We will subtract x, we will add x.

And we will be left with 0.249 minus x, x, and x.

Since this is an equilibrium of a weak acid, we know that Ka is equal

to the A- concentration times the H3O+ concentration, divided by the HA.

That doesn't look like an H, HA concentration.

And we can plug the values in that we know.

Ka is given up there as 1.54 times 10 to the -5.

And that is going to be equal to x times x, or

x squared, divided by 0.249 minus x.

Because Ka is small, at this point we can ignore this x term or at least try to,

and multiply both sides by 0.249 to get it off the denominator.

This will give me 1.54 times 10 to the -5,

times 0.249, equal to x squared.

When I multiply this two values, and also take the square root,

I will obtain a value for x of 1.96 times 10 to the -3.

And this is a very small number compared to that, so

it is a legitimate assumption that we made.

You could take this value divided by this value, okay.

This number here divided by this number, and

you would see that it is less than 5% of that value.