The total amount of nitrogen from fertilizer that is washed into a river is 1.80 × 105 mg per year. The river flows through the field at a rate of 600,000 liters per year (6.00 x 105 L/yr).

Question

What is the concentration of nitrogen (expressed in milligrams of nitrogen per liter) in the river from the farmer's fertilizer?

Answer 1

Given: In 1 yr the mass of nitrogen in liquid (river) is m = 1.80 x 10⁵ mg,

and the volume of liquid is V = 6.00 x 10⁵ L

Concentration = ^{mass (mg)}/_{volume (L)} = ^{1.80 x 105 mg} / _{6.00 x 10^5} = 0.300 mg/L