A student is given a clear, colourless aqueous solution of an unknown organic compound. Which of the following tests and subsequent observations would confirm that the solution is acidic?
Adding a few drops of phenolphthalein indicator, resulting in the solution turning a deep pink colour.
Dipping a strip of red litmus paper into the solution, which subsequently turns blue.
Adding solid NaHCO3\text{NaHCO}_3NaHCO3, resulting in effervescence of a gas that turns limewater cloudy.
Adding aqueous BaCl2\text{BaCl}_2BaCl2, resulting in the formation of a dense white precipitate.
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.