forthehsc said:
can someone explain how we're meant to do qn20, i dont really undertsand ppm

ppm is basically the same as mg/L, where 1000 mg = 1 g. If you want to another example look here http://community.boredofstudies.org/showthread.php?t=270087, and if you still need help just say

the answer to the question is as follows.

As the curve will be linear or close to it, we can say $\frac{[Cu^{2+}]}{0.500}=\frac{10ppm}{0.400}$
$\therefore Cu^{2+}=12.5ppm$ which equals 12.5 mg/L

the amount of Cu2+ in 100 mL is 1/10x12.5=1.25 mg
therefore the number of moles of Cu2+= 0.00125/65.55 = 1.97x10^-5 moles

$Cu^{2+}_{(aq)}+Na_{2}CO_3_{(s)}\rightarrow CuCO_{3}_{(s)}+2Na^{+}_{aq}$

It can be seen that number of moles of Cu2+ = number of moles of CuCO3
therefore 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)

2010 Chemistry qn20 mc (1 Viewer)

forthehsc

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b3kh1t

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