The level of mercury in a stream was suspected to be above...

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 $1.0 \mathrm{g} / \mathrm{mL}$ and calculate the molarity of mercury in the stream.

Key Concepts

Density in Unit Conversion

Density is a physical property that relates the mass of a substance to its volume. In many chemical calculations, assuming the density (e.g., 1.0 g/mL for water) allows one to convert between mass and volume measurements. This is particularly useful when converting a concentration given in mass per unit mass (such as ppb by weight) into a mass per unit volume, which can then be used to calculate molarity.

Parts Per Billion (PPB) Concentration

Parts per billion is a unit of concentration that denotes one part of a substance for every billion parts of the total. In environmental chemistry, it is often used to express very low concentrations of contaminants, and it typically refers to a mass ratio (by weight) where, for example, 1 ppb means 1 part of solute per billion parts of solution.

Molarity

Molarity is a measure of the concentration of a solute in a solution, defined as the number of moles of solute per liter of solution. It is a fundamental concept in chemistry used to relate the amount of a chemical species to the volume of the solution, making it crucial for quantitative analyses and reaction stoichiometry.

Molar Mass and Mole Concept

The mole concept enables the conversion between the mass of a substance and the number of its moles using the substance's molar mass. Molar mass, typically expressed in grams per mole, is the mass of one mole of a substance and is essential in calculations that convert a mass-based concentration (like ppb) into molarity.

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