International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

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What is the universal indicator color of a weak acid?

Red
Yellow
Green
Blue

The correct answer is: Yellow

A weak acid typically has a pH that ranges from just below 7 to around 6, depending on its concentration. When using a universal indicator, which is a pH indicator that displays a variety of colors across different pH levels, a weak acid would show a yellow color. This yellow color is indicative of a pH level that is slightly acidic, confirming the presence of a weak acid solution. In contrast, a strong acid would produce colors in the red range due to a lower pH, while a neutral substance would appear green, reflecting a pH close to 7. A blue color would indicate a more alkaline (basic) pH, which would not be associated with acid solutions at all. Thus, the universal indicator showing a yellow color in the context of a weak acid is the correct identification of its pH level.