Question

The current maximum level of fluoride that the EPA allows in U.S. drinking water is \(4 \mathrm{mg} / \mathrm{L}\). Convert this concentration to molarity.

Short answer

The molarity is approximately \(2.1 \times 10^{-4} \text{ mol/L}.\)

Step-by-step solution

Understand the Question

We need to convert the given fluoride concentration from mass per volume \(\text{mg/L}\) to molarity \(\text{mol/L}\).

Identify Given Values

The concentration of fluoride is given as \(4 \text{ mg/L}\). The molar mass of fluorine \(\text{F}\) is about \(19.00 \text{ g/mol}\).

Convert mg to g

Convert the mass of fluoride from milligrams to grams to use the molar mass for conversion. Since \(1 \text{ mg} = 0.001 \text{ g}\), we have:\[4 \text{ mg/L} = 0.004 \text{ g/L}\]

Use Molar Mass to Find Moles

To find the molarity, we divide the mass of fluoride in grams by its molar mass in grams per mole:\[\text{Moles of } F = \frac{0.004 \text{ g/L}}{19.00 \text{ g/mol}}\]

Calculate Molarity

Perform the division to get molarity:\[\text{Molarity} = \frac{0.004}{19.00} \approx 2.1 \times 10^{-4} \text{ mol/L}\]

Key concepts

Molarity Conversion

Molarity is a fundamental concept in chemistry that quantifies the concentration of a solute in a solution. Specifically, it represents the number of moles of a solute per litre of solution, denoted as \text{mol/L}. To convert from terms like \text{mg/L} to molarity, we first need to understand the relationship between mass, moles, and volume.

**Key Steps in Conversion**

• Convert Units: Begin by converting the mass from milligrams to grams because molarity calculations typically require mass in grams. This involves using the conversion \(1 \ ext{ mg} = 0.001 \ ext{ g}\).
• Determine Moles: Use the molar mass of the element or compound (grams per mole) to convert grams to moles. Moles are the bridge between the amount of substance and its chemical individuality.
• Calculate Molarity: Finally, divide the number of moles of solute by the volume of the solution in litres to find molarity.

This systematic approach ensures precise conversion, facilitating accurate representation of solution concentrations.

Fluoride Concentration

Fluoride concentration in water is an important parameter, especially in drinking water. It is typically expressed in terms of mass per volume, such as \text{mg/L}. To transform this into molarity, understanding fluoride's molar mass is crucial.

**Importance of Measuring Fluoride**

• Fluoride helps in preventing tooth decay when present at safe levels.
• Too much fluoride can lead to health issues like dental fluorosis.

**Fluoride Conversion to Molarity**

• Given Value: Begin with the fluoride concentration given in \(4 \ ext{ mg/L}\).
• Molar Mass of Fluoride: Using the molar mass of fluorine (19.00 g/mol) helps convert this value to molarity.

Understanding these transformations enables better monitoring and regulation of fluoride in water supplies, ensuring safety and compliance with standards.

Molar Mass Calculation

Molar mass is pivotal in converting concentration units to molarity in chemistry. For this purpose, you need a firm grasp of its significance and calculation method.

**Definition and Usage**

• Molar Mass: The mass of one mole of a substance, usually in grams per mole. It's calculated by summing the atomic masses of the constituent atoms in a molecule.
• Conversion Role: Knowing the molar mass allows the transformation from grams (or milligrams) to moles, which is an essential step in determining molarity.

**Example with Fluorine**

The element fluorine has a molar mass of 19.00 g/mol, used to convert its mass to moles.

This allows the conversion of concentration from \(4 \ ext{ mg/L}\) to molar, showing the chemical presence in terms of molecular substance amount.

Calculating molar mass is a versatile skill in chemistry, crucial for diverse applications in laboratory and environmental sciences.

EPA Drinking Water Standards

The Environmental Protection Agency (EPA) sets regulations to protect human health by controlling contaminants in drinking water. Fluoride levels are particularly important given their health implications.

**Objective of EPA Standards**

• Ensure safe consumption levels of potentially beneficial yet harmful substances, like fluoride.
• Maintain a balance that minimizes health risks associated with overexposure.

**Fluoride Regulation**

• The EPA's maximum contaminant level for fluoride is \(4 \ ext{ mg/L}\), ensuring that drinking water contributes positively to dental health without adverse effects.
• Regular monitoring and conversion to molarity help in precise, scientifically rigorous assessments of water safety.

Adhering to EPA standards not only ensures public safety but also instills public confidence in water safety and quality assurance measures.