The table below shows the color of three indicators at different pH values:

Question

Indicator | pH=0 | pH=2 | pH=4 | pH=6 | pH=8 | pH=10 | pH=12 | pH=14
Litmus paper | Red | Red | Red | Red | Blue | Blue | Blue | Blue
Phenolphthalein | No change | No change | No change | No change | No change | Pink | Pink | Pink
Thymol blue | Red | Red | Yellow | Yellow | Yellow | Blue | Blue | Blue

An unknown liquid is tested with three indicators:
• The unknown liquid turns litmus paper blue.
• The unknown liquid is not affected by phenolphthalein indicator.
• The unknown liquid turns yellow when tested with thymol blue indicator.

What is the pH of the unknown solution?
A. 2
B. 6
C. 8
D. 12

Answer 1

To determine the pH of the unknown solution based on the indicators' responses, let's analyze the provided information step by step:

1. Litmus Paper: The unknown liquid turns litmus paper blue. According to the table, litmus paper turns blue at a pH of 8 or higher. Therefore, we can conclude that the pH of the unknown solution is at least 8.

2. Phenolphthalein: The unknown liquid does not affect the phenolphthalein indicator. Phenolphthalein remains colorless at pH values from 0 to 8 and turns pink at pH 10 and above. Since the unknown liquid does not change color, its pH must be 8 or lower.

3. Thymol Blue: The unknown liquid turns yellow when tested with thymol blue. According to the table, thymol blue turns yellow at pH 6 to 8. Since we have already established from litmus paper that it is at least 8 and from phenolphthalein that it is 8 or lower, we can further confirm that the pH must be 8, because it cannot be greater than this based on the reaction with phenolphthalein.

Bringing this all together, the only pH that satisfies all conditions is pH 8.

Thus, the answer is: C. 8