30 Electrochemistry1

30 Electrochemistry1 - How many moles of NaCl must be added...

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1 How many moles of NaCl must be added to 10 L of a 1.0 M solution of Pb(NO 3 ) 2 to bring it to the threshold of precipitating PbCl 2 (K sp = 1.7x10 -5 )? Assume the volume doesn’t change. A) 4.1x10 –3 B) 4.1x10 –2 C) 1.7x10 –4 D) 1.7x10 –3 E) 1.0 2 How many moles of NaCl must be added to 10 L of a 1.0 M solution of Pb(NO 3 ) 2 to bring it to the threshold of precipitating PbCl 2 (K sp = 1.7x10 -5 )? Assume the volume doesn’t change. A) 4.1x10 -3 B) 4.1x10 -2 C) 1.7x10 -4 D) 1.7x10 -3 E) 1.0 NaCl mol 10 4.1 need so L 10 have but M 10 4.1 x M)(x) (1 10 1.7 K x 1M : ld At thresho (aq) 2Cl (aq) Pb (s) PbCl 2 - 3 - 2 5 - sp - 2 2 x x x
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3 What do you predict? A) Silver metal will dissolve in a salt solution of copper nitrate. B) Copper metal will dissolve in a salt solution of silver nitrate. C) Both (A) and (B) will happen because salt solutions are corrosive. D) Neither (A) nor (B) will happen because metals are stable. 4 B) Copper dissolves in a salt solution of silver nitrate. Cu(s) + 2Ag + (aq) Cu 2+ (aq) + 2Ag(s)
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5 Why does this happen? The free energy decreases! G = H - T S Entropy probably deceases because 2 ions in solution go to 1! So reaction would have to be exothermic. 2 silver atoms are more strongly bound in the metal lattice than 1 copper atom. Compare enthalpies of fusion 1 mol Cu 13.1 kJ 2 mol Ag 22.6 kJ/mol Cu(s) + 2Ag + (aq) Cu 2+ (aq) + 2Ag(s) 6 What type of a reaction is this? Notice electrons are transferred from copper atoms to silver atoms. Electron transfer reaction Oxidation – reduction reaction (aka redox) Electrochemical reaction Note the charge must be balanced to conserve electrons. Review MSJ Ch 5, sections 3 & 4 oxidation numbers MSJ Ch 19 Electrochemistry, pp. 920 – 976 Cu(s) + 2Ag + (aq) Cu 2+ (aq) + 2Ag(s)
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7 Today’s To Do Write definitions of oxidation, reduction, oxidizing agent, and reducing agent.
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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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30 Electrochemistry1 - How many moles of NaCl must be added...

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