Question

A \(475-\mathrm{mL}\) sample of water is extracted from a well and analyzed for mercury. The mercury content is found to be \(0.005 \mathrm{mg}\). What is the concentration of mercury in the well water in milligrams per liter? Is the water safe for human consumption?

Short answer

The concentration is 0.0105 mg/L. The water exceeds EPA standards for mercury and is not safe for consumption.

Step-by-step solution

Convert volume to liters

Since concentration is commonly expressed in milligrams per liter (mg/L), convert 475 mL to liters by dividing by 1000, because there are 1000 milliliters in a liter.

Compute concentration

Use the formula for concentration in mg/L which is the mass of the substance (in milligrams) divided by the volume of the solution (in liters).

Compare with safety standards

Compare the computed concentration with the Environmental Protection Agency (EPA) standard for mercury in drinking water, which is 0.002 mg/L.

Key concepts

Chemical Concentration Calculation

Understanding the concentration of chemicals in a solution is crucial for assessing the potential impact on health and the environment. In simple terms, concentration refers to how much of a substance is present in a certain amount of a solution. In environmental chemistry, this is especially important when evaluating pollutants, such as mercury in water.

For the provided exercise, calculating the concentration involves two steps. First, one needs to know the mass of the substance present, which is given as 0.005 mg of mercury. Second, you must determine the total volume of the solution, which is the water sample from the well. Here, the volume needs to be in liters to match the common concentration units of mg/L (milligrams per liter).

The formula used for the calculation is:
\[ \text{Concentration} = \frac{\text{Mass of substance (mg)}}{\text{Volume of solution (L)}} \]
The mercury concentration is determined by dividing the mass of mercury by the volume of water in liters. This calculation helps determine if the water meets health safety standards.

Volume Conversion

Understanding volume conversion is essential in chemical concentration calculations because different regions and scientific disciplines use various measurement units. In the exercise, the water sample volume is given in milliliters (mL), but concentration is typically expressed in mg/L.

To convert milliliters to liters, you need to know the basic conversion factor:
\[1 \text{ liter } = 1000 \text{ milliliters}\]
Thus, you convert the volume of the water sample from mL to L by dividing by 1000, which simplifies the calculation and standardizes the measurement for comparison purposes.

For the exercise, converting 475 mL to liters is done by this calculation:
\[475 \text{ mL} \times \frac{1 \text{ L}}{1000 \text{ mL}} = 0.475 \text{ L}\]
This step is imperative to align with the standard units used in the concentration formula.

Environmental Chemistry

Environmental chemistry is the scientific study of the chemical and biochemical phenomena that occur in natural places. It involves understanding how contaminants like mercury enter the water supply and assessing their concentrations to determine potential risks.

In relation to the exercise, once the concentration of mercury in the water is calculated, it must be compared to safety standards, which are established based on research into the health effects of exposure to various chemical levels.

The Environmental Protection Agency (EPA) has set the maximum contaminant level for mercury in drinking water at 0.002 mg/L. If the concentration of mercury in the water sample exceeds this limit, it would be considered unsafe for human consumption. This comparison is an example of applying environmental chemistry principles to ensure public health and safety.