Mercury is a stream is 0.68ppb by mass. How many grams of mercury are present in 15.0L of the stream of water( assuming the density of water is 0.998g/mL)?

Question

Would you divide 0.68ppb as mass over 0.998g/mL and then times that by 15.0L? 

Answer 1

0.78 ppb = 0.78 mg/10³ liters

0.78 mg/10³ liters x 15.0 liters = 1.17x10⁴ mg of mercury present in 15.0 liters = 11.7 g of mercury present in 15 liters

If you want the grams of mercury per gram of water, then you use the density of water (0.998 g/ml or 998 kg/L)

11.7 g mercury/15.0 L x 1 L/1000 ml x 1 ml/0.998 g = 0.000782 g mercury/g water

11.7 g mercury/(14970 g water) = 0.000782 g mercury/g water