ENV4001 Assignment 1 Answer

# ENV4001 Assignment 1 Answer - 4 2 Assume X mol[Ca 2 and X...

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1 G. Chen Summer 2011 ENV4001 Environmental Engineering Problem Set #1 1. Cesium-137 is a radionuclide. It takes around 1.5 10 5 days for Cesium-137 to decay to one-third of its concentration. When 5 curies of Cesium-137 is blown into the upper atmosphere, approximately how much Cesium-137 eventually returns to earth if its typical residence time in the atmosphere is 4 years? (Note: the Curie is a unit of radioactivity. Radionuclide decay is a first order reaction.) 2. Calcium hydroxyl [Ca(OH) 2 ] is added to pure water. If solid Ca(OH) 2 remains at equilibrium, what is the equilibrium molarity of calcium ions at 25 o C? What is the equilibrium molarity of OH - ?

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2 3. Calcium sulfate (CaSO 4 ) is added to 10 -3 M CaCl 2 solution. If solid CaSO 4 remains at equilibrium, what is the equilibrium molarity of calcium ions at 25 o C?  Solution: ] SO ][ Ca [ K 2 4 2 sp Since there is an initial [Ca 2+ ] in the solution, [Ca 2+ ] [SO
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Unformatted text preview: 4 2-] Assume X mol [Ca 2+ ] and X mol [SO 4 2-] were dissociated from CaSO 4 . Now in the solution, [Ca 2+ ] = X + 10-3 M; while [SO 4 2-] = X . M 10 . 4 2 10 2 1 4 ) 10 ( 10 X X 10 X X ) 10 X ( ] SO ][ Ca [ K 3 5 2 3 3 3 2 3 2 4 2 sp Final answer: [Ca 2+ ] = 4.0 × 10-3 + 10-3 = 5.0 × 10-3 M 4. Using standard free energies, what is the equilibrium constant for the dissociation of acetic acid ( COO CH H COOH CH 3 3 ) at standard conditions? Solution: COO CH H COOH CH 3 3 3 G = G 298 (CH 3 COO-) + G 298 (H + ) - G 298 (CH 3 COOH) = -89.0 + 0 – (-95.51) = 6.51 (Kcal/mole) 5 99 . 10 10 69 . 1 e K 99 . 10 K 298 ) Kmole /( Cal 987 . 1 mole / kCal 51 . 6 RT G LnK...
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ENV4001 Assignment 1 Answer - 4 2 Assume X mol[Ca 2 and X...

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