HEY NEED URGENT HELP WITH THESE CHEM QUESTIONS! thank you!!! 11. Residence time

Question

HEY NEED URGENT HELP WITH THESE CHEM QUESTIONS! thank you!!!

11. Residence time and solutes in water (see Radojevic, Chapt. 1)

(a) The volume of water in Lake Michigan is about 12,500 km3 . The flux of water into the lake is estimated at about 140 km3 per year. What is the residence time of water in the lake?

(b) The Great Lakes suffered severe pollution during over the last 50 years from the influx of excess nutrients, primarily phosphorus (P) and nitrogen (N) from fertilizers, which caused large phytoplankton blooms and subsequent anoxia.

Water quality has improved in the upper Great 3 Lakes (Superior, Michigan, and Huron), but the lower lakes (Erie and Ontario) are still impacted. Lake Erie, which is adjacent to a high density of industrial and agricultural run-off sources, continues to receive a high influx of phosphorus.

According to the EPA, concentrations of total P in Lake Erie fluctuate around a mean of about 15 ug L-1 (micrograms per liter). What is the mean concentration of P in Lake Erie in M (mol L-1 )? in m (mol kg-1 )? in ppm?

(c) Briefly explain what properties of water make it a good solvent for both inorganic oxyanion species such as phosphate (H3-xPO4 -x ) and organically bound phosphorus?

Explanation / Answer

(a)

Residence time = Volume of water in lake / Flux of water in the lake

Residence time = 12,500 km^3 / 140 km^3/year = 89.286 years

(b) Concentration of P = 15 ug/L = 15 x 10^-6 g/L

Now,

Concentration of P in mol/L = 15 x 10^-6 / 31 = 4.84 x 10^-7 mol/L

moles of solute = 4.84 x 10^-7 mol

Volume of solution = volume of solvent = 1000ml

mass of solvent = 1000 g = 1kg

molality = 4.84 x 10^-7 mol/kg

1 ug/ml = 1 ppm

1 ug/L = 0.001 ppm

15 ug/L = 0.015 ppm

(c) Water is polar in nature so it readily dissociates into ions thus forming bonds and reacting with inorganic oxyanion phosphorus.

Water is formed in photosynthesis reaction which involves ADP which is organically bound phosphorus . So , water ca n actually be formed from organically bound phosphorus .

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