During a synthesis experiment, a chemist prepares a sample of sulfur dioxide gas, SO2SO_2SO2, which is significantly denser than air. The gas is collected in an upright, open-topped gas cylinder by downward delivery.
To determine when the cylinder is full of the acidic gas, a strip of damp blue litmus paper is positioned at the top rim of the cylinder.
Explain the chemistry and physical reasoning behind using litmus paper that is damp and placing it specifically at the top rim of the cylinder.
276 exam-style questions on Edexcel GCSE Chemistry 4.1 Acids, covering 4.1.1 Acids, alkalis and the pH scale, 4.1.2 Hydrogen ion concentration and pH, 4.1.3 Dilute and concentrated, weak and strong acids, 4.1.4 Bases, alkalis and the reactions of acids, 4.1.5 Chemical tests for hydrogen and carbon dioxide, 4.1.6 Neutralisation as a reaction of acids with bases, 4.1.7 Preparing soluble salts, and 4.1.8 Solubility rules and preparing insoluble salts. Each one has a worked solution and a mark scheme showing where the marks go.