Identification of common gases common mistakes

Common mistakes

• Misunderstanding the Milky Appearance

  Students often state that the milky appearance in limewater is due to the color change rather than the formation of a solid precipitate.

  Fix itStudents should remember that the milky appearance is specifically caused by the formation of calcium carbonate precipitate when carbon dioxide reacts with limewater.

• Misinterpreting Limewater Test

  Students often confuse the milky appearance of limewater with the presence of other gases, such as chlorine.

  Fix itRemember that limewater turning milky specifically indicates carbon dioxide is present, and ensure to distinguish this test from others.

• Confusing Gas Tests

  Students often confuse the test for carbon dioxide with the tests for hydrogen and oxygen.

  Fix itRemember that carbon dioxide is tested using limewater, while hydrogen is tested with a lighted splint and oxygen with a glowing splint.

• Confusing Chlorine Test with Other Tests

  Students often confuse the chlorine test with the tests for hydrogen, oxygen, and carbon dioxide.

  Fix itTo fix this, students should focus on the specific method used for the chlorine test, which involves using damp litmus paper that bleaches when chlorine is present.

• Chlorine Test Confusion

  Students often confuse the chlorine test with the hydrogen test, thinking that both involve a color change.

  Fix itRemember that chlorine bleaches damp litmus paper, while hydrogen does not cause any color change.

• Confusing Chlorine Test with Other Tests

  Students often confuse the test for chlorine with tests for hydrogen, oxygen, and carbon dioxide, leading to incorrect interpretations of results.

  Fix itTo fix this, students should focus on the specific observation of damp litmus paper bleaching, which is unique to chlorine, and practice distinguishing it from the other gas tests.

• Damp Litmus Paper Requirement

  Students often forget that the litmus paper must be damp for the chlorine test, thinking that dry paper is sufficient.

  Fix itRemember that chlorine gas needs moisture to react with the litmus paper, which allows it to bleach the paper effectively.

• Confusing Gas Tests

  Students often confuse the chlorine test with the hydrogen test, thinking both involve a color change.

  Fix itRemember that the chlorine test uses damp litmus paper that bleaches, while the hydrogen test produces a squeaky pop with a lighted splint.