Titration is an analytical method in which a standard solution is used to determine the concentration of another solution.

Any solution for which the concentration is precisely known is called a standard solution.

An acid/base titration uses the fact that one can be "neutralized" with the other. In a neutralization reaction, the acid and base will combine to produce a salt plus water. When done correctly, the resulting solution will be "neutral" - neither acid nor base. This is known as the end point of the titration. The change in pH of the solution can be monitored using an indicator or pH meter. It is extremely important that the amounts of each solution used to reach the end point are measured exactly .

NaOH + HCl  →  NaCl + H₂O

The balanced neutralization equation above indicates that 1 mole of sodium hydroxide will combine with 1 mole of hydrochloric acid to produce 1 mole of sodium chloride and 1 mole of water.

	This graph represents the titration of 10 ml of 0.1M HCl with 0.1M NaOH. The end point is represented on the graph by a rapid change in pH with very little base added. The end point is recognized in the solution when the phenolphthalein holds its faint pink color, as shown in the drawing on the right.

Phenolphthalein is a common indicator used in acid/base titrations. Two or three drops are added to the solution to be titrated. The titration can begin with either an acidic or basic solution. It is somewhat easier to see the early color changes when starting with an acidic solution. The acidic solution will be colorless when the phenolphthalein is added. Slowly add the base solution until the faint pink color persists for at least 10 seconds. At the end point, the concentration of the standard and the volume used is known, as well as the volume of the unknown used. Calculations can now be done to compare the number of moles of each solution used. This will give the concentration of the unknown. Use this webpage to perform a virtual titration.	Phenolphthalein Color Change acidic solution
	neutral solution
	basic solution

 

Sample titration problem and solution:

What is the molarity of an NaOH solution if 48.0 ml is needed to neutralize 35.0 ml of 0.144 M H₂SO₄?

1. Write a balanced quation for the reaction.

   H₂SO_{4 (aq)} + 2NaOH _(aq) → 2H₂O _(l) + Na₂SO_{4 (aq)}

   According to the balanced equation, 1 mole of H₂SO₄ is equivalent to 2 moles of NaOH.

2. Convert the number of moles of H₂SO₄ used to moles of NaOH used.

   

3. Calculate the molarity of the unknown NaOH solution.