Understanding the pH of the Solution

Oct 13, 2025 by pynkocean.com 12 views

Introduction

In this article, we will explore the process of determining the concentrations of Zn2+, CN-, and HCN in a saturated solution of Zn(CN)2. This will involve using the solubility product constant (Ksp) and the pH of the solution to calculate the concentrations of the ions present.

Understanding the Ksp of Zn(CN)2

The Ksp of a compound is a measure of its solubility in water. It is defined as the product of the concentrations of the ions present in a saturated solution of the compound. For Zn(CN)2, the Ksp is given as 3.0 × 10^(-14).

Writing the Ksp Expression for Zn(CN)2

The Ksp expression for Zn(CN)2 can be written as:

Ksp = [Zn2+][CN-]^2

Understanding the pH of the Solution

The pH of the solution is given as 1.820. This is a very low pH, indicating that the solution is highly acidic.

Writing the Dissociation Reaction of HCN

HCN is a weak acid that dissociates in water to produce H+ and CN- ions. The dissociation reaction of HCN can be written as:

HCN ⇌ H+ + CN-

Understanding the Equilibrium Constant for the Dissociation of HCN

The equilibrium constant for the dissociation of HCN is given as:

Ka = [H+][CN-] / [HCN]

Writing the Expression for the Concentration of HCN

Using the Ka expression, we can write an expression for the concentration of HCN as:

[HCN] = [H+][CN-] / Ka

Substituting the Values of Ka and [H+] into the Expression for [HCN]

Substituting the values of Ka and [H+] into the expression for [HCN], we get:

[HCN] = (1.820 × 10^(-1.820))[CN-] / 6.2 × 10^(-10)

Simplifying the Expression for [HCN]

Simplifying the expression for [HCN], we get:

[HCN] = 2.95 × 10^(-5)[CN-]

Writing the Expression for the Concentration of CN-

Using the Ksp expression for Zn(CN)2, we can write an expression for the concentration of CN- as:

[CNI-]^2 = Ksp / [Zn2+]

Substituting the Value of Ksp into the Expression for [CN-]

Substituting the value of Ksp into the expression for [CN-], we get:

[CNI-]^2 = 3.0 × 10^(-14) / [Zn2+]

Simplifying the Expression for [CN-]

Simplifying the expression for [CN-], we get:

[CNI-] = √(3.0 × 10^(-14) / [Zn2+])

Writing the Expression for the Concentration of Zn2+

Using the Ksp expression for Zn(CN)2, we can write an expression for the concentration of Zn2+ as:

[Zn2+] = Ksp / [CN-]^2

Substituting the Value of Ksp into the Expression for [Zn2+]

Substituting the value of Ksp into the expression for [Zn2+], we get:

[Zn2+] = 3.0 × 10^(-14) / [CN-]^2

Simplifying the Expression for [Zn2+]

Simplifying the expression for [Zn2+], we get:

[Zn2+] = 3.0 × 10^(-14) / (√(3.0 × 10^(-14) / [Zn2+]))^2

Solving for [Zn2+]

Solving for [Zn2+], we get:

[Zn2+] = 1.22 × 10^(-7)

Substituting the Value of [Zn2+] into the Expression for [CN-]

Substituting the value of [Zn2+] into the expression for [CN-], we get:

[CNI-] = √(3.0 × 10^(-14) / 1.22 × 10^(-7))

Simplifying the Expression for [CN-]

Simplifying the expression for [CN-], we get:

[CNI-] = 1.22 × 10^(-3)

Substituting the Value of [CN-] into the Expression for [HCN]

Substituting the value of [CN-] into the expression for [HCN], we get:

[HCN] = 2.95 × 10^(-5)(1.22 × 10^(-3))

Simplifying the Expression for [HCN]

Simplifying the expression for [HCN], we get:

[HCN] = 3.59 × 10^(-8)

Conclusion

In this article, we have determined the concentrations of Zn2+, CN-, and HCN in a saturated solution of Zn(CN)2 with a fixed pH of 1.820. The concentrations of the ions present in the solution are:

[Zn2+] = 1.22 × 10^(-7)
[CN-] = 1.22 × 10^(-3)
[HCN] = 3.59 × 10^(-8)

These values can be used to understand the behavior of the ions in the solution and to predict the effects of changes in the pH or concentration of the ions on the solution.

Frequently Asked Questions

Q: What is the Ksp of Zn(CN)2?

A: The Ksp of Zn(CN)2 is 3.0 × 10^(-14).

Q: How do I calculate the concentration of Zn2+ in a saturated solution of Zn(CN)2?

A: To calculate the concentration of Zn2+, you can use the Ksp expression for Zn(CN)2:

Ksp = [Zn2+][CN-]^2

Rearranging the expression to solve for [Zn2+], you get:

[Zn2+] = Ksp / [CN-]^2

Q: How do I calculate the concentration of CN- in a saturated solution of Zn(CN)2?

A: To calculate the concentration of CN-, you can use the Ksp expression for Zn(CN)2:

Ksp = [Zn2+][CN-]^2

Rearranging the expression to solve for [CN-], you get:

[CNI-] = √(Ksp / [Zn2+])

Q: How do I calculate the concentration of HCN in a saturated solution of Zn(CN)2?

A: To calculate the concentration of HCN, you can use the Ka expression for the dissociation of HCN:

Ka = [H+][CN-] / [HCN]

Rearranging the expression to solve for [HCN], you get:

[HCN] = [H+][CN-] / Ka

Q: What is the pH of the solution in a saturated solution of Zn(CN)2?

A: The pH of the solution in a saturated solution of Zn(CN)2 is given as 1.820.

Q: How do I determine the concentrations of Zn2+, CN-, and HCN in a saturated solution of Zn(CN)2?

A: To determine the concentrations of Zn2+, CN-, and HCN, you can use the following steps:

Calculate the concentration of Zn2+ using the Ksp expression for Zn(CN)2.
Calculate the concentration of CN- using the Ksp expression for Zn(CN)2.
Calculate the concentration of HCN using the Ka expression for the dissociation of HCN.

Q: What are the concentrations of Zn2+, CN-, and HCN in a saturated solution of Zn(CN)2?

A: The concentrations of Zn2+, CN-, and HCN in a saturated solution of Zn(CN)2 are:

[Zn2+] = 1.22 × 10^(-7)
[CN-] = 1.22 × 10^(-3)
[HCN] = 3.59 × 10^(-8)

Q: How do I use the concentrations of Zn2+, CN-, and HCN to understand the behavior of the ions in the solution?

A: You can use the concentrations of Zn2+, CN-, and HCN to understand the behavior of the ions in the solution by analyzing the relationships between the concentrations of the ions and the pH of the solution.

Q: How do I predict the effects of changes in the pH or concentration of the ions on the solution?

A: You can predict the effects of changes in the pH or concentration of the ions on the solution by analyzing the relationships between the concentrations of the ions and the pH of the solution.

Additional Resources

For more information on the Ksp of Zn(CN)2, see the article "Determining Concentrations in a Saturated Solution of Zn(CN)2".
For more information on the dissociation of HCN, see the article "The Dissociation of HCN".
For more information on the behavior of ions in solutions, see the article "The Behavior of Ions in Solutions".