Qualitative analysis
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Qualitative Analysis. Determines only the presence (or absence) of a substance Sometimes referred to as “Wet Chemistry” Involves the identification of ions present in solution. Qualitative Analysis.

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Qualitative Analysis

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Qualitative analysis

Qualitative Analysis

  • Determines only the presence (or absence) of a substance

  • Sometimes referred to as “Wet Chemistry”

  • Involves the identification of ions present in solution


Qualitative analysis1

Qualitative Analysis

  • General idea is to separate ions into large groups first, then separate and identify within each group

  • Classic scheme has five groups


Group 1

Group 1

  • Includes Ag+, Pb+2, and Hg2+2 ions

  • Separated out as insoluble chlorides by adding 6M HCl


Group 11

Group 1

  • The precipitate is then separated from the remaining liquid by first using a centrifuge.


Group 12

Group 1

  • Then, the liquid is extracted using a micropipette


Group 13

Group 1

  • The Ksp’s for each chloride are:

    • PbCl2 = 1.7 x 10-5

    • AgCl = 1.8 x 10-10

    • Hg2Cl2 = 1.2 x 10-18

  • Being the most soluble, the lead(II) chloride will dissolve fairly readily in hot water.

  • Thus, we will add DI water and heat in a hot water bath to dissolve this compound.


Group 14

Group 1

  • Once again, centrifuge and separate the liquid from the solid using the micropipette

  • The liquid will be tested for the lead ion by adding K2CrO4


Group 15

Group 1

  • The solid precipitate that remains will be treated with 6M NH3 with formation of a black solid confirming mercury(I) is present.


Group 16

Group 1

  • The liquid solution from the previous step is tested for silver ion by acidifying with HNO3. The formation of a white precipitate confirms this ion.


Litmus tests

Litmus Tests

  • Throughout the schemes, you may be required to add acid until the solution becomes acidic or base until it becomes alkaline.

  • “Blue” litmus  pink = acidic

  • “Red” litmus  blue = basic (alkaline)

  • Correct method – use stirring rod – dunk in solution, then touch to paper.


Group 2

Group 2

  • Separated first by precipitation as an acid-insoluble chloride.

  • Includes the ions: Hg+2 , Pb+2 , Bi+3 , Cu+2 , and Cd+2

  • Sulfide source is Thioacetamide.


Group 3

Group 3

  • Separated first by precipitation as an alkaline-insoluble sulfide.

  • Includes the ions: Ni+2 , Co+2 , Mn+2 , Zn+2 , Al+3 , Cr+3 , and Fe+3.

  • Also uses Thioacetamide, but under basic (alkaline) conditions.

  • Group 3 also has individual confirmatory tests for each ion.


Group 4

Group 4

  • Separated by precipitation as an insoluble carbonate.

  • Includes the ions Ba+2 , Ca+2 , and Sr+2.

  • Identification includes flame tests for each metal ion.

    • Ba = pale green

    • Ca = orange-red

    • Sr = crimson red


General unknown

General Unknown

  • Lab final will include a General Unknown

  • Will include one ion from EACH group

  • Groups 2 and 3 will be reduced to three ions

  • After precipitation of EACH group, you will need to save the liquid for the next group(s)

  • Any mistakes may mean that you have to start over from the very beginning!

  • You will have a total of three hours to complete both the written and general unknown sections


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