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
- H2 It gives a ‘pop’ sound when the gas is contact with a lighted splint.
- O2 It rekindles a glowing splint.
- CO2 It is colourless and odourless. It turns lime water milky.
- Cl2 A green wish yellow gas, it turns moist iodide paper black.
- SO2 Colourless gas with irritating smell. It turns damp blue litmus paper to red. That
is acidic gas.
- State two (2) examples of anions with their gases.
- 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
Gas + lime water The gas turned lime gas is CO2 from CO32-
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
- Give the common reagents for confirmatory test of anions
- State how you would confirm/test for NO3-
- Name three gases that are colourless and acidic to litmus.
- 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.
- Brown ring test is used to confirm (a) S2- (b)NO3- (c) SO42- (d) SO32-
- 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
- A greenish yellow gas that change moist iodide paper black is (a) Cl2 (b) SO2 (c) H2 (d) O2
- 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
- The gas that turns lime water milky is (a) H2 (b) SO2 (c) NH3 (d) CO2.
- State the colour of these solutions a. KMnO4 K2Cr2O3 c. HOBr d. CuSO4.5H2O e. Ca(OH)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.
- To the 1st portion add NaOH drop wise and in excess.
- To the 2nd portion add NH3 solution drop wise and then in excess.
- To the 3rd portion, add it drops of BaCl2 follow by the addition of dil HCl
- To the 4th portion, add dil HCl follow by the addition of BaCl2.
Record your observation and inferences then name the salt K.