Chemistry Unit 3: Identifying and Analysing Substances

  • Gas tests
  • Tests for Positive Ions: Precipitate and Flame tests
  • Tests for Negative Ions
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Ways of Collecting Gases

  • A gas syringe can be used to collect nearly any gas

(http://www.thesciencefair.com/Merchant2/graphics/00000001/GasSyringePlstc322_M.jpg)

  • A side-arm flask can be used too. It can be connected to a delivery tube to bubble gas into an upside-down measuring cylinder or a gas jar filled with water. This method only works for insoluble gases. It can't be used for collecting hydrogen, chlorine and ammonia as they dissolve in water. 

(http://www.practicalchemistry.org/data/images/originals/estimation-of-the-concentration-of-household-bleach-240.jpg)

Upward and Downward delivery

  • Upward delivery is used if the gas you want to collect is lighter than air e.g. hydrogen.

(http://www.bbc.co.uk/schools/gcsebitesize/science/images/43_1_upward_downward_delivery.gif)

  • Downward delivery is used if the gas you want to collect is heavier than air e.g. carbon dioxide, chlorine.

(http://www.bbc.co.uk/schools/gcsebitesize/science/images/43_2_upward_downward_delivery.gif)

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