Solubility of Cr hydroxide in buffered solution

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In summary, the solubility of Cr(OH)3 in a solution buffered at pH = 8.673 can be calculated by using the Ksp expression and the concentration of [OH-] obtained from the buffer pH. From the resulting [Cr+3] concentration, the amount of grams of Cr(OH)3 that will produce that concentration can be determined.
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tiggrulz13
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Homework Statement


What is the solubility (gram/liter) of Cr(OH)3 (103.02 g/mol) in a solution buffered at pH = 8.673? The pKsp of Cr(OH)3 is 30.220.


Homework Equations


Ksp = [Cr][OH]^3
Cr(OH)3 -> Cr + 3OH


The Attempt at a Solution


I have already solved that Ksp = 6.0256 E -31, but I'm not entirely sure what to do with the buffer pH. I tried using it to find the pOH and subsequently [OH], but for some reason I'm not getting the right answer. Do I plug [OH] into the Ksp equation after finding out the concentration using the pH or is there a step I'm missing?
 
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  • #2
Sounds like you are approaching it correctly. Use the concentration of [OH-] you obtain from the pOH in the Ksp expression and determine [Cr+3]. From that revelation back out how many grams of Cr(OH)3 will produce that concentration of [Cr+3].
 
  • #3


The buffer pH will affect the solubility of Cr(OH)3 in the solution. A buffer solution helps to maintain a constant pH by resisting changes in the concentration of hydrogen ions. In this case, the buffer at pH 8.673 will contain a significant amount of hydroxide ions (OH-) which will compete with the Cr(OH)3 for binding sites and decrease its solubility.

To incorporate the effect of the buffer pH, you can use the Henderson-Hasselbalch equation: pH = pKa + log([A-]/[HA]), where [A-] is the concentration of the conjugate base (OH-) and [HA] is the concentration of the weak acid (Cr(OH)3). Rearranging this equation, we get [A-]/[HA] = 10^(pH-pKa).

In this case, the pKa of Cr(OH)3 is 30.220, so [A-]/[HA] = 10^(8.673-30.220) = 1.39 x 10^-22. This means that for every 1 molecule of Cr(OH)3, there will be 1.39 x 10^-22 molecules of OH-.

Now, using the Ksp equation: Ksp = [Cr][OH]^3, we can substitute the [OH] value we just found to get Ksp = [Cr](1.39 x 10^-22)^3. Solving for [Cr], we get [Cr] = Ksp/(1.39 x 10^-22)^3 = 3.85 x 10^-87 M.

To convert this to grams per liter, we multiply by the molar mass of Cr(OH)3 (103.02 g/mol) and by the conversion factor 1000 mL/L to get 3.97 x 10^-84 g/L. This is the solubility of Cr(OH)3 in the buffered solution at pH 8.673.

It is important to note that this is a very low solubility, which is expected for a compound with a very small Ksp value. This means that only a very small amount of Cr(OH)3 will dissolve in the buffered solution at this pH.
 

1. What is the solubility of Cr hydroxide in buffered solution?

The solubility of Cr hydroxide in buffered solution can vary depending on the pH of the solution and the type of buffer used. Generally, it has a low solubility in acidic solutions and a higher solubility in basic solutions.

2. How does the presence of a buffer affect the solubility of Cr hydroxide?

A buffer can affect the solubility of Cr hydroxide by maintaining a constant pH in the solution. This can help to keep the concentration of hydroxide ions, which play a role in the solubility of Cr hydroxide, constant and thus affect its solubility.

3. Can the solubility of Cr hydroxide be manipulated in a buffered solution?

Yes, the solubility of Cr hydroxide can be manipulated in a buffered solution by adjusting the pH of the solution. This can be done by adding an acidic or basic solution to the buffer to shift the equilibrium and change the solubility of Cr hydroxide.

4. What is the significance of studying the solubility of Cr hydroxide in buffered solution?

Studying the solubility of Cr hydroxide in buffered solution is important in understanding the behavior of this compound in different environmental and chemical conditions. This information can be applied in various fields such as water treatment, industrial processes, and environmental remediation.

5. Are there any factors that can affect the solubility of Cr hydroxide in a buffered solution?

Yes, besides pH and buffer type, other factors that can affect the solubility of Cr hydroxide in a buffered solution include temperature, ionic strength, and the presence of other ions or compounds that can interact with the Cr hydroxide.

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