Tests For Ions

• What are cations?

  Positively charged ions
• How do cations form?

  When atoms lose electrons
• What results from the loss of electrons in cations?

  More protons than electrons
• Which group of metals typically forms cations?

  Group 2 metals
• What do Group 2 metals produce in flame tests?

  Distinct flame colours
• What is the first step in conducting a flame test?

  Clean a wire loop with hydrochloric acid
• What material is the wire loop usually made from?

  Platinum or nichrome
• How do you identify the metal ion in a flame test?

  Observe the colour produced
• What flame colour does calcium (Ca$^{2+}$) produce?


  Brick-red flame
• What flame colour does strontium (Sr$^{2+}$) produce?


  Scarlet-red flame
• What flame colour does barium (Ba$^{2+}$) produce?


  Pale-green flame
• How can dilute sodium hydroxide (NaOH) be used in identifying Group 2 metal ions?

  It forms precipitates with most Group 2 hydroxides
• What is the procedure for identifying Group 2 ions using NaOH?

  1. Add dilute NaOH to the solution.
  2. Look for any initial precipitate.
  3. Add NaOH dropwise until in excess.
  4. Observe any changes in the precipitate.
• What is released when ammonium ions (NH$_{4}^{+}$) are heated with sodium hydroxide?


  Ammonia (NH$_{3}$)
• What happens to damp red litmus paper when ammonia is released?

  It turns blue
• What is the first step in testing for ammonium ions?

  Add sodium hydroxide to the solution
• What indicates the presence of sulphate ions in a solution?

  Formation of a white precipitate
• What is the ionic equation for the reaction of barium ions with sulphate ions?

  Ba$^{2+}$ + SO$_{4}^{2-}$ → BaSO$_{4}$ (s)
• How can hydroxide ions (OH$^{-}$) be detected?


  Using pH indicators or litmus paper
• What colour does red litmus paper turn in the presence of hydroxide ions?

  Blue
• What happens when ammonium chloride is added to a solution containing hydroxide ions?

  Ammonia gas is released
• What is the result of adding dilute nitric acid before silver nitrate in halide ion testing?

  Removes interfering ions
• What precipitate forms when silver nitrate is added to chloride ions?

  White silver chloride
• What precipitate forms when silver nitrate is added to bromide ions?

  Cream silver bromide
• What precipitate forms when silver nitrate is added to iodide ions?

  Yellow silver iodide
• How does the solubility of silver halides change with ammonia?

  AgCl is soluble, AgBr is slightly soluble, AgI is insoluble
• What indicates the presence of carbonate ions (CO$_{3}^{2-}$) in a solution?


  Effervescence or bubbling
• What happens when carbonate ions react with dilute acid?

  They release carbon dioxide gas
• What happens to limewater when carbon dioxide is bubbled through it?

  It turns cloudy
• What is the reaction equation for carbon dioxide with limewater?

  CO$_{2}$ + Ca(OH)$_{2}$ → CaCO$_{3}$ (s) + H$_{2}$O (l)
• What are the steps to test for carbonate ions?

  1. Add dilute acid to the solution.
  2. Look for effervescence or bubbling.
  3. Bubble the gas through limewater.
  4. Observe if limewater turns cloudy.