Buffers Lab

The purpose of this experiment was to create two 40 mL buffers and evaluate its buffer capacity at pH 4. To do this, buffer #1 consisted of the mixture of 0.5003 M acetic acid and .50 M sodium acetate, while buffer #2 consisted of the mixture .5003 M acetic acid and .4289 M NaOH. Within each mixture, there is a ratio of conjugate acid to conjugate base. By using the Henderson Hasselbalch equation, the volume for the base and acid to buffer the pH of solution at 4.0 were calculated. Two titration were performed for each buffer: HCl and NaOH. A pH meter was used to record the pH change, and the volume of the buret was recorded every .1 change in pH. This potentiometric titration method was stop once the solution change by 2 pH units. The

Whereas, the initial pH of Buffer #2 before titrated with NaOH was 3.851 and was 3.806 before titrated with HCl. This pH is close to the assigned pH of 4. However, the pH of the buffer was not exact because the concentration of the stock solutions may not be accurate. Although the calculations could have been correct, the mixture of the stock solutions would not give our exact desire pH. The pH of the buffer was closest to 4 during the 1st titration with NaOH. However, during the last 3 titrations, the initial pH of the buffers were much less than 4. The reason this occur may also been due to the presence of CO2 in the room that may have reacted with hydrogen ions in, forming carbonic acid. This would make the pH lower throughout the rest of the

The acid region is the curve on the left of the graph, whereas the base region is on the left. When HCl was added to both buffer, the pH of the buffer decrease. Ideally, the designed buffer can maintain the pH at 1 units: in this case between 3 to 5. Once the pH surpassed these change, the change in volume and pH will be drastic. As seen in the trend of both buffer, once the pH is lower than 3, the slope of dv/dpH increase drastically, showing the decreasing effects of the buffer. On the other hand, in the trend of both buffer on the right side of graph shows when NaOH is added, the change in pH is more drastic once past about pH 5. Although buffer 1 and buffer 2 shows a similar trend, the plot of buffer 1 is above the plot of buffer 2. The reason for this is that buffer 1 is made by an acid and base with an almost equal concentration. This makes buffer 1 a greater buffer compared to buffer 2. This is not true for Buffer 2 because the because NaOH was added to acetic acid to form acetate ions as conjugate base: The graph 1 shows the buffer capacity of buffer 1 is at pH 4.559 as it takes about 7.5 mL to change the pH. Whereas the buffer capacity of buffer 2 is at pH 4.756, which takes 5.9 mL to change the pH. These number shows buffer 1 has higher buffer capacity. The pH at 4.559 is significant as once the pH exceeded this value, the buffer will become ineffective.