Reactions of ions in aqueous solution (A-level only) common mistakes

Common mistakes

• Incorrectly balancing equations

  Failing to balance the number of atoms of each element on both sides of the equation.

  Fix itAlways check that the number of atoms for each element is the same on both sides of the equation.

• Confusing precipitate colors

  Students often confuse the color of iron(III) hydroxide with that of copper(II) hydroxide.

  Fix itRemember that iron(III) hydroxide is reddish-brown, while copper(II) hydroxide is blue.

• Confusing sulfate and sulfite tests

  Using barium chloride to test for sulfite ions instead of sulfate ions.

  Fix itBarium chloride is used for sulfate ions; sulfite ions require a different test, such as adding hydrochloric acid to produce sulfur dioxide.

• Misidentifying precipitate colors

  Confusing the colors of precipitates formed by different ions.

  Fix itAlways refer to known data for the specific colors of precipitates for accurate identification.

• Misidentifying ions

  Confusing the tests for sulfate and carbonate ions.

  Fix itRemember that sulfate ions produce a white precipitate with barium chloride, while carbonate ions produce carbon dioxide with dilute acid.