Answer to Question #254538 in Chemistry for Katerina

Question

a) Calculate the molarity of a 5 ppm pesticide solution if the molar mass of the pesticide

435 g/mol.

b) Seawater contains 3.90 x 10¯ 3 ppb of dissolved gold. What volume (in litres) of this seawater would contain 100 g of gold?

Answer 1

a) CM = n /V

n = m /M

5 ppm = 5 mg/L

5 mg = 0.005 g

n = 0.005 / 435 = 0.00001 mol

For 1 litre of solution the molarity is:

C_M = 0.00001 / 1 = 0.00001 M

b) 1 ppb = 1 microgram / L = 0.000001 g/L

V = 100 / 0.000001 = 100 000 000 L will contain 100 g of gold.