04-12-2018, 04:39 AM

HI!!

I don't understand how to calculate pH and [Ag+] of a solution of:

NH3 0,10M

AgNO3 10-2M

(pkb NH3 =4.7 , logK1=3.32, logK2 =3.89 )

K1 -----> Ag++ NH3 >>> [AgNH3]+

K2 -----> Ag+ + AgNH3+ >>> Ag(NH3)2 +

I should use the two "mass" balance of the ligand NH3 and [Ag+] :

CNH3= [NH3] + [NH4+] + [AgNH3]+ + 2[ Ag(NH3)2 +]

CAg+ = [Ag+] + [AgNH3+] + [ Ag(NH3)2 +]

Then i know this formula:

β' = β*αNH3 acid/base

[NH3']= [NH3] + [NH4+] (the not-complexated ligand)

[Ag+] = CAg+ * 1/(1+β'[NH3'] + β'[NH3']2) ≈CAg+ * 1/( β'[NH3']2)

But my problem now is to calculate the value of [NH3] because it's a funciotn of pH,but also of the complex equilibrium (i don't have the pH fixed/set)

Usually i use this relation (when i don't have competitive equilibrium):

Cligand - [L] = nCmetal - n[M]

And put it in:

[M]= CM* 1/ β[L]n (i suppose that βn >> βi ...with i=1,2...n-1)

And i solve this for [M]^2...

But now i have also an acid base equilibrium and i think it's not corret...: (i have β' and [L'] and not only β, [L] )

Some help??

Thanks

I don't understand how to calculate pH and [Ag+] of a solution of:

NH3 0,10M

AgNO3 10-2M

(pkb NH3 =4.7 , logK1=3.32, logK2 =3.89 )

K1 -----> Ag++ NH3 >>> [AgNH3]+

K2 -----> Ag+ + AgNH3+ >>> Ag(NH3)2 +

I should use the two "mass" balance of the ligand NH3 and [Ag+] :

CNH3= [NH3] + [NH4+] + [AgNH3]+ + 2[ Ag(NH3)2 +]

CAg+ = [Ag+] + [AgNH3+] + [ Ag(NH3)2 +]

Then i know this formula:

β' = β*αNH3 acid/base

[NH3']= [NH3] + [NH4+] (the not-complexated ligand)

[Ag+] = CAg+ * 1/(1+β'[NH3'] + β'[NH3']2) ≈CAg+ * 1/( β'[NH3']2)

But my problem now is to calculate the value of [NH3] because it's a funciotn of pH,but also of the complex equilibrium (i don't have the pH fixed/set)

Usually i use this relation (when i don't have competitive equilibrium):

Cligand - [L] = nCmetal - n[M]

And put it in:

[M]= CM* 1/ β[L]n (i suppose that βn >> βi ...with i=1,2...n-1)

And i solve this for [M]^2...

But now i have also an acid base equilibrium and i think it's not corret...: (i have β' and [L'] and not only β, [L] )

Some help??

Thanks