What is the pH range and color of a weak alkali using a universal indicator?

What is the pH range and color of a weak alkali using a universal indicator?

• A. 6-8, green
• B. 8-10, blue
• C. 10-12, yellow
• D. 11-13, purple

Answer: (B)

A weak alkali typically has a pH range of about 8 to 10. In this range, a universal indicator would show a blue color. This is because universal indicators respond to the concentration of hydrogen ions (H⁺) in a solution, which decreases in a weak alkali, leading to a higher pH. When a substance is a weak alkali, it partially dissociates in water to produce hydroxide ions (OH⁻) but not to the extent that strong alkalis do. A solution with a pH below 7 is acidic, a pH of 7 is neutral, and any pH above 7 indicates basicity. Therefore, those solutions that range from 8 to 10 indicate weak alkalinity, which is precisely what would correspond to the blue color observed in the universal indicator. Other options reflect either incorrect pH ranges for weak alkalis or different colors associated with those ranges. For instance, a pH of 6-8 is not sufficiently basic to describe a weak alkali, while a range of 10-12 suggests a stronger alkali, paired with a different color (yellow). The highest pH range, 11-13, indicates a strong alkali

A weak alkali typically has a pH range of about 8 to 10. In this range, a universal indicator would show a blue color. This is because universal indicators respond to the concentration of hydrogen ions (H⁺) in a solution, which decreases in a weak alkali, leading to a higher pH.

When a substance is a weak alkali, it partially dissociates in water to produce hydroxide ions (OH⁻) but not to the extent that strong alkalis do. A solution with a pH below 7 is acidic, a pH of 7 is neutral, and any pH above 7 indicates basicity. Therefore, those solutions that range from 8 to 10 indicate weak alkalinity, which is precisely what would correspond to the blue color observed in the universal indicator.

Other options reflect either incorrect pH ranges for weak alkalis or different colors associated with those ranges. For instance, a pH of 6-8 is not sufficiently basic to describe a weak alkali, while a range of 10-12 suggests a stronger alkali, paired with a different color (yellow). The highest pH range, 11-13, indicates a strong alkali