# Solubility Problem - Involves Addition of Another Ion

• vertciel
In summary, the question asks how much solid sodium fluoride needs to be added to a saturated solution of barium fluoride to increase the fluoride concentration to 3.0 x 10-2 mol/L. The solution involves using the solubility product constant for BaF2 and the initial concentrations of Ba2+ and F-. The final answer is 0.00752 M, and the correct amount needed is 1.5 x 10-2 mol.
vertciel

## Homework Statement

How many moles of solid sodium fluoride should be added to 1.0 L of a saturated solution of barium fluoride, BaF2, at 25OC to raise the fluoride concentration to 3.0 x 10-2 mol/L? The solubility product constant for BaF2 is Ksp = 1.7 x 10-6 at 25OC.

## The Attempt at a Solution

BaF2 ---> Ba2+ + 2F-

Initial Concentrations: 0, 0
Change: + x, + 2x

Therefore:

1.7 x 10-6 = x(2x)2

x = 0.00752 M.

So: [F-] = 0.01504 mol/2 L.

I thought to have the desired fluoride concentration, only 1.5 x 10-2 mol would need to be added. However, the correct answer is
2.6 x 10-2 mol
.

What happens when you add F- to the solution?

I would like to provide a response to this solubility problem. Firstly, it is important to note that the solubility product constant (Ksp) for a compound is a measure of its solubility in water, and is typically given in units of mol/L. In this problem, we are given the Ksp for barium fluoride (BaF2) at 25OC, which is 1.7 x 10-6 mol/L.

To solve this problem, we can use the equation for Ksp: Ksp = [Ba2+][F-]2. Since we are trying to raise the fluoride concentration to 3.0 x 10-2 mol/L, we can set up the following equation:

Ksp = (3.0 x 10-2 mol/L)2 = [Ba2+][F-]2

Solving for [Ba2+], we get [Ba2+] = Ksp/[F-]2 = (1.7 x 10-6 mol/L)/[3.0 x 10-2 mol/L]2 = 0.0019 mol/L.

Since we are starting with a saturated solution of barium fluoride (BaF2), we know that the concentration of [Ba2+] is already at its maximum solubility. Therefore, to increase the fluoride concentration to 3.0 x 10-2 mol/L, we need to add more fluoride ions (F-).

The amount of solid sodium fluoride (NaF) needed can be calculated by using the equation: [F-] = [NaF] = moles of NaF/volume of solution.

Therefore, [NaF] = (3.0 x 10-2 mol/L) - (0.0019 mol/L) = 0.0281 mol/L.

Since we are working with a 1.0 L solution, the moles of NaF needed can be calculated as:

moles of NaF = (0.0281 mol/L)(1.0 L) = 0.0281 mol.

Therefore, 0.0281 mol of solid sodium fluoride should be added to 1.0 L of the saturated solution of barium fluoride to achieve a fluoride concentration of 3.0 x 10-2 mol/L.

In summary, the key to solving this problem is to recognize that the solubility product

## 1. What is the definition of solubility?

Solubility refers to the ability of a substance to dissolve in a solvent, resulting in a homogenous mixture.

## 2. How does the addition of another ion affect solubility?

The addition of another ion can either increase or decrease solubility, depending on the type of ions present. For example, adding a common ion, such as sodium chloride, can decrease the solubility of a substance, while adding a complexing ion, such as ammonia, can increase solubility.

## 3. Why is it important to understand solubility problems involving the addition of another ion?

Understanding solubility problems involving the addition of another ion is important for many scientific fields, such as chemistry, biology, and environmental science. It allows researchers to predict the behavior of substances in different environments and to design experiments accordingly.

## 4. What factors influence the solubility of a substance?

The solubility of a substance is influenced by several factors, including temperature, pressure, the nature of the solvent and solute, and the presence of other substances, such as ions or gases.

## 5. How can one calculate the solubility of a substance in the presence of another ion?

To calculate the solubility of a substance in the presence of another ion, one can use the common ion effect equation, which takes into account the initial solubility of the substance, the concentration of the added ion, and the solubility product constant (Ksp) of the substance.

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