Week 7 – SS3 Second Term Chemistry Notes

 WEEK SEVEN
TOPIC: INTRODUCTION TO QUALITATIVE ANALYSIS

• Introduction to Qualitative Analysis

Test for carbons using H2S, NaOH and NH4OH, Confirmatory Test for the cat ions.

 Introduction to Qualitative Analysis
Qualitative analysis involves examination of colour, flame test, effect of heat and confirmatory test for cat ion and anions.
Cations are metallic ions e,g Ca²⁺, Pb²⁺, Al³⁺, Cu²⁺, Fe²⁺ , Fe³⁺, etc

 Rules in Qualitative Analysis

1. Your test solution should not be diluted too much
2. Use only small quantity of reagents

Examination of colour and physical state of specimen

     Substance         colour            physical state
1.    Sulphur         yellow            solid
2.    Copper(ii)oxide     black            solid
3.    Iodine             dark brown        solid
4.    Nitrogen iv oxide     reddish brown        gas
5.     Mercury         white            liquid

 Flame test

1. Deep green colour of flame indicate the presence of copper
2. Deep yellow colour indicate the presence of sodium
3. Brick red indicate calcium.

 EVALUATION

1. State ten (10) examples of cations
2. Give the colour of the following substance.
   1. Distilled water
   2. Iron filling
   3. Manganese(iv) oxide
   4. Benzoic acid.

 Test for Cations
The Cations are Ca²⁺, Zn²⁺, Al³⁺, Pb²⁺, Fe²⁺. Fe³⁺, Cu²⁺, NH4 ⁺

 Test for Ca²⁺
    Test            Observation            Inferences
Sample + H₂O            dissolve to give a         soluble
                Colourless solution
+ NaOH in drop            white powdery precipitate    
in excess            insoluble in excess        Ca²⁺ present
soln + NH₃ soln            No noticeable reaction        Ca²⁺ present
        
Test for Zn²⁺
Sample + H₂O            dissolve in water to        soluble
                Give a colourless solution
Soln + NaOH in         white gelatinous precipitate    Zn²⁺, pb²⁺,
Drop in excess            soluble in excess        Al³⁺ may be present
Soln +  NH₃ soln        white gelatinous precipitate    
In drop
In excess            ppt soluble in excess        Zn²⁺ present
                Test for Al³⁺
Sample +H₂O            dissolve in water to give    soluble
                a colourless solution
soln + NaOH
in drop                white gelatinous precipitate   Zn²⁺,pb²⁺ Al³⁺ may be
in excess            soluble in excess        present

 Soln + NH₃OH            white gelatinous ppt
In drops
In excess            insoluble in excess         Al³⁺ or pb²⁺

                 Test for Pb²⁺
Sample + H₂O            dissolve in water to give      soluble
                Colourless solution
Soln + NaOH
In drop                 White gelatinous ppt         Zn²⁺,Pb²⁺, Al³⁺
In excess               soluble in excess         may be present
Soln+ NH₃ soln
In drop                    white gelatinous ppt         Al³⁺ or Pb²⁺
In excess               insoluble in excess         may be present
Soln + dil HCl              white ppt                    Pb²⁺ present
Ppt + heat            ppt dissolve when hot and
                Reappear when cool         Pb²⁺ present
Soln + K₂CrO₄             yellow precipitate             Pb²⁺ present

 Test for Fe²⁺
Test            Observation                Inferences
Sample + H₂O        dissolve in water             soluble
Soln +NaOH soln
In drops        dirty green gelatinous ppt         Fe²⁺ present
In excess        insoluble in excess            
Soln +NH₃ in         Dirty green gelatinous
Drop            precipitate                 Fe²⁺ present
In excess        insoluble in excess

 Test for CU²⁺
Test            Observation                Inference
Sample +H₂O        dissolve in water            soluble
Soln +NaOH in
Drops            Blue gelatinous ppt    
In excess        insoluble in excess            Cu²⁺ present
Soln+NH₃ in drop    pale blue gelatinous ppt
In excess        soluble in excess to give a
            Deep blue solution            Cu²⁺ present
            
Test for NH₄⁺
Test            Observation                Inferences
Sample + H₂O        dissolve in water to give a
            Colourless solution            soluble
Soln +NaOH        No ppt, but effervescence occur
In drop + warm     with libration of colourless gas
            with choking smell
Gas + moist        It turns moist red litmus paper    Alkaline gas
Litmus paper        blue.
Gas + con HCl        It gives white fumes with con HCl    NH₃ gas from NH₄⁺

 GENERAL EVALUATION

1. Give the common reagents used for confirmatory test for cations.
2. State the colour of the solution when the sample that contains the following dissolve in water:

a. Fe ²⁺        b. Cu ²⁺        c. Fe ³⁺

 WEEKEND ASSIGNMENT

1. The following give white gelatinous precipitate in NaOH except? (a) Al ₃₊ (b) pb₂₊ (c) CU ₂₊

   (d) Zn₂₊

2. One of the following gives ‘pop’ sound when contact with lighted splint. (a) O₂ (b) H₂ (c ) NH₃

   (d) CO₂

3. Example of cations that gives gas during its confirmatory test is (a) SO₃^2- (b) SO₄^2-    (c) CO₃^2-

   (d) NH₄⁺

4. Deep green colour of flame indicate the presence of (a) sodium (b) calcium    (c) copper (d) iron
5. The only alkaline gas that changes moist red litmus paper to blue is (a)NH₃    (b) HCl    (c) NaOH (d) NH₄OH

 THEORY

1. Explain the confirmatory test for the following cations
2. State the flame test for the following :

a. Calcium    b. Copper     c. sodium     d. iron

 READING ASSIGNMENT
School Chemstry by O.Y Ababio pages 165 – 183
Practical chemistry by R. I. Makanjuola pages 31-36.
Practical Chemistry for Schools and Colleges by Godwin O. Ojokuku pages 30 – 98.