A technician tests four colourless waste-water samples from a chemical plant using universal indicator.
| Sample | Colour with universal indicator |
|---|---|
| A | red |
| B | purple |
| C | green |
| D | blue |
Which statement about the samples is correct?
Sample C has a pH above 7.
Sample D has a higher pH than sample B.
Sample B has a pH below 7.
Sample A has the lowest pH.
112 exam-style questions on OCR GCSE Chemistry 3.3 Types of chemical reactions, covering 3.3.1 Oxidation and reduction in terms of oxygen, 3.3.2 Acids, alkalis and neutralisation, 3.3.3 The pH scale and measuring pH, 3.3.4 Oxidation and reduction in terms of electrons, 3.3.5 Dilute and concentrated, weak and strong acids, and 3.3.6 Hydrogen ion concentration and pH. Each one has a worked solution and a mark scheme showing where the marks go.