An Acid-Base Titration

An Acid-Base Titration

Objective:

The purpose of this experiment is to determine the concentration of a solution, sodium hydroxide by titration against a standard solution of potassium hydrogen phthalate.

Theory:

Titration is the process of carefully measuring the volume of a sodium hydroxide required to react with a potassium hydrogen phthalate. Potassium hydrogen phthalate is a primary standard because it is solid and air stable, making it easier to weigh accurately. Potassium hydrogen phthalate has the formula C8H4O4K, but since it behaves as a monobasic acid in producing one mole of hydrogen ions per mole of compound, the compound can be simplified as HA Potassium hydrogen phthalate is dissolved in water in a flask, and phenolphthalein indicator is added. The sodium hydroxide solution is added from a burette into the flask containing the potassium hydrogen phthalate. Potassium hydrogen phthalate and sodium hydroxide would react with one another according to the equation:

HA (aq) + NaOH (aq) ( Na+ A¯ (aq) + H2O (l)

Phenolphthalein is used in order to show the equivalence point. It is colorless in acid and pink in alkaline solution. The point at which the addition of one drop (or even less) of indicator changes the solution from colorless to just faintly pink is called the end-point, and this indicates that the reaction is just completed.

Results:

|Pipette solution |Potassium hydrogen phthalate | 0.0984 mol dm ³ | 250cm‾ ³ |

|Burette solution |Sodium hydroxide | 0.0888 mol dm‾ ³ | |

|Indicator |Phenolphthalein | |

| | |Trial |1 |2 |3 |...