[bakerbg]

Hello Guys!!

I got this question in class:

Given that the solubility product value (Ksp) of AgCl is 1.8 X 10[-10], will a precipitate form when 1cm[3] of 0.001M AgNO[3] is added to 1dm[3] of 0.001M NaCl?

I say NO. From the solubilty product value of AgCl, the solubility of AgCl is:

1.8 X 10[-10] = [Ag

• X [ Cl[-] i therefore found the square root of 1.8 X 10[-10] which gives the solubility of AgCl as 1.34 X 10[-5]moles per dm[3]

Now, how much Ag

• do we have in 1 cm[3] of 0.001M AgNO[3]?

since 1000 cm[3] AgNO[3] contains 0.001 moles
then  1 cm[3]  AgNO[3] will contain   1 / 1000 X 0.001
                                                 = 1.0 X 10[-6] moles  [Ag

• ions

if this amount of [Ag

• is place in the 1 dm[3] of NaCl - assuming there is no change in volume - then the new concentration of [Ag
• is 1.0 X 10[-6] moles per dm[3].

I therefore say: since the new concentration of Ag

• is less than the solubility of AgCl - then [NO PRECIPITATE WILL BE FORMED].

Am I right? My teacher and classmates don't think so.

[rabolisk]

Does the Cl- matter at all?

[bakerbg]

excellent point!!

I reasoned that the Cl^- is in excess while the Ag^{+ is the limited reagent. Since Ag+ combine with Cl- in a 1:1 mole ratio , only the same amount of Ag+ as Cl- can combine to form AgCl .the rest of Cl- will remain as spectators!! and there certainly is not enough Ag+ to form a precipitate!}

[rabolisk]

What you are saying is that the solubility of AgCl is determined by the limiting ion only, whether that is Ag+ or Cl-. Go back to what Ksp means and see if this makes sense.

[bakerbg]

You are absolutely right. It is incorrect to determine the solubility from just the concentration of Ag+ in this one instance. what I should have said is that that amount of Ag⁺ is in solution - which is below the solubility value of AgCl.

[rabolisk]

Solubility of AgCl (the amount of AgCl that dissolves in a given volume) is not a constant value. What is constant is Ksp. In short, you are wrong, and your teacher is correct.

[bakerbg]

Thank you Rabolisk