Passage VI

When sucrose is dissolved in an aqueous solution, it can hydrolyze (react with H₂O to break down) to form glu­cose and fructose. The compound imidazole catalyzes the hydrolysis:

To study this reaction, chemists prepared several buffer solutions. (A buffer solution is a solution that main­tains a stable pH.) Each buffer solution had a different pH.

Experiment 1

In each trial, Steps 1-4 were followed:

1. A certain mass of imidazole (or no imidazole) was dis­solved in a certain volume of a buffer solution having a pH of 5.24.

2. A test tube containing 8.0 mL of this imidazole solution (or of the buffer solution only) and a test tube containing 2.0 mL of a 500.0 g/L sucrose solution were each par­tially submerged in a water bath maintained at 85°C.

3. After 30 min, the reaction solution was formed by adding the 8.0 mL of imidazole solution (or of the buffer solution only) to the test tube containing the 2.0 mL of sucrose solution.

4. The concentration of sucrose in the reaction solution was monitored over the next 35 min while the solution was kept at 85°C.

In no two trials was the same mass of imidazole added to the buffer solution.

The measured values of sucrose concentration were then used to calculate values of the total mass of sucrose that was hydrolyzed. Figure 1 shows how the total mass of sucrose that was hydrolyzed varied over time for reaction solutions having 6 different imidazole concentrations.

Experiment 2

Experiment 1 was repeated except that, from trial to trial, the pH of the buffer solution was varied and the mass of imidazole added to the buffer solution remained constant (see Figure 2).