Qualitative Analysis SS3 Chemistry Lesson Note

SPECIFIC OBJECTIVES: At the end of the lesson, pupils should be able to

1. identify ions in solution.
2. Test for simple gases like NH3, NO3, Oxygen etc

INSTRUCTIONAL TECHNIQUES: 

• Identification, 
• explanation, 
• questions and answers,
• demonstration, 
• videos from the source

INSTRUCTIONAL MATERIALS: 

• Videos, 
• loudspeaker, 
• textbook, 
• relevant salts, 
• acids, 
• bases, 
• starch, etc.

NOTE

Qualitative analysis involves the examination of colour, flame test, the effect of heat and confirmatory test for cation 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 a small quantity of reagents

Examination of colour and physical state of the 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 indicates the presence of copper
2. Deep yellow colour indicates the presence of sodium
3. Brick red indicates calcium.

Evaluation

1. State ten (10) examples of cations
2. Give the colour of the following substance.

• Distilled water
• Iron filling
• Manganese(iv) oxide
• Benzoic acid.

Test for cations

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

Alkaline gas

Gas + con HCI It gives white fumes with conc HCI NH₃ gas from NH₄⁺

General evaluation

1. Give the common reagents used for the confirmatory test for cations.
2. State the colour of the solution when the sample that contains the following dissolves in water: a. Fe ²⁺ b. Cu ²⁺ c. Fe ³⁺

Weekend assignment

1. The following gives a white gelatinous precipitate in NaOH except? (a) Al ³⁺ (b) pb²⁺ (C) CU²⁺ (d) Zn²⁺
2. One of the following gives a ‘pop’ sound when in contact with a lighted splint. (a) O₂ (b) H₂ (c) NH₃ (d) CO₂
3. Example of cations that give gas during their confirmatory test is (a) SO₃^2- (b) SO₄^2- (c) CO₃^2- (d) NH₄⁺
4. Deep green colour of the flame indicates 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 Chemistry 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.