Titration is the chemistry equivalent of a measuring stick--a way to measure the concentration of an unknown chemical in a sample. When performing titrations, the titrant is the substance added to neutralize the chemical in the sample, which is called the analyte. The equivalence point is the point at which all of the chemical in the analyte has been neutralized. Problems on general chemistry tests will sometimes ask you to find the amount of titrant needed to reach the equivalence point and pH at equivalence.
Determine the number of moles of acid or base originally present in the analyte. If you're working a problem on a chemistry exam, this value will usually be given to you, although you may need to convert from concentration to number of moles. The simplest way to do so is to multiply the concentration by the number of liters of analyte you have. If you're working with a sample in the lab, on the other hand, you may need to do a titration experiment first.
Write down the chemical equation for the reaction between the analyte and the titrant. Note the ratio between the reactants--is it one-to-one, or do you need two or three molecules of one reactant for every molecule of the other?
Use the ratio of the reactants to calculate how much titrant is needed to neutralize the analyte. If you need two molecules of titrant for every molecule of analyte, for example, the number of moles of titrant you need is equal to two times the number of moles of analyte.
Divide the number of moles of titrant you need by the concentration of the titrant (its molarity) to find the volume of titrant needed to reach the equivalence point. This may be all you need; if the problem asks you to find the pH at equivalence, however, you have several more steps to complete.
Determine whether the analyte is a strong or weak acid or base. The titrant will nearly always be a strong acid or base, because it's more difficult to determine the equivalence point if a weak acid or base is used as the titrant instead. If the analyte is a strong acid or base, the pH at equivalence will be 7. If it is not, however, you'll need to perform another step.
Determine whether the salt produced by the neutralization reaction is acidic or basic. A strong base added to a weak acid will produce a weakly basic salt; a strong acid added to a weak basic will produce a weakly acidic salt. Now identify the salt produced by the reaction using the chemical equation you wrote in step 2. The amount of the salt present at equivalence will be equal to the number of moles of acid or base originally present in the analyte.
Use the equilibrium constant equation to find the concentration of hydronium or hydroxide ions at equivalence. The Ka or Kb for the acidic salt or base will usually be given to you on an exam; you can convert from Ka to Kb using the equation (Ka)(Kb) = Kw, where Kw is 1x10 to the -14, the autoprotolysis constant of water. The equilibrium constant equation for a weak acid or base is as follows: Ka = x squared / a, where a is the concentration of the acidic salt or base at equivalence.
Take the negative log of the hydronium ion concentration (if the salt is a weak acid) to find the pH. If the salt is a weak base, take the negative log of the hydroxide ion concentration and subtract it from 14 to find the pH.
If you're looking at a graph of pH values during a titration, the curve will typically have a sigmoid shape (more or less) if the acid or base in the analyte is monoprotic. The equivalence point is midway up the steep part or "cliff" on the curve.