Question

the epas standard for lead in bare soil in play areas is 400 ppm by weight. you determine that a 350 gram sample of soil from a local park has 220 mg of lead present. how much lead is present in ppm?
6300 ppm
630 ppm
63 ppm
6.30 ppm

Explanation:

Step1: Convert grams to milligrams

Since 1 g = 1000 mg, a 350 - gram sample is $350\times1000 = 350000$ mg.

Step2: Calculate ppm

The formula for ppm (parts - per - million) is $\text{ppm}=\frac{\text{mass of solute (mg)}}{\text{mass of solution (mg)}}\times10^{6}$. Here, the mass of the solute (lead) is 220 mg and the mass of the solution (soil) is 350000 mg. So, $\text{ppm}=\frac{220}{350000}\times10^{6}$.
$\frac{220\times10^{6}}{350000}=\frac{220\times10^{6}}{3.5\times10^{5}}=\frac{220}{3.5}\times10=\frac{2200}{3.5}\approx628.57\approx630$ ppm.

Answer:

630 ppm