A 75 L solution of 0.63 M Fe(NO3)3 is mixed with 89 mL of 0.33 M Ni(NO3)2. Ksp F

Question

A 75 L solution of 0.63 M Fe(NO3)3 is mixed with 89 mL of 0.33 M Ni(NO3)2. Ksp Fe(OH)3=1.63x10^-39 and Ksp Ni(OH)2 = 6x10^-16

(a) If solid KOH is added to the solution, what will precipitate first? Give the chemical formula.

(b) If solid KOH is added to the solution, at what concentration of [OH-] will one begin to see the first sign of precipitate?

(c) At what concentration of [OH-] will one begin to see the first sign of precipitation of the second complex?

(d) What is the chemical formula for this second substance precipitating?

Explanation / Answer

My answer is,

a. If solid KOH is added to a mixture of 75 L of 0.63M of Fe(NO3)3 and 85 mL of 0.33M of Ni(NO3)2, then, Fe(OH)3 will precipitate out first as it is more saturated.

b. The concentration of [OH-] at which the first precipitate occurs

     1.63 x 10-39 = X x 0.63 M

      X = 2.587 x 10-39 M

c. The concentration of [OH-] at which the second precipitation occurs

    6 x 10-16 = X x 0.33M

      X = 18.18 x 10-16 M

d. Chemical formula for second substance precipitating is Ni(OH)2.

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