Question

The level of mercury in a stream was suspected to be above the minimum considered safe (1 part per billion by weight). An analysis indicated that the concentration was 0.68 parts per billion. Assume a density of 1.0 g/mL and calculate the molarity of mercury in the stream.

a) 6.8 x 10⁻⁷ M
b) 6.8 x 10⁻⁴ M
c) 6.8 x 10⁻¹ M
d) 6.8 x 10⁻¹⁰ M

Answer 1

To calculate the molarity of mercury in the stream, convert the concentration from ppb to molarity by multiplying by the density of water, dividing by the molar mass of mercury, and converting to millimoles per liter.

Step-by-step explanation:

To calculate the molarity of mercury in the stream, we need to convert the concentration from parts per billion (ppb) to molarity. Here are the steps:

1. Convert the given concentration of 0.68 ppb to grams per liter (g/L) by multiplying it by the density of water (0.998 g/mL).
2. Convert grams per liter to moles per liter (M) by dividing the grams by the molar mass of mercury (200.59 g/mol).
3. Finally, divide the moles per liter by 1000 to convert to millimoles per liter (mM).

By following these steps, we find that the molarity of mercury in the stream is approximately 6.8 x 10-7 M.