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Ees413:Aquatic Chemistry Question Paper

Ees413:Aquatic Chemistry

Course:Aquatic Chemistry

Institution: University Of Eldoret question papers

Exam Year:2014

Answer all questions in section A and any four in section B
section A
1.Construct the equation for the reaction between manganate (VII) ions and iron(II) ions in aqueous acidic solution (4marks)
2.Integrate the differential equation for the first order reaction rate (3marks)
3.Specify the units in for all quantities involved in the equation Q 2?(marks)
4.Urea,NH2CONH2 is an important agricultural chemical.The following are STD enthalpies of formation at 25degreesCelsius for the reactants and products(kJ/mol):
NH3(g),-45.9;CO2(g) ,-393.5;NH2CONH2(aq),-319.2;H2O (l),-285.8
Calculate the change of heat of the reaction(3marks)
5.Explain the meaning of the term ''amphiprotic species''?(3marks)
6.Given that the pOH of an aqueous solution is 8.Calculate its pH(2marks)
7.What is the Lewis acid?Illustrate your answer using the reaction between Al3+ and H2O(3marks)
8.What is the pH of a solution whose hydroxide ion concentration is 4.0x10^-4 mol/L ?Is the solution acidic or basic?(3marks)
9.Silicate is basically a compound of silicon and oxygen with one or more metals that may be formally regarded as a derivative of silicic acid in aqueous solution.Write down the condensation reaction of silicic acid anions (3marks)
10.Illustrate graphically the buffering effect of CO2 in natural waters(4marks)
section B
11.Briefly describe the following variables that affect chemical reaction rate in aquatic environment:
a.Physical state(4marks)
b.Concentration (3marks)
c.Temperature (3marks)
12.Using CaC2O4 and CaCl2 as an example:
a.Show the importance of solubility constant (Ksp) and the common ion effect at equilibrium(5marks)
b.What is the molar solubility of calcium oxalate in 0.15M calcium chloride?(Ksp for CaC2O4(s) is 2.3 x10^-9)(5marks)
13.Organic matter arising from living organisms makes an important contribution to the natural quality of surface waters.Describe:
a.Formation,and composition of humic acids in natural waters (6marks)
b.Chemical characteristics of humic substances (4marks)
14.Henderson-Hassel balch equation may be used ,among other things ,in the preparation of buffer solution of known pH:
a.Derive Henderson-Hassel balch equation(6marks)
b.Given that Ka of the conjugate acid NH4+ is 5.6x10^-10,calculate the pH of a buffer solution containing 0.10MNH3 and 0.20MNH4Cl at 25 degrees celsius(4marks)
15.Eldoret waste water stabilization pond initial organic load measurements show a BOD concentration of 200mg/L.Three days later the BOD concentration is 100mg/L.
A.Calculate the BOD concentration in the pond after a week (assume biodegration rate is first order reaction)(4marks)
b.How long will it take for the BOD concentration levels to reach the Kenyan effluent discharge standard requirement concentration level?(3marks)
2.Plot the BOD concentration against time(graph paper provided)(3marks)
16.Briefly describe the hydrological cycle(10mark7
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Ees413:Aquatic Chemistry Question Paper

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