Question

A sample of rain water turned universal indicator paper yellow. What would you expect its pH to be? Is it a strong or a weak acid?

Answer 1

A universal indicator shows a greenish-yellow colour at pH 6 and an orange-yellow colour at pH 5. This means that if the indicator turns yellow, the pH should be between these two values. Hence, it must have a pH value between 5 and 6. As the pH is closer to 7 (between 5 and 6), the acid is weak.