a. Calculate the pH at which Aluminum Hydroxide just starts to precipitate from

Question

a. Calculate the pH at which Aluminum Hydroxide just starts to precipitate from a 0.00066 M solution of Aluminum nitrate. Ksp for aluminum hydroxide = 3.0 X 10-34

b. A 3.07 X 10-6 M solution of Nickel (II) Chloride is saturated with H2S at a pH = 5.61. What is the Qsp at the point of mixing? Hint: the Qsp will come from the solubility equilibrium of the precipitate that forms in this solution. Decide what the insoluble product would be and work from there. Remember that Kaoverallfor H2S = 1.3 X 10-20 and that a saturated solution of H2S = 0.10 M.

Explanation / Answer

a) Consider the dissociation of aluminum hydroxide, Al(OH)3 as below.

Al (OH)3 (s) <======> Al3+ (aq) + 3 OH- (aq)

The solubility product constant is given as

Ksp = [Al3+][OH-]3

We have 0.00066 M aluminum nitrate, Al(NO3)3; therefore, [Al3+] = 0.00066 M.

Plug in the expression for Ksp and get

Ksp = (0.00066)*[OH-]3

=====> 3.0*10-34 = (0.00066)*[OH-]3

=====> [OH-]3 = (3.0*10-34)/(0.00066) = 4.54*10-31

=====> [OH-] = 7.68*10-11

Therefore, we have [OH-] = 7.68*10-11 M and pOH = -log [OH-] = -log (7.68*10-11) = 10.11

Therefore, the desired pH is pH = 14 – pOH = 14 – 10.11 = 3.89 (ans).

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.