Summary:

Titration is an experimental technique that allows us to know the concentration of an unknown acid or base.
The method relies on the principle of neutralization of an acid with a base.

The volumetric method illustrated here is to determine the volume Vb of a known base with concentration Cb, that is necessary to neutralize a certain volume Va of an unknown acid of concentration Ca. In this animation, the base is NaOH (sodium hydroxide) and acid is HCl (hydrochloric acid). During the neutralization of the acid by the base, we get the following equation:
VaCa = VbCb
From this equality, we can deduce the concentration of the acid:
Ca = VbCb / Va
Click on the stopcock or the "add 5mL of NaOH" button.

Learning Goals

• To establish the link between pH and H + and OH-.
• To understand the principle of the neutralization of an acid with a base.
• To describe the protocol of a titration experiment.

Learn More

The pH is an important characteristic of aqueous solutions.  It indicates the acidity or basicity of the solution.

The pH is a measure of the presence of the hydrogen ion, H+. This ion is very involved in many chemical reactions. It is therefore an important parameter in chemistry, biology, medicine and ecology. The pH test is used to characterize the functioning of an organ (blood test, urine test) or quality of an environment (lake water, agricultural soil).

For many molecules that react with the H+ ion there is some color change visible to the eye. It is this property which is exploited by pH indicator paper, sold in rolls or strips.

The pH value is directly related to the measurement of the H+ ion concentration of a solution. This measure is logarithmic. Thus, a solution whose pH is 6 contains ten times more of H+ ions that a solution with a pH 7. It would have a hundred times more if the pH was 5.

H+ and OH- react easily with other molecules. They have a role in the combining or separation of certain molecules. The metabolism of living organisms is very much affected by changes in pH as it can cause a serious deterioration in the functioning of certain proteins or enzymes: 

• If human blood is too different from its nominal value of 7.4, dysfunction of certain cells can cause death.
• Rain water, the pH is slightly acidic (pH 6), can become toxic if the acidity is too high (pH <5.5), mainly due to air pollution. The effects are quickly visible on affected plants.
• A solution with a pH very high or very low is corrosive. It destroys long chains of molecules. This is the case in our stomach where gastric juices digest very acidic foods. Such products must be handled carefully because the damage is irreversible.