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Calculate Ph of 10m Hcn That Is 0.007 Ionized

Reviewed by Calculator Editorial Team

This calculator determines the pH of a 10m HCN solution where 0.007 of the HCN is ionized. The calculation accounts for the weak acid properties of hydrogen cyanide and provides the exact pH value along with an explanation of the chemical equilibrium involved.

Introduction

Hydrogen cyanide (HCN) is a weak acid that partially dissociates in water according to the equilibrium reaction:

Dissociation Reaction

HCN + H2O ⇌ H3O+ + CN-

The pH of a solution containing HCN depends on the concentration of the HCN and the degree of ionization. This calculator specifically addresses the scenario where a 10m (0.01 molar) HCN solution has 0.007 of its HCN molecules ionized.

pH Calculation

The pH of the solution can be calculated using the following steps:

  1. Determine the concentration of hydronium ions (H3O+) based on the ionization degree.
  2. Calculate the pH from the hydronium ion concentration.

pH Calculation Formula

pH = -log[H3O+]

Where [H3O+] is the concentration of hydronium ions in moles per liter.

In this specific case, the ionization degree is 0.007, meaning 0.7% of the HCN molecules are dissociated. For a 0.01 M solution, this results in:

Hydronium Ion Concentration

[H3O+] = 0.007 × 0.01 M = 7 × 10-5 M

Using this concentration in the pH formula gives the result shown in the calculator.

Worked Example

Let's walk through the calculation for a 10m HCN solution where 0.007 of the HCN is ionized:

  1. Initial HCN concentration: 0.01 M (10m)
  2. Ionization degree: 0.007 (7%)
  3. Hydronium ion concentration: 0.007 × 0.01 = 7 × 10-5 M
  4. pH = -log(7 × 10-5) ≈ 4.15

This means the pH of the solution is approximately 4.15, indicating it is slightly acidic.

FAQ

What does it mean when 0.007 of HCN is ionized?

An ionization degree of 0.007 means that 0.7% of the HCN molecules in the solution have dissociated into H3O+ and CN- ions. This affects the pH of the solution.

How does the concentration of HCN affect the pH?

The pH depends on both the concentration of HCN and the degree of ionization. Higher concentrations or higher ionization degrees will result in lower pH values (more acidic solutions).

Can this calculator be used for other weak acids?

This calculator is specifically designed for HCN solutions. For other weak acids, you would need a different calculator that accounts for their specific dissociation constants.