Question

1) The maximum allowable concentration of lead in drinking water is 9.0 ppb. (a) Calculate the molarity of lead in a 9.0-ppb solution. What assumption did you have tomake in your calculation? (b) How many grams of lead are in a swimming pool containing 9.0 ppb lead in 60 m3 of water?

Answer 1

a.

Maximum allowable concentration of Pb is i.e.

Moles of Pb can be calculated from its molar mass as

As the amount of Pb is very less in comparison to water, it can be assumed that the density of solution is equal to density of water i.e.

Hence, volume of solution becomes

Molarity of Pb in water sample can be calculated as

Hence, molarity of Pb in water sample is

b.

In swimming pool, moles of Pb can be calculated from molarity as

Mass of Pb in grams can be calculated from its molar mass as

Hence, mass of Pb present in swimming pool is