When magnesium ribbon is added to dilute hydrochloric acid, hydrogen gas is produced.
Which observation shows that a gas has been produced?
A solid precipitate forms at the bottom of the tube
Effervescence is observed in the test tube
The solution turns from blue to colourless
The magnesium ribbon melts into a shiny sphere
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.