The environmental protection agency allows 10 ppb concentration of arsenic in drinking water. What is the molarity of As in this solution?
To find the molarity of arsenic (As) in the solution, we need to convert the given part per billion (ppb) concentration to molarity.
Step 1: Understand the Conversion Factor:
1 ppb = 1 part per billion = 1 microgram per liter (μg/L)
Note: This conversion factor is based on the assumption that the molecular weight of the compound is close to 1 gram/mol.
Step 2: Calculate the Molarity:
The molarity (M) is defined as the number of moles of solute per liter of solution.
Given:
Concentration = 10 ppb
To convert ppb to molarity, we need to convert ppb to μg/L and then to grams/L by dividing by the atomic mass of arsenic. Finally, we will convert grams to moles by dividing by the molar mass of arsenic.
Atomic Mass of Arsenic (As) = 74.92 g/mol (approximate)
Converting ppb to μg/L:
10 ppb = 10 μg/L
Converting μg/L to g/L:
10 μg/L = 10/1000000 g/L (since 1 μg = 1/1000000 g)
Converting g/L to mol/L:
10/1000000 g/L = (10/1000000 g) / (74.92 g/mol)
Calculating the Molarity:
Molarity (M) = (10/1000000 g) / (74.92 g/mol)
Simplifying the calculation:
Molarity (M) = 0.000133 mM (approximately)
So, the molarity of arsenic (As) in the solution with a concentration of 10 ppb is approximately 0.000133 mM.