# Understanding the Constant Nature of Ksp in Solution Calculations

• kevinnn
In summary, the lab group is conducting an experiment to determine the Ksp of calcium hydroxide in pure water and in solutions of calcium chloride and potassium chloride. The teacher has stated that the Ksp for calcium hydroxide will remain constant for these solutions, and the group is asked to make a graph comparing the molar solubilities of the different solutions. The question arises as to how the Ksp can remain constant when more of one substance is forced to dissolve while less of another is forced to dissolve. The molar solubility calculation is determined by finding the calcium ion concentration in each solution and dividing it by the total volume. The experiment should be conducted under similar conditions and taking into account temperature and solvent differences.
kevinnn
My lab group and I are a bit confused. We are doing a lab where we need to calculate the Ksp of calcium hydroxide in pure water and then in different concentrations of calcium chloride and potassium chloride to analyze the diverse and common ion effect. I was absent one day but my lab partner told me that the teacher said Ksp for calcium hydroxide will remain constant for the solutions of potassium chloride and calcium chloride. She wants us to make a graph where we compare the molar solubilities of the different solutions, not the Ksp. My question is how on Earth can something that tells us about solubility, Ksp, remain constant when more is forced to dissolve, KCl, and less is forced to dissolve, CaCl2? Does this mean the molar solubility calculation is really as easy as just determining the calcium ion concentration in each solution and dividing it by the total volume? Gracias!

kevinnn said:
My lab group and I are a bit confused. We are doing a lab where we need to calculate the Ksp of calcium hydroxide in pure water and then in different concentrations of calcium chloride and potassium chloride to analyze the diverse and common ion effect. I was absent one day but my lab partner told me that the teacher said Ksp for calcium hydroxide will remain constant for the solutions of potassium chloride and calcium chloride. She wants us to make a graph where we compare the molar solubilities of the different solutions, not the Ksp. My question is how on Earth can something that tells us about solubility, Ksp, remain constant when more is forced to dissolve, KCl, and less is forced to dissolve, CaCl2? Does this mean the molar solubility calculation is really as easy as just determining the calcium ion concentration in each solution and dividing it by the total volume? Gracias!

Tell us what you exactly measure and how. Write the equation for the solubility constant What are you asked to make a graph of? If not told what seems a good idea?

Then if doing this does not already indicate to you the answers we have a chance of helping.

Last edited:
It is called a constant for a reason, because it remains constant. It will change with temperature though, pretty much everything changes with temperature, as well as with solvents and such. The numbers may also look funny if you are working at very high concentrations/ionic strengths which require the use of activities instead of molarities in equilibrium concentrations.

Assuming you performed all trials under similar conditions then, yes, you do the fairly simple calculations using the common ion effect when necessary and calculate molar solubility based on how much of the CaOH went into solution.

## 1. What is Ksp?

Ksp, or solubility product constant, is a measure of the equilibrium concentration of ions in a saturated solution of a sparingly soluble salt at a given temperature.

## 2. How do I calculate Ksp?

Ksp can be calculated by multiplying the concentrations of the ions in a saturated solution, with each concentration raised to the power of its respective stoichiometric coefficient in the dissociation equation.

## 3. What are the units of Ksp?

The units of Ksp depend on the specific salt being measured. However, they are typically expressed in units of moles per liter raised to the power of the sum of the stoichiometric coefficients in the dissociation equation.

## 4. How does temperature affect Ksp?

The solubility product constant, Ksp, is dependent on temperature. As temperature increases, Ksp generally increases as well.

## 5. Can Ksp be used to predict the solubility of a salt?

Yes, Ksp can be used to calculate the solubility of a salt. By solving for the concentration of ions in a saturated solution, the solubility of the salt can also be determined.

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