- #1

leena19

- 186

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## Homework Statement

The k

_{sp}values of AgCl and Ag

_{2}CrO

_{4}are 2*10

^{-10}mol

^{2}dm

^{-6}and 3*10

^{-12}mol

^{3}dm

^{-9}respectively.100cm

^{3}of an aqueous solution contains NaCl and K

_{2}CrO

_{4}only,whose cocentrations are 0.1M and 0.1M respectively.To this solution,is added AgNO

_{3}dropwise while mixing.

(1) Calculate and show whether AgCl or Ag

_{2}CrO

_{4}will be precipitated first?

(2) When the second precipitate begins to appear,what is the concentration of the anion of the Ag salt that precipitated first ,which still remains in the solution?

(3) Using the above answer,explain briefly the accuracy of K

_{2}CrO

_{4}as an indicator when used in the above titration.

## Homework Equations

## The Attempt at a Solution

I managed to do part (1) of the problem but m having trouble with the rest

For(1),

AgNO

_{3}[tex]\rightarrow[/tex] Ag

^{+}+NO

_{3}

^{-}

AgCl [tex]\rightarrow[/tex] Ag

^{+}+ Cl

^{-}

Ksp = [ Ag

^{+}] [Cl

^{-}]

2*10

^{-10}/0.1 = [ Ag

^{+}]

[ Ag

^{+}]=2*10

^{-9}M

Ag

_{2}CrO

_{4}[tex]\rightarrow[/tex]2Ag

^{+}+ CrO

_{42-}

Ksp= [Ag

^{+}]

^{2}[CrO

_{42-}]

3*10

^{-12}/0.1 = [Ag

^{+}]

^{2}

[Ag

^{+}] = 5.477*10

^{-6}M

since the minimum concentration of Ag+ needed to precipitate AgCl is less than that needed to precipitate Ag chromate,AgCl would precipitate 1st.

(2) I'm not sure I understand the question,

which means the [Ag+] present in the solution is now, 5.477*10When the second precipitate begins to appear

^{-6}M,right? but what do I do now?Do I just substitute this value to the ksp equation of AgCl and find the[chloride] in the precipitate and then substract this value from 0.1M?

THANK YOU.