Question

What is the [Tl3+] in a solution that is buffered at pH 11.50 at 25 °C? The Ksp of Tl(OH)3 is 2 × 10–44 at 25 °C.

6.33 × 10–10 mol/L

6.33 × 10–33 mol/L

6.33 × 10–37 mol/L

6.33 × 10–12 mol/L

Answer 1

To solve this problem, we'll use the solubility product constant (Ksp) expression for Tl(OH)3:

Ksp = [Tl^3+][OH^-]^3

We're given that the solution is buffered at pH 11.50, which means that the hydroxide ion concentration ([OH^-]) is known. At pH 11.50, the concentration of hydroxide ions can be calculated using the formula:

pOH = 14 - pH

pOH = 14 - 11.50 = 2.50

Now, convert pOH to [OH^-] using the formula:

[OH^-] = 10^(-pOH)

[OH^-] = 10^(-2.50) = 3.16 × 10^(-3) mol/L

Now we can use the Ksp expression to find the concentration of [Tl^3+]:

Ksp = [Tl^3+][OH^-]^3

2 × 10^(-44) = [Tl^3+][(3.16 × 10^(-3))^3]

Solve for [Tl^3+]:

[Tl^3+] = (2 × 10^(-44)) / (3.16 × 10^(-9))

[Tl^3+] ≈ 6.33 × 10^(-37) mol/L

Therefore, the correct answer is: 6.33 × 10^(-37) mol/L.