Week 8 – SS3 Second Term Chemistry Notes

 WEEK EIGHT
Test for Anions,
Identification of gases e.g CO₂, SO₂ and O₂.
Characteristics test for anions e.g SO₄^2-,SO₃^2-,CO₃^2-,NO^-3, Cl^–, etc.
The anions are negatively change ions examples of anions are SO₄^2-,SO₃^2-,CO₃²-,S^2- 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.

 EVALUATION

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

 Test For Anions
Test for SO₄^2-
Test            Observation                Inferences
Sample +H₂O        dissolve in water            soluble
Soln +Bacl₂+        white ppt                SO₄^2-, SO₃^2-,CO₃^2-
Dil HCl         ppt insoluble                SO₄^2-, confirmed.
Soln + dil HCl        No visible reaction            SO₃^2-,CO₃^2-,S^2- are absent
Soln + Bacl₂        white precipitate            SO₄^2-, confirmed

 Test for SO₃^2-
Soln+Bacl₂        white precipitate
+ dil HCl        dissolve in dil HCl            SO₃^2- or CO₃^2-
soln+acidified        decolourise the purple
soln of KMnO₄    colour to colourless            SO₃^2- confirmed
soln +            the orange colour change        SO₃^2- confirmed
acidified K₂Cr₂O₇    to green (reducing property)    

Test for CO₃^2-
Soln+dil HCl        Effervescence occurred and a         SO₃^2-,CO₃^2-, S^2-
            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 CO₃^2-
            Water milky.

Test for S^2-
Test         Observation                Inferences
Soln + dil HCl        A colourless gas evolved        H₂S gas from S^2-
            With rotten egg smell
Gas +KMnO₄ soln    purple colour is decolourised
            With a deposit of sulphur        S^2- present

Test for Cl^–
Soln + dil HNO₃    No visible reaction        SO₃^2- or CO₃ are absent
Soln + AgNO₃        white precipitate        Cl- present

GENERAL EVALUATION

1. Give the common reagents for confirmatory test of anions
2. State how you would confirm/test for NO^3-
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.

 READING ASSIGNMENT
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.

 WEEKEND ASSIGNMENT

1. Brown ring test is used to confirm (a) S^2- (b)NO^3- (c) SO₄^2- (d) SO₃^2-
2. The presence of SO₃^2- 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 NO^3- 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.

 THEORY

1. State the colour of these solutions a. KMnO₄ b. 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.
   1. To the 1^st portion add NaOH drop wise and in excess.
   2. To the 2^nd portion add NH₃ solution drop wise and then in excess.
   3. To the 3^rd portion, add it drops of BaCl2 follow by the addition of dil HCl
   4. To the 4^th portion, add dil HCl follow by the addition of BaCl₂.

Record your observation and inferences then name the salt K.