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) t = S/Q

t = 12,500 Km3 / 140 km3/year = 89.29 years

t = 89.29 years x 365 days/1 year = 32590.85 or 32591 days.

b) Innitial concentration C = 15 ug/L

Molar mass of P = 31 g/mol

15 ug x 0.000001 g/ug = 0.000015 or 1.5x10-5 g/L

M = 1.5x10-5 g/L / 31 g/mol = 4.8387x10-7 mol/L

m = 4.8387x10-7 / 1.5x10-5 = 0.032258 mol/g x 1000 g/kg = 32.258 mol/kg

ppm = 32.258 mol/kg x 31 g/mol = 999.998 g/kg x 1000 mg/g = 999,998 mg/kg

c) The Water is the universal solvent basically because it has the following properties:

Water, which not only dissolves many compounds but also dissolves more substances than any other liquid, is considered the universal solvent. A polar molecule with partially-positive and negative charges, it readily dissolves ions and polar molecules. Water is therefore referred to as a solvent: a substance capable of dissolving other polar molecules and ionic compounds. The charges associated with these molecules form hydrogen bonds with water, surrounding the particle with water molecules. This is referred to as a sphere of hydration, or a hydration shell, and serves to keep the particles separated or dispersed in the water.

When ionic compounds are added to water, individual ions interact with the polar regions of the water molecules during the dissociation process, disrupting their ionic bonds. Dissociation occurs when atoms or groups of atoms break off from molecules and form ions. Consider table salt (NaCl, or sodium chloride): when NaCl crystals are added to water, the molecules of NaCl dissociate into Na+ and Cl– ions, and spheres of hydration form around the ions. The positively-charged sodium ion is surrounded by the partially-negative charge of the water molecule's oxygen; the negatively-charged chloride ion is surrounded by the partially-positive charge of the hydrogen in the water molecule.

Also, The strong hydrogen bonds give water a high cohesiveness and, consequently, surface tension. This is evident when small quantities of water are put onto a nonsoluble surface and the water stays together as drops.

Pure water is actually a good insulator (poor conductor), meaning that it does not conduct electricity well. Because water is such a good solvent, however, it often has some solute dissolved in it, most frequently salt. If water has such impurities, then it can conduct electricity much better, because impurities such as salt comprise free ions in aqueous solution by which an electric current can flow.

Water can be split into its constituent elements, hydrogen and oxygen, by passing a current through it. This process is called electrolysis. Water molecules naturally disassociate into H+ and OH- ions, which are pulled toward the cathode and anode, respectively.

I hope This can help you.

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