Passage II

The rate of a chemical reaction can be measured as the change in the concentration of its products over a period of time. The following experiments were performed to investigate factors that influence the rate at which potassium permanganate (KMnO₄) reacts with oxalic acid（H₂C₂O₄) to form Mn²⁺and other products.

Experiment 1

A 4.0 mL sample of 0.1 M (moles/liter) aqueous KMnO₄, which was purple in color, was measured with a clean graduated cylinder and poured into a test tube. A 4.0 mL sample of 1.0 M aqueous H₂C₂O₄ was then measured with a clean graduated cylinder and poured into a second test tube. The 2 test tubes were placed in a 25℃ water bath. After 5 minutes the H₂C₂O₄ solution was mixed with the KMnO₄ solution and placed back in the water bath. The time until the purple color disappeared was recorded. This procedure was repeated at 3 other temperatures. The results are shown in Table 1.

Experiment 2

The procedure from Experiment 1 was repeated in every way except that 0.1 mg of manganous sulfate（MnSO₄), a catalyst, was added to each test tube containing KMnO₄ before the H₂C₂O₄ was added. Catalysts are substances that increase the rate of reactions without being used up. The results are shown in Table 2.

Experiment 3

The procedure from Experiment 1 was repeated at a constant temperature of 25°C and various concentrations of H₂C₂O₄. The results are shown in Table 3.