An acid-base titration is a neutralization reaction performed in the lab to determine an unknown concentration of acid or base. The moles of acid will equal the moles of the base at the equivalence point. So, if you know one value, you automatically know the other. Here's how to perform the calculation to find your unknown:

### Acid-Base Titration Problem

If you're titrating hydrochloric acid with sodium hydroxide, the equation is:

HCl + NaOH → NaCl + H_{2}O

You can see from the equation there is a 1:1 molar ratio between HCl and NaOH. If you know that titrating 50.00 ml of an HCl solution requires 25.00 ml of 1.00 M NaOH, you can calculate the concentration of hydrochloric acid, HCl. Based on the molar ratio between HCl and NaOH, you know that at the equivalence point:

moles HCl = moles NaOH

### Acid-Base Titration Solution

Molarity (M) is moles per liter of solution, so you can rewrite the equation to account for molarity and volume:

M_{HCl} x volume_{HCl} = M_{NaOH} x volume_{NaOH}

Rearrange the equation to isolate the unknown value. In this case, you are looking for the concentration of hydrochloric acid (its molarity):

M_{HCl} = M_{NaOH} x volume_{NaOH} / volume_{HCl}

Now, simply plug in the known values to solve for the unknown:

M_{HCl} = 25.00 ml x 1.00 M / 50.00 ml

M_{HCl} = 0.50 M HCl