A technician monitors the pH of water during a process that removes a dark blue dye. Every sample is still dark blue. The pH is expected to change by about 0.2 during the process, and 50 cm3 of each sample is available.
| Method | Minimum sample needed with the available equipment | How the pH is recorded |
|---|---|---|
| Universal indicator paper | one drop | whole-number pH from a colour chart |
| pH probe | 20 cm3 | pH to two decimal places |
Use the information in the table to evaluate which method the technician should use to monitor the pH. Include how the chosen method should be used to obtain reliable results over time.
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.