Question

According to the EPA, the maximum contaminant level (MCL) of antimony in drinking water is 0.0060 mg/L. (a) Convert the MCL of antimony from milligrams per liter to parts per billion (ppb). (b) A farmer has recently dug a new well for his property. He sends a 10.0 mL sample of the well water to the EPA to be tested for the presence of antimony. What is the maximum amount of Sb (in μg) that can be present in this 10.0 mL sample based on its MCL? (c) Suppose the farmer has rethought his plan and dug a new well on the other side of his property. He sends a new 10.0 mL sample. After testing, the EPA determines that the sample of water contains 0.00100 μg/mL Sb. Is the well water safe to consume?

Answer 1

a) 1 ppb = Solute present at one-billionth of a gram per gram of sample solution = 10^-9 g of solute / 1 g of solution

     For water, mass of 1 mL is 1 g. Thus for a water solution,

1 ppb = 10^-9 g of solute / mL = 10^-6 g of solute / L

Hence, MCL of antimony in ppb = .0060mg/L = ( 0.006/1000) g/L = (6 * 10^-6) g/L = 6 μg /L

b) Maximum level of Sb in 10 mL sample

= (6 × 10) / 1000 μg

= 0.06 μg

c) 0.001 μg/mL

= ( 0.001 * 1000) μg / L

= 1 μg/L < 6 μg/L

The well water is safe to consume.