The Safe Drinking Water Act (SDWA) sets a limit for mercury—a toxin to the central nervous system—at 0.0020 ppm by mass. Water suppliers must periodically test their water to ensure that mercury levels do not exceed this limit. Suppose water becomes contaminated with mercury at twice the legal limit (0.0040 ppm). How much of this water would a person have to consume to ingest 50.0 mg of mercury?

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Determine the concentration of mercury in the water in terms of mg/L. Since 1 ppm is equivalent to 1 mg/L, the concentration of mercury in the contaminated water is 0.0040 mg/L.

Set up the equation to find the volume of water needed to ingest 50.0 mg of mercury. Use the formula: \( \text{Mass of mercury} = \text{Concentration of mercury} \times \text{Volume of water} \).

Rearrange the equation to solve for the volume of water: \( \text{Volume of water} = \frac{\text{Mass of mercury}}{\text{Concentration of mercury}} \).

Substitute the known values into the equation: \( \text{Volume of water} = \frac{50.0 \, \text{mg}}{0.0040 \, \text{mg/L}} \).

Calculate the volume of water needed to ingest 50.0 mg of mercury, ensuring to keep track of units and converting them if necessary to more understandable units like liters or gallons.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Parts Per Million (ppm)

Parts per million (ppm) is a unit of measurement used to describe the concentration of a substance in a solution. It indicates how many parts of a substance are present in one million parts of the total solution. For example, a concentration of 0.0020 ppm means that there are 0.0020 grams of mercury in one million grams of water, which is crucial for understanding contamination levels in drinking water.

Mass and Volume Relationships

Understanding the relationship between mass and volume is essential for solving problems involving concentrations. In this context, knowing the density of water allows us to convert between mass (in mg) and volume (in liters or milliliters). This relationship helps determine how much contaminated water a person would need to consume to reach a specific mass of mercury.

Toxicology and Safe Exposure Levels

Toxicology is the study of the effects of chemicals on living organisms, including the assessment of safe exposure levels. The Safe Drinking Water Act establishes limits for contaminants like mercury to protect public health. Understanding these limits is vital for evaluating the risks associated with consuming contaminated water and determining how much water would lead to harmful exposure.

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