Test for Anions

Identification of gases e.g CO2, SO2 and O2. Characteristics test for anions e.g SO42-,SO32-,CO32-,NO-3, Cl, etc. The anions are negatively change ions examples of anions are SO42-,SO32-,CO32-,S2- etc.


Identification of Gases

Gases               identification

  1. H2 It gives a ‘pop’ sound when the gas is contact with a lighted splint.
  2. O2             It rekindles a glowing splint.
  3. CO2 It is colourless and odourless. It turns lime water milky.
  4. Cl2             A green wish yellow gas, it turns moist iodide paper black.
  5. SO2 Colourless gas with irritating smell. It turns damp blue litmus paper to red. That

is acidic gas.



  1. State two (2) examples of anions with their gases.
  2. Identify Cl2 and NH3


Test For Anions

Test for SO42-

Test                             Observation                                          Inferences

Sample +H2O                dissolve in water                                   soluble

Soln +Bacl2+                  white ppt                                              SO42-, SO32-,CO32-

Dil HCl                         ppt insoluble                                         SO42-, confirmed.

Soln + dil HCl               No visible reaction                               SO32-,CO32-,S2- are absent

Soln + Bacl2                  white precipitate                                  SO42-, confirmed


Test for SO32-

Soln+Bacl2                    white precipitate

+ dil HCl                       dissolve in dil HCl                                 SO32- or CO32-

soln+acidified               decolourise the purple

soln  of KMnO4 colour to colourless                              SO32- confirmed

soln +                            the orange colour change                     SO32- confirmed

acidified K2Cr2O7                   to green (reducing property)


Test for CO32-

Soln+dil HCl                 Effervescence occurred and a             SO32-,CO32-, S2-

Colourless gas is librated                      may be present

Gas+litmus paper          it changes moist blue litmus paper        acidic gas

To red.

Gas + lime water           The gas turned lime                              gas is CO2 from CO32-

Water milky.


Test for S2-

Test                             Observation                                          Inferences

Soln + dil HCl               A colourless gas evolved                       H2S gas from S2-

With rotten egg smell

Gas +KMnO4 soln           purple colour is decolourised

With a deposit of sulphur                    S2- present


Test for Cl

Soln + dil HNO3                        No visible reaction                    SO32- or CO3 are absent

Soln + AgNO3                                       white precipitate                      Cl- present



  1. Give the common reagents for confirmatory test of anions
  2. State how you would confirm/test for NO3-
  3. Name three gases that are colourless and acidic to litmus.
  4. Sodium chloride and silver trioxonitrate(V) crystals are separately soluble in water to give colourless solutions. Explain what happens when their solutions are mixed together.



School Chemstry by O.Y Ababio pages 165 – 183

Practical Chemistry by R. I Makanjuola pages 27-33.

Practical Chemistry for Schools and Colleges by Godwin O. Ojokuku pages 30 – 98.



  1. Brown ring test is used to confirm (a) S2- (b)NO3- (c) SO42- (d) SO32-
  2. The presence of SO32- change the colour of acidified K2Cr2)7 from (a) green to red (b) purple to colourless  (c) orange to green  (d) green to orange
  3. A greenish yellow gas that change moist iodide paper black is (a) Cl2 (b) SO2 (c) H2  (d) O2
  4. Sometimes in the presence of conc HsSO4, copper turning and heat NO3- gives (a) brown ring reaction  (b) pure brown fume   (c ) reddish brown   (d) effervescence
  5. The gas that turns lime water milky is (a) H2 (b) SO2 (c) NH3 (d) CO2.



  1. State the colour of these solutions a. KMnO4 K2Cr2O3 c. HOBr d. CuSO4.5H2O e. Ca(OH)2
  2. Carry out the following exercises on sample K. add about 10cm3 of distilled water to K in a test tube. Divide the solution into four.
  3. To the 1st portion add NaOH drop wise and in excess.
  4. To the 2nd portion add NH3 solution drop wise and then in excess.
  5. To the 3rd portion, add it drops of BaCl2 follow by the addition of dil HCl
  6. To the 4th portion, add dil HCl follow by the addition of BaCl2.

Record your observation and inferences then name the salt K.


See also






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