QUALITATIVE CHEMICAL ANALYSIS

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QUALITATIVE CHEMICAL ANALYSIS
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Qualitative vs. Quantitative

• A qualitative characteristic is a description of
  something that does not involve numbers or units
  of measurement.
• If number and units are used then we are using a
  quantitative method of describing the object.
• How could you describe a fire truck both
  qualitatively and quantitatively?
• How could you describe a substance both
  qualitatively and quantitatively?

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CHEMISTRY CSI

• You can use the solubility rules to determine the
  presence of certain ions in a solution by
  conducting double displacement reactions.
• All you need to do is mix your water sample that
  contains the suspected ion with a solution that
  contains the ions that form a precipitate with
  your suspect ion.

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EXAMPLE 1

• Lets say you suspect your water sample has
  acetate in it. What could you do?
• If you combine your water sample with a solution
  that contains silver ions (Ag) then you can
  detect the presence of acetate because silver
  acetate will form which is insoluble meaning it
  will form a precipitate.
• Ag(aq) C2H3O2-(aq) ? AgC2H3O2 (s)

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THE BIG PROBLEM

• The major issue that has to be dealt with is that
  most solutions or samples contain more than one
  type of ion so chemists must design test
  procedures to identify and remove any suspected
  ions one at a time
• You need to find a solution that will react (form
  a precipitate) with only one of the ions at a
  time.

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EXAMPLE 2

• Lets say we suspect a solution has both iron
  (Fe2) and strontium (Sr2) ions in it.
• Solubility rules say that hydroxide ions (OH-)
  will react with the iron ions (Fe2) and form a
  precipitate but will not have the same reaction
  with strontium ions.
• So we can simply add a solution of sodium
  hydroxide (NaOH). This will dissociate and the
  hydroxide ions (OH-) will form a precipitate with
  the iron ions (Fe2) in the solution.
• Fe2(aq) OH-(aq) ? Fe(OH)2(s)

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EXAMPLE 2Part 2

• To remove the iron out of the solution we will
  centrifuge the solution with the precipitate. The
  rapid spinning will force the more dense
  precipitate to the bottom of the test tube and
  the liquid with the strontium ions in it will
  remain on top.
• The solution containing the strontium ions is
  called the supernate. We keep this for further
  testing.

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EXAMPLE 2Part 3

• Now we have the supernate with the strontium ions
  in ithow do we test for the strontium ions?
• Sulfates (SO42-) will form precipitates with
  strontiumso we need to add an aqueous solution
  that contains sulfate ionslike sodium sulfate
  (Na2SO4).
• The precipitate that forms will contain the
  precipitate called strontium sulfate.
• Sr2(aq) SO42-(aq) ? SrSO4 (s)

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Thats All I Got