28 Solubility Product Problems

28 Solubility Product Problems - Which Salt to Buy for...

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1 1 Which Salt to Buy for De-icing? Four salts commonly are sold for ice melting. Which one would you purchase in order to get the most ions per dollar spent assuming they all cost $1/lb? 1 lb = 455 g A) NaCl (aka halite, 58 g/mol) B) KCl (75 g/mol)) C) CaCl 2 (111 g/mol) D) MgCl 2 (95 g/mol) Do you remember? T f = - K f m solute i solute mol ions mol i g/mol 1 lb g 455 $ lb 1 $ ions mol 2 Which Salt to Buy for De-icing? A) NaCl (58 g/mol, H sol = +3.9 kJ/mol) Use this as the standard, assume price $1.00/lb 1 lb 15.7 mol ions/$1 B) KCl (75 g/mol), H sol = +17 kJ/mol 1 lb 12.1 mol ions/$1 so cost should be $.77/lb C) CaCl 2 (111 g/mol, H sol = -81 kJ/mol) 1 lb 12.3 mol ions/$1 so cost should be $0.78/lb D) MgCl 2 (95 g/mol, H sol = -133 kJ/mol) 1 lb 14.4 mol ions/$1, so cost should be $0.91/lb Note: It is reported that MgCl 2 is the least harmful to surfaces and plants. Probably because it is almost as effective as NaCl per pound and magnesium nitrate and sulfate are added to fertilizers so the Mg 2+ is better than Na + . It also is the most exothermic.
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2 3 Solubility Equilibria and the Solubility Product Constant, K sp (MSJ Ch. 17.4 – 17.6) Consider silver sulfate dissolving in water Ag 2 SO 4 (s) 2 Ag + (aq) + SO 4 2- (aq) Write the equilibrium constant expression.
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This note was uploaded on 04/17/2010 for the course CHE 132 taught by Professor Hanson during the Spring '08 term at SUNY Stony Brook.

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28 Solubility Product Problems - Which Salt to Buy for...

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