Question

A sample of 450.0 g of water is found to contain 180 mg Cd. What is this concentration in parts per million?

Answer 1

Answer:

The correct answer is 399.8 ppm

Explanation:

A concentration in parts per million (ppm) is equal to:

$1 ppm = \frac{1 g solute}{10^{6}g solution}= \frac{1 mg solute}{1 kg solution}$

Solute: Cd; Mass = 180 mg x (1 g/1000 mg) = 0.18 g

Solvent: Water ; Mass= 450.0 g x (1 kg/1000 g) = 0.45 kg

We have the following total mass of solution:

Mass of solution = Mass of solute + Mass of solvent = 0.18 g + 450 g = 450.18 g = 0.45018 kg

Finally, we divide the mass of solute (in mg) into the mass of solution (in kg) to obtain the ppm (in mg/Kg):

ppm = 180 mg/0.45018 kg = 399.8 mg/Kg = 399.8 ppm