Problem: Solutions of sodium thiosulfate are used to dissolve unexposed AgBr (K sp = 5.0 X 10 -13) in the developing process for blackand- white film. What mass of AgBr can dissolve in 1.00 L of 0.500 M Na2S2O3? Ag+ reacts with S2O32- to form a complex ion:Ag+(aq) + 2S2O32-(aq) ⇌ Ag(S2O3)23-(aq)             K = 2.9 X 10 13

FREE Expert Solution

Add the two equations below: 

Eqn 1 : AgBr(s)  ⇌ Ag+(aq)   +      Br -(aq)     ;      Ksp =5.0 x 10 -13

Eqn 2 : Ag+(aq)  + 2 S2O32-(aq) ⇌  [Ag(S2O 3)2] 3-(aq)   ;      K f   = 2.9 x 10 13

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AgBr(s)   +   2 S2O 32-(aq)   ⇌  [Ag(S 2O 3) 2] 3- (aq)  +  Br -(aq) 


We added the equations and it became exactly the overall equation.

This means we can simply multiply the constants to get the overall constant. 

Keq = Ksp ×KfKeq = (5.0 × 10-13) ×(2.9 × 1013)

Keq = 14.5


'Make ICF chart: 


Take note that since the solution is only 1 L, moles and molarities can be interchangeable. 


Keq = [[Ag(S2O3)2]3-][ Br-][S2O32-]214.5 = [x][x][0.5 - 2x]214.5 = x2[0.5 - 2x]214.5 = x[0.5 - 2x]3.80789 = x[0.5 - 2x]3.80789[0.5 - 2x] =x1.90394 - 7.61578x=x1.90394=x+7.61578x1.90394=8.61578xx = 1.903948.61578

x = 0.2210 M


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Problem Details

Solutions of sodium thiosulfate are used to dissolve unexposed AgBr (K sp = 5.0 X 10 -13) in the developing process for blackand- white film. What mass of AgBr can dissolve in 1.00 L of 0.500 M Na2S2O3? Ag+ reacts with S2O32- to form a complex ion:

Ag+(aq) + 2S2O32-(aq) ⇌ Ag(S2O3)23-(aq)     

        K = 2.9 X 10 13

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