Читать книгу Food Chemistry - Dennis D. Miller - Страница 23

1 Calculate the amounts of citric acid monohydrate and 0.5 N KOH required to prepare 200 ml of 0.05 M citrate buffer, pH 3. Note: Even though citric acid is a triprotic acid, calculations for this pH range are made using pKa = 3.06.

2 Prepare 200 ml of the buffer.

3 Measure the pH of your buffer. Is it 3.0? If not, can you explain why?

4 Determine the buffer capacity of your buffer in the alkaline direction by titrating a 100 ml aliquot with 0.5 N KOH. Express buffer capacity as the number of moles of OH− required to increase the pH of 1 l of the buffer by 1 pH unit.

5 Repeat Step 4 using 0.001 N HCl in place of the citrate buffer, i.e. determine the buffer capacity of 0.001 N HCl.

6 Determine the buffer capacity of your buffer and 0.001 N HCl by calculation. Compare your experimental results with your calculated answers. Explain any discrepancies between experimental and calculated values.

7 Determine the buffer capacity of Sprite® in the same way you did for your citrate buffer (Step 4 above).