Kaplan Solubility Problem

[axp107]

Q about solubility..

If 1 ml of 1E-5 M NaSCN solution is added to 3 ml of a 1E-5 M AgNO3 solution, will there be any precipitate?

Ksp values

AgSCN : 1E-12
AgCl: 1.8E-10


How would you approach this problem? Whenever you mix more than 1 thing in a solution, I always get confused.

Heres what I have so far.. you can find the moles of NaSCN and moles of AgNO3

Then

NaSCN --> Na+ +SCN-
AgNO3 --> Ag+ + NO3-

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[sehnsucht]

Q about solubility..

If 1 ml of 1E-5 M NaSCN solution is added to 3 ml of a 1E-5 M AgNO3 solution, will there be any precipitate?

Ksp values

AgSCN : 1E-12
AgCl: 1.8E-10


How would you approach this problem? Whenever you mix more than 1 thing in a solution, I always get confused.

Heres what I have so far.. you can find the moles of NaSCN and moles of AgNO3

Then

NaSCN --> Na+ +SCN-
AgNO3 --> Ag+ + NO3-

Based on the KSP, both products are very insoluble in water (big Ksp=soluble in water, small Ksp=not soluble in water). From experience, I know that AgCl is not very soluble in water at all and it doesn't take much of it to saturate a solution. I've never worked with silver thiocyanate before but I would imagine it doesn't go into solution very well like AgCl.

 

[dshnay]

Here's what I did.
1. Find the amount of moles of each substance mmol = M * ml
2. Find the new molarity. M = mmol/(total new vol 1 + 3 ml)
you should come up with 2.5*10^-6 for NaScn and 7.5e-6 for AgNO3
3. Ksp = 1e-12 = [Ag][SCN] same thing as 1e-12=X^2
X= 1e-6

So you need that much of each product for precipation to form. You have more then that so you should see it precip

 

[artaxerxes]

what does AgCl's ksp have anything to do withanything?

if AgNO3's ksp is less than AgSCN, it will be the percipitate, but the way the question is asked, I guess its assumed that AgNO3 is dissolved.

 

[EECStoMed]

When I look at this problem I 1st look into my brain and see what's soluble and what's not. AgNO3 is soluble because it was a NO3 group, NaSCN is soluble because it was an alkali metal group. So then we do the pairing thing, NaNO3 is clearly soluble and then of course we have AgSCN which OF COURSE is insoluble because Ag is insoluble with anything other than NO3-, ClO4- and C2H3O2-<- gotten from TPR book. So from that I know that AgSCN will precipitate; not only that but looking from the KSP values, I know that AgCl is NOT soluble because Ag is paired with Cl- and not the 3 above which I stated it would be soluble with, the fact that AgSCN has an even smaller Ksp reassures me that my above answer is correct.

Q about solubility..

If 1 ml of 1E-5 M NaSCN solution is added to 3 ml of a 1E-5 M AgNO3 solution, will there be any precipitate?

Ksp values

AgSCN : 1E-12
AgCl: 1.8E-10


How would you approach this problem? Whenever you mix more than 1 thing in a solution, I always get confused.

Heres what I have so far.. you can find the moles of NaSCN and moles of AgNO3

Then

NaSCN --> Na+ +SCN-
AgNO3 --> Ag+ + NO3-