A technician records the pH of samples collected from the same pond on two days. The readings are expected to differ by only 0.2 pH units.
Why would the technician select a pH probe rather than universal indicator paper?
The paper changes colour only in acidic samples, while the probe can measure any pH value.
The paper must be rinsed between samples, while the probe does not need any rinsing.
The probe uses a larger volume of each sample, which makes every pH reading more precise.
The probe gives the pH to one or two decimal places, while the paper gives a whole number.
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.