Qualitative analysis – the identification of the specific substances present Quantitative analysis – the measurement of the quantity of a substance present

Qualitative Analysis Many substances can be identified by their unique physical or chemical properties: 1.Observation of colour of solution 1.Reactions with other substances to produce a new colour and/or precipitate 1.For cations that are usually colourless in solution and highly soluble, a flame test may be used (only works when a single cation is present)

1. Qualitative Analysis – Colour of Solution

2. Qualitative Analysis – Reactions in Solution This is a type of test where we set up a double displacement reaction using one unknown solution and one known solution In this test, we would predict that if a precipitate forms then a certain ion must have been present in the unknown solution

Indicate the test being performed Positive TestObservationsAnalysisConclusionNegative TestObservationsAnalysisConclusion

To Complete A Sequential Analysis 1.Locate the possible cations on the solubility table. 1.Determine which anions would precipitate the possible cations. 1.Plan a sequence of precipitation reactions that would use anions to precipitate a single cation at a time. 1.Use filtration between the steps to remove cation precipitates that might interfere with subsequent additions of anions. 1.Draw a flow chart to assist testing & communication.

Example 1 A solution known to contain Pb 2+ Positive test is a white precipitate Solution contained Lead(II) ions, precipitated as PbCl2 Negative test is no precipitate No Lead (II) ions present Add NaCl

Example 2 A solution known to contain Sr 2+ Positive test is a white precipitate Solution contained Sr 2+ ions, precipitated as SrSO4 Negative test is no precipitate No Sr 2+ ions present Add Na2SO4

Example 3 A solution known to contain Cu 2+ Positive test is a white precipitate Solution contained Copper (II) ions, precipitated as Cu(OH)2 Negative test is no precipitate No Copper (II) ions present Add NaOH

You try! Design a sequential analysis for each of the ions below, to determine if it is present in the solution. a.Ag + b.Ca 2+ c.Mg 2+

Example with Two Ions A solution is thought to contain lead (II) and magnesium. Design a sequential qualitative analysis to determine whether the solution contains either or both of these ions

Solution known to contain Pb 2+ (aq) or Mg 2+ (aq) If Solution contains Pb 2+ ions, a ppt will form of PbCl2 Solution contained Pb 2+ ions, precipitated as PbCl2 If Solution does not contain Pb 2+ ions then no ppt will form No Lead (II) ions present Add NaCl – the Na + is always soluble, the Cl - will ppt with Pb 2+, the Cl - is soluble with Mg 2+

If a positive test occurred, filter off the ppt and run a second test for the second cation

Add Na2CO3 – again, Na + is always soluble, but the CO 3 2- will ppt with Mg 2+ If a white ppt forms, the Mg 2+ ions present in form if MgCO3 If no ppt forms then no Mg 2+ was present

Another Example with Two Ions A solution is thought to contain calcium and mercury. Design a sequential qualitative analysis to determine whether the solution contains either or both of these ions

Solution known to contain Ca 2+ (aq) or Hg 2+ (aq) If Solution contains Hg 2+ ions, a ppt will form of HgCl2 Solution contained Hg 2+ ions, precipitated as HgCl2 If Solution does not contain Hg 2+ ions then no ppt will form No Hg 2+ ions present Add NaCl – the Na + is always soluble, the Cl - will ppt with Hg 2+, the Cl - is soluble with Ca 2+

If a positive test occurred, filter off the ppt and run a second test for the second cation

Add Na 2 SO4 – again, Na+ is always soluble, but the SO 4 2- will ppt with Ca2+ If a white ppt forms, the Ca 2+ ions present If no ppt forms then no Ca 2+ was present

You Try!! Design a sequential analysis for each of the pairs of ions below, to determine if one or both are present in the solution. a.Ba 2+ and Pb 2+ b.Ag + and Zn 2+ c.Sr 2+ and Mn 2+ d.Cu + and Fe 3+

Solution known to contain Ag +1 aq or Cu 2+aq or Ba2+ ion Chose an anion that will produce a ppt for one of the cations Add NaCl – the Na + is always soluble, but the Cl - will ppt with Ag 1+ If Solution contains Ag 1+ ions, a ppt will form of AgCl If Solution does not contain Ag 1+ ions then no ppt will form Example containing three ions!

If a positive test occurred, filter off the ppt and run a second test for the second cation

Add NaOH – This causes basic conditions and OH - ion will ppt with Cu 2+ (Ba 2+ is soluble with OH -) If a ppt forms, the Cu 2+ ions present in the form of Cu(OH)2 If no ppt forms then no Cu 2+ was present

If a positive test occurred, filter off the ppt and run a third test for the third cation

Add Na2SO4 –Na + is always soluble and Ba 2+ ion will ppt with SO 4 2- ion If a ppt forms, the Ba 2+ ion present If no ppt forms then no Ba 2+ was present

3. Qualitative Analysis – Flame Test The majority of solids are white powders and difficult to distinguish between just by looking. Flame tests can give a good indication of what metal ion it contains.

You should perform the colour of solution test and the PPT tests to narrow down which ions you think are present. You should also determine the colours that each ion would produce in a flame test before performing the flame test The flame test is not used to confirm or eliminate the presence of a particular ion.

4. Qualitative Analysis – Gas Test Most gases are clear, colourless and odourless. So it's not easy to distinguish between them with a simple chemical test.

Test for Hydrogen Hydrogen is less dense than air and explosive when mixed with Oxygen. A test-tube filled with hydrogen can be safely held up-turned since no Hydrogen can escape by sinking into denser air.

Oxygen Test Oxygen has a similar density to air, so needs to be contained in a "right-side up" container So, if we light a splint and blow out the flame so that the end is still glowing (the reason the flame does not reappear is that 79% of the air around it is not Oxygen) Placing the glowing splint in pure Oxygen means that every gas molecule that collides with the glowing ember is Oxygen. This increases the rate of reaction, providing enough heat to re-light the flame.

Carbon Dioxide Test Carbon Dioxide puts out fires. But so do most other gases. So the test for Carbon Dioxide must be something that only Carbon Dioxide does. Only Carbon Dioxide turns Lime-water milky white The white colour is a precipitate of Calcium Carbonate ( like chalk).