**Ouch, that hurts!**

Bees are beautiful creatures that help plants flourish. They carry pollen from one plant to another to facilitate plant growth and development. But, they can also be troublesome when they sting you. For people who are allergic to bee venom, this can be a serious, life-threatening problem. For the rest of us, it can be a painful experience. When stung by a bee, one first-aid treatment is to apply a paste of baking soda (sodium bicarbonate) to the stung area. This weak base helps with the itching and swelling that accompanies the bee sting.

### Calculating pH of Weak Acid and Base Solutions

The

#### Sample Problem: Calculating the pH of a Weak Acid

Calculate the pH of a 2.00 M solution of nitrous acid (HNO_{2}). The ^{-4}.

*Step 1: List the known values and plan the problem.*

Known

- initial [HNO
_{2}] = 2.00 M Ka=4.5×10−4

Unknown

- pH = ?

First, an ICE table is set up with the variable

*Step 2: Solve.*

Concentrations |
[HNO_{2}] |
[H^{+}] |
[NO_{2}^{−}] |

Initial | 2.00 | 0 | 0 |

Change | |||

Equilibrium |

The

The quadratic equation is required to solve this equation for

Since the variable

*Step 3: Think about your result.*

The pH of a 2.00 M solution of a strong acid would be equal to

The procedure for calculating the pH of a solution of a weak base is similar to that of the weak acid in the sample problem. However, the variable

### Review

- What does
x stand for in the equation? - What simplifying assumption is made?
- What would
x stand for if we were calculating pOH?