Question

calculating ppm: practice

1. if a mass of 12.0 mg of mercury is dissolved in 100 kg of water, what is the concentration of mercury in ppm?

Explanation:

Step1: Convert units

Convert \(100\ kg\) of water to \(mg\). Since \(1\ kg = 10^{6}\ mg\), then \(100\ kg=100\times10^{6}\ mg = 10^{8}\ mg\).

Step2: Use ppm formula

The formula for parts - per - million (ppm) is \(ppm=\frac{\text{mass of solute (mg)}}{\text{mass of solution (mg)}}\). The mass of solute (mercury) \(m = 12.0\ mg\), and the mass of solution (assuming the mass of solution is approximately equal to the mass of solvent since the mass of solute is very small) \(M=10^{8}\ mg\). Then \(ppm=\frac{12.0\ mg}{10^{8}\ mg}\).

Step3: Calculate ppm

\(\frac{12.0}{10^{8}}=1.2\times 10^{-7}\)

Answer:

\(1.2\times 10^{-7}\) ppm