Buffer Experiment

ABSTRACT

This experiment is about buffer and pH changes. Buffer is an aqueous solution consisting of a mixture of either a weak acid and its conjugate base or weak base with its conjugated acid. It means that it has the property that the pH of the solution changes very little when a small amount of acid or base is added to it. Buffer solutions are used as a means of keeping pH at a nearly constant value in a wide variety of chemical applications. The experiment is carried out to helps us understand the nature of a buffer solution and how to prepare a buffer from acetic acid and sodium acetate. Moreover it is also to test the ability of buffered and un-buffered solutions to resist pH changes when strong acids and bases are added.

Based on

Whereas toward strong base is beaker 10 which contain 50mL of 0.1M acetic acid and 10g of sodium acetate.

Two important characteristics of a buffer solution are its pH and its buffer capacity. The buffer capacity is the amount of acid or base that can be absorbed by the buffer solution without a significant change in pH. The larger the buffer capacity, the greater the amount of acid and base must be added in order to produce a specific change in pH. The buffer capacity depends on the concentration of the weak acid and its conjugate base present. Maximum buffer capacity exists when the concentrations of a weak acid and its conjugate acid are kept large and approximately equal to each other.

Rinse off the pH probe using distilled water to make sure it is neutral before measure the pH value as it will influence the pH value. During the experiment, the pH meter must rinse out using distilled water and the solution inside the pH meter to make sure it is neutral before measure the pH value. So that, the pH will more accurate. Since we know that the pH change for buffer solution toward acid is a smallest compare toward base , hence we can conclude that the greatest buffer capacity is toward HCl

The sodium hydroxide must be added to the beaker until there are slightly changes of pH value. There are no best results of buffer solution for these beakers. There have a huge amount of pH value before added the

sodium hydroxide and after added sodium hydroxide for these solutions. The most slightly changes of pH value is 2.71 for the1 gram of sodium acetate with 50 ml of CH3COOH.

Distilled water is used for rinse off the pH probe because it has no mixture of substances, it just has H2O. Compare to the water bath, it has many substances such as chlorine and mineral salt. If we used water bath to rinse off the pH probe it will affected to the chemical. So, distilled water is more effective to rinse off the pH probe. The NH3/NH4NO3 because NH3 is the weak base and also conjugate acid. While NH4NO3 is the weak acid.

The pH of the buffer system 0.15M NH3 / 0.35 M NH4C is

Kb for NH3 = 1.8 x 10-5 mol dm-3 Using the Henderson-Hasselbalch