# If a buffer solution is prepared from 5.15g #NH_4NO_3# and 0.10L of 0.15M #NH_3#, what is the pH of the solution?

##### 2 Answers

#### Explanation:

It can be shown relatively easily that the

You have not quoted

Given the

Note that here I knew that volume of the solution was

PS I hope you can see the units in my calculations, because I can't! It is important that the dimensions in the log argument cancel out, which I think they do!

#### Explanation:

The ammonium ion is a weak acid and dissociates:

For which:

To find the

Rearranging gives:

These are all **equilibrium** concentrations. We can set up an

For the initial moles of

The initial moles of

From the formula we can see that the initial moles of

Now we can set up the

Because the value of

and

Now we can put the numbers into

You will note I can use moles and not concentrations as the volume is common to both

This also accounts for any volume change when the solid salt is added to the solution.

In practice you could go straight to

This only works if