After the solution reaches equilibrium, what concentration of Ag+ (aq) remains
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After the solution reaches equilibrium, what concentration of Ag+ (aq) remains

[From: ] [author: ] [Date: 12-03-31] [Hit: ]
0 mLsample of a solution that is 0.14 Min NaCN. Ag+ concentration?Ag+=(.125L*2.7e-3)/(.......
A 125.0 mL sample of a solution that is 2.7×10−3 M in AgNO3 is mixed with a 230.0 mL sample of a solution that is 0.14 M in NaCN. Ag+ concentration?

Attempt:

Ag+=(.125L*2.7e-3)/(.23L+.125L)=9.51e-…

Ice table
Ag CN Ag(CN)2
I 2.7e-3 .14 0
C 2.7e-3 2(2.73-3) 2.7e-3
E -x .1346 2.7e-3

Kf (1e21)=(2.7e-3)/x(.1346)^2 x=1.49e-22
What am I doing wrong?

-
125.0 mL sample of a solution that is 2.7×10−3 M in AgNO3 is
(0.125 L ) (2.7×10−3 mol / L) = 0.0003375 moles of Ag+



230.0 mL sample of a solution that is 0.14 M in NaCN is
(0.230 L) (0.14 M in NaCN) = 0.0322 moles of CN-

========================

when 0.0003375 moles of Ag+ is mixed with 0.0322 moles of CN-
we say that essentially all of the 0.0003375 moles of Ag+ is converted to [Ag(CN)2]^-1

the 0.0003375 moles of [Ag(CN)2]^-1 has been diluted to a total volume of 355.0 ml:
(0.0003375 moles of [Ag(CN)2]^-1) / (0.3550L) = 0.000951 Molar [Ag(CN)2]^-
(& you got that as 9.51e-4)


======================================…

by the equation:
1 Ag+ & 2 CN-1 --> [Ag+(CN-)2]^-1
twice as much CN- is consumed, when it reacts with the 0.0003375 moles of Ag+:
(0.0322 moles of CN-) - (2) (0.0003375 moles lost) = 0.031525 mol CN- remains

which has also been diluted to 355.0 ml
(0.031525 mol CN- remains) / (0.355L) = 0.0888 Molar CN-

================================

Kf = [Ag+(CN-)2] / [Ag+] [CN-]^2

1 X 10^21 = [0.000951] / [Ag+] [0.0888]^2

[Ag+] = [0.000951] / (1 X 10^21 ) [0.0888]^2

[Ag+] = [0.000951] / (1 X 10^21 ) (0.007885)

Ag = 1.2 X 10^-22 Molar


however you might be expected to round that off to Ag = 1 X 10^-22 Molar
(since the Kf had only one sig fig showing in its 1e21)
1
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