Cambridge Secondary (7-9). Stage 7. Science. Learner's Book - Unit 8: Changes to materials - Question 30

In Activity 8.2.1, a washing-soda crystal is placed at the bottom of a clamped test tube; water and universal indicator are added, then acid is carefully added at the top. The tube is left still for a few days.

What is the pH at the top part of the test tube?