Experiment 1 Acid Base Titration

1695 Words7 Pages
Laboratory Manual, Physical Chemistry, Year 1 Experiment 1 ___________________________________________________________________________________ EXPERIMENT 1 ACID BASE TITRATION Objective : To determine pH curve for titration of strong acid-strong base and weak acid-strong base. 1 Theory The process of adding acid to a base (or vice versa) to produce a salt and water is called neutralization. In the neutralization of hydrochloric acid with sodium hydroxide, the reaction that occurs is: HCl + NaOH → H2O + NaCl When an acid and a base are present in stoichiometric amount, for example one mole of hydrochloric acid is added to one mole of sodium hydroxide as in the above neutralization process, this means that the equivalent point has been reached in the acid-base system. Suitable indicators (refer to table 1) can be used to monitor the end-point (the point at which an indicator changes colour) of the titration. Indicator Litmus Methyl Orange Colour in Acid RED RED End-point Colour PURPLE ORANGE Colour in Alkali BLUE YELLOW pKind 6.5 3.14.4 9.3 6.27.6 Titration to Use For Strong Acid - Strong Base Strong Acid - Strong Base or Strong acid Weak Base Weak acid and Strong Base Strong acid - Strong base Phenolphthalein Bromotymol Blue COLOURLESS YELLOW PALER PINK GREEN PINK BLUE Table 1: Common Indicators and Their Colours In the above example, pH of the hydrochloric acid will change with increasing amount of sodium hydroxide added. At the end-point the solution will become neutral with pH of 7. This is only true for strong acid-strong base titration. For strong acid-weak base, weak acid-strong base and weak acid-weak base titration, the salt that is formed may undergo hydrolysis and this may cause the pH not to be equal to 7 at the end-point. Graph of pH versus volume of base that is added to the acid of constant volume or otherwise is called the pH titration curve.

More about Experiment 1 Acid Base Titration

Open Document