[Dan12]

Hi I'm just stuck on some chemistry review concentration questions.

a) A 1.05 L sample of groundwater with a density of 1.002 kg/m3 from an oil spill site contains 0.092 mM of benzene (C6H6). What is the mass of C contained in benzene in this sample?

1 mM = 10-3 mol/L => 0.092 mM = 9.2*10-5 mol/L
Benzene molar mass = 78.11 g/mol

(1.05 L) * (9.2*10-5 mol/L) * ((12.01 * 6) g/mol) = 6.96*10-3 g * (1 kg/1000 g) = 7.0*10-6 kg

[Is this right?]

b) A 6.2 ounce substance contains 0.199 μg/g of mercury. How many micromoles of Hg does it contain?

For this one, I'm not even sure what to do with the "0.199 μg/g of mercury." Is it something to do with PPM? 

c) A lake contains 12,100 km3 of fresh water, with an average concentration of 2.5 μg/L of P.  Assuming all P is present as PO42-, how many grams of PO42- does it contain?

Thank you for any help.

[Borek]

[Is this right?]

Looks OK.

I'm not even sure what to do with the "0.199 μg/g of mercury."

Each gram of the sample contains 0.199 μg of mercury.