# How would you use the Henderson-Hasselbalch equation to calculate the pH of a solution that is 0.120 M in HClO and 0.185 M in KClO?

##### 1 Answer

#### Explanation:

The **Henderson - Hasselbalch equation** allows you to calculate the pH of buffer solution that contains a weak acid and its conjugate base by using the concentrations of these two species and the

#color(blue)("pH" = pK_a + log( (["conjugate base"])/(["weak acid"])))#

In your case, the weak acid is *hypochlorous acid*, *hypochlorite anion*,

The *acid dissociation constant*,

Now, before doing any calculations, try to predict what you expect the solution's pH to be *compared with* the acid's

Notice that when you have **equal concentrations** of weak acid and conjugate base, the log term will be equal to **zero**, since

#log(1) = 0#

This tells you that if you have **more conjugate base** than weak acid, the log term will be *greater than* **higher** than the

With this in mind, plug in your values into the H-H equation to get

#"pH" = -log(3.5 * 10^(-8)) + log( (0.185color(red)(cancel(color(black)("M"))))/(0.120color(red)(cancel(color(black)("M")))))#

#"pH" = 7.46 + 0.188 = color(green)(7.65)#