Question

The concentration benzene (C6H6) in a sample of groundwater was 25.9 ppb. This was the molar concentration of benzene in that water sample:

O 3.32 x 10⁻⁷ M
O 5.71x 10⁻⁷ M
O 9.86 x 10⁻⁷ M
O None of the above

Answer 1

The concentration of benzene in a groundwater sample at 25.9 ppb converts to a molar concentration of 3.32 x 10^-7 M, which is determined by dividing the mass of benzene in micrograms by the molar mass of benzene in grams per mole.

option a is the correct

Step-by-step explanation:

The concentration of benzene (C6H6) in groundwater at 25.9 ppb needs to be converted to its molar concentration. To accomplish this, we first convert parts per billion (ppb) to a mass concentration, considering units where 1 ppb is equivalent to 1 microgram per liter (ug/L). Given the molecular weight of benzene is approximately 78.11 g/mol, the molar concentration can be calculated using the formula: molarity = (mass of solute in grams) / (molar mass of solute in grams per mol * volume of solution in liters).

To find the number of moles in 25.9 ug of benzene: moles = (25.9 ug) / (78.11 g/mol * 106 ug/g)

This calculates to approximately 3.32 x 10-7 moles of benzene per liter, which is the molar concentration of benzene in that water sample. Therefore, the correct option is: 3.32 x 10-7 M.