Introduction to qualitative analysis, test for cation using H2S, NaOH and HN4OH, confirmatory test for the cations

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
  • 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 colorless 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:
  1. 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+

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

(d) CO2

  1. Example of cations that gives gas during its confirmatory test is (a) SO32- (b) SO42- (c) CO32-

(d) NH4+

  1. Deep green colour of flame indicate the presence of (a) sodium (b) calcium (c) copper (d) iron
  2. 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 :
  1. 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.

 

 

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