30 SelectivePrecip&amp;LargeK

# 30 SelectivePrecip&amp;LargeK - How many moles of NaCl...

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1 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 E) 10 NaCl mol 10 4.1 need so L 10 have but M 10 4.1 x M)(x) (1 10 1.7 : ld At thresho x 1M (aq) 2Cl (aq) Pb (s) PbCl 2 - 3 - 2 5 - - 2 2 x x x 2 Silver often appears in deposits of lead sulfide ore (galena). How might the silver be extracted? Silver and lead sulfide dissolve in nitric acid. PbS(s)+2HNO 3 (aq) Pb(NO 3 ) 2 (aq)+H 2 S(aq) K = (K sp for PbS)/(K 1 K 2 for H 2 S) Ag(s)+HNO 3 (aq) AgNO 3 (aq)+H 2 (g) G f o > 0 Ag(s)+HNO 3 (aq) AgNO 3 (aq)+NO(g)+H 2 O(l) G f o <0 Nitrates are strong electrolytes and dissociate completely in water. So we have Ag + and Pb 2+ in solution.

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2 3 Can Ag + be precipitated as AgCl (K sp = 1.8x10 -10 ) while Pb 2+ remains in solution? Consider a solution that is 1 M in Pb 2+ . The concentration of silver in galena is about 0.1%. So the concentration of Ag + in this solution is 0.001 M. We found for a solution 1 M in Pb
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## This note was uploaded on 02/13/2011 for the course CHE 132 taught by Professor Hanson during the Spring '08 term at SUNY Stony Brook.

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30 SelectivePrecip&amp;LargeK - How many moles of NaCl...

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