Question

You have prepared a solution by dissolving 254.61mg of copper(II) nitrate pentahydrate in 1.25kg of water. What is this solution's Cu⁺² concentration in parts per million, ppm?

Answer 1

ppm is parts per million.

1 ppm = 1 mg of solute in1 L of solution .

or

1 ppm = 1 mg of solute in 1 kg of solution [ 1 L = 1000 ml = 1000 g , d = 1g/ml]

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Given 254.61 mg of copper(II) nitrate pentahydrate in 1.25 kg of water.

$Cu(NO_{3})_{2}.5H_{2}O\rightarrow Cu^{2+}+2NO_{3}^{-}+5H_{2}O$

$1Equivalent of Cu(NO_{3})_{2}.5H_{2}O\equiv 1Equivalent ofCu^{2+}$

$\therefore$ Molar mass of Cu(NO3)2.5H2O = 232.6 g/mol

Number of moles in 254.61 mg of Cu(NO3)2.5H2O = mass /MW

= (254.61 mg /232.6 g/mol*1000)

= 0.0010946 moles

Therefore ,

0.0010946 moles of Cu(NO3)2.5H2O = 0.0010946 moles of Cu^2+ ion

SO mass of 0.0010946 moles of copper ion = moles * Atomic mass of Cu

= 0.0010946 moles * 63.55 g/mol

=0.06956 g of copper ion

So 0.06956 g of copper ion present in 1.25 kg of water.

OR

69.56 mg of copper ion present in 1.25 kg of water

mass of copper ion present in 1 kg of water = 69.56 mg / 1.25 kg

= 55.65 mg / Kg

So it is expressed in ppm as 55.65 ppm