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).

34. Based on the results of Experiments 1-3, which of Solutions I-IV has the lowest pH ?

Answer and Explanation

Your Answer is

Correct Answer is J

Explanation

Looking at table 3, it can be found that the color of Solution IV is orange after adding Metanil yellow, while the color of the other three solutions is yellow;

Looking at table 1, it is found that adding Metanil yellow is an indicator, When the solution shows orange, the pH will be lower than that of yellow, so the pH of Solution IV is the lowest