The rate of a chemical reaction is obtained by dividing the amount of a chemical consumed in a reaction by the time in which the chemical is consumed. The rate at which a chemical reaction occurs is dependent on many variables, two of which are the concentration of a chemical in solution and the temperature at which the reaction occurs. In order to determine the effect of concentration and temperature on reaction rates, a chemist studied the following reaction sequence.HCHO + Na2SO3 + H2O → NaO3SOCH3 + NaOHReaction 1NaOH+ NaHSO3 → Na2SO3 + H2OReaction 2While Reaction 1 occurs slowly, Reaction 2 happens instantaneously. Both of the reactions occur in the same solution and base (NaOH) is built up in solution until all the NaHSO3 is used. Phenolphthalein, which is also in the solution, will cause the solution to turn pink when a measurable amount of base is present.Experiment 1:A standard solution of formaldehyde (HCHO) in water was prepared. This solution contained 0.3 mole of HCHO per liter of solution (0.3 M HCHO) and a small amount of phenolphthalein. This solution was diluted further with varying amounts of water and mixed with 10.0 mL of a 0.01 M solution of both Na2SO3 and NaHSO3 in water. The time required for pink color to appear is shown in Table 1.In order to display the relationship between concentration and the rate of the reaction more effectively in Experiment 1, the chemist could:

Correct answer: A. Make a bar graph of the concentration of formaldehyde in each trial

• A. Make a bar graph of the concentration of formaldehyde in each trial
• B. Plot the HCHO concentration against the time required for the color change
• C. Plot the change in tHCHO and NaHSO3 in each trial against that in HCHO concentrations
• D. Produce a dual cataloging: the differences between the times for the color change in successive trials

Last updated 3 September 2026