Passage VI
A typical acid-base indicator is a compound that will be one color over a certain lower pH range but will be a different color over a certain higher pH range. In the small range between these pH ranges—the transition range—the indicator's color will be an intermediate of its other 2 colors.
Students studied 5 acid-base indicators using colorless aqueous solutions of different pH and a well plate (a plate containing a matrix of round depressions—wells—that can hold small volumes of liquid).
Experiment 1
The students added a pH=0 solution to 5 wells in the first column of the well plate, then added a pH=1 solution to the 5 wells in the next column, and so on, up to pH=7. Next, they added a drop of a given indicator (in solution) to each of the wells in a row, and then repeated this process, adding a different indicator to each row. The color of the resulting solution in each well was then recorded in Table 1 (B=blue, G= green, O=orange, P=purple, R=red, Y=yellow).
Experiment 2
Experiment 1 was repeated with solutions that had a pH of 8 or greater (see Table 2).
Experiment 3
Students were given 4 solutions (Solutions I-IV) of unknown pH. The well plate was used to test samples of each solution with 4 of the 5 indicators (see Table 3).
31. Based on the results of Experiments 1 and 2, which of the following is a possible transition range for curcumin?
Your Answer is
Correct Answer is C
Explanation
From table 1, it can be seen that when the pH range is from 0-1, the color of D51Curcumin is yellow;
Look at table 2, when the pH is 8, the color of Curcumin Become orange, when the pH is 9, the color changes to red, so the transition range should be between pH 7-9, option C is in line