**Weak Acid Dissociation**

Weak acids can dissociate in an aqueous solution to achieve equilibrium. The **percent dissociation** is defined as follows:

Percent dissociation = amount dissociated (mol/L) / initial concentration (mol/L) x 100%

For example,

HC_{2}H_{3}O_{2} (aq) = H^{+} (aq) + C_{2}H_{3}O_{2}^{-} (aq)

The equilibrium expression is

K_{a} = 1.8 x 10^{-5} = [H^{+}][C_{2}H_{3}O_{2}^{-}] / [HC_{2}H_{3}O_{2}]

The **percent dissociation** can be calculated as:

**Percent dissociation** = [H^{+}] (final) / [HC_{2}H_{3}O_{2}] (initial)

*This module can perform the following calculations:*

*1. Known initial concentration of a weak acid and Ka, calculate percent dissociation and pH.*

*2. Known initial concentration of a weak acid and percent dissociation, calculate Ka and pH.*

*3. Known initial concentration of a weak base and Kb, calculate pH.*

*E**xample,*

*For acetic acid with the initial concentration of 1.00M, K _{a} = 1.8 x 10^{-5}*

This is one step process, enter the known data and press **Calculate** to output the unknowns.

1. Select **Weak Acid Dissociation** link from the front page or **Weak Acid dissociation** tab from the **Acid****, Base****and Salt** module. The Input and Output screen appears.

2. In the **Input** area, enter the known quantities with a proper significant figure.

3. Click **Calculate** to output the answer.

4. The **Show Work** area on the right shows you step-by-step how your problem has been solved.

To start a new problem, click **Reset**. All Input fields will be cleared. Follow Step 1-3 again.