QUALITATIVE ANALYSIS
Name of teacher:
Week: Date: Time:
Period: Duration: 1 HR 20 MIN. Average age of learners: 16YEARS
Subject: CHEMISTRY Class: SS THREE
Topic: QUALITATIVE ANALYSIS
Sub topic:
Reference materials:
(1) ESSENTIAL CHEMISTRY, TONALD PUBLISHERS, I. O ODESINA
(2) NEW SCHOOL CHEMISTRY, AFRICAN FIRST PUBLISHERS, OSEI YAW ABABIO
(3) INTERNET
Instructional materials: beaker, beam balance
Entry behavior: The students have been taught density.
Objective: At the end of the lesson the students should be able to:
1. Identify salt with their appearance
2. Identify ions with flame test
3. Explain test for gases
4. State the reagents used in test for cations and anions.
5. Explain test for organic compound.
CONTENT
QUALITATIVES ANALYSIS
In qualitative analysis, we
identify the elements and compounds that are present in a sample of a given
substances.
The preliminary test we carried out under the
following headings:
1.
Appearance of the compound
(colour) 2. Flame Test 3. Action of Heat (Identification of
gases).
|
APPEARANCE |
PROBABLE SALT / COMPOUND |
|
Green
|
Iron(ii)
salts, Iron (iii) salt are usually pale green |
|
Yellow/
brown |
Lead(ii)oxide,
iron(iii) salt solution, candium sulphide yellow |
|
Black
or red |
CuO,
PbS, CuS, Ag2S, HgS |
|
White
colourless |
Ca2+,
Pb2+, NH4+, Na+, Al3+,
Zn2+ salts and ZnS, MnS |
|
Smell
of NH3 |
Ammonium
salt |
|
Smell
of sulphur |
Trioxosulphate
(iv) salts |
|
Smell
of H2S |
Sulphides
|
|
Deliquescent |
Chloride
or trioxonitrate (v) |
FLAME TEST
|
COLOUR FROM FLAME TEST |
PROBABLY ION |
|
Brick
red |
Ca2+ |
|
Deep
green |
Cu2+
|
|
Blue
|
Pb2+ |
|
Persistence
golden yellow |
Na+ |
|
Persistence
lilac |
K+ |
|
Persistence
light green |
Ba2+ |
GASES EVOLVED ON HEATING
|
GAS |
INFERENCE |
|
NO2 |
NO3- |
|
CO2 |
CO32-
OR HCO3- |
|
O2 |
NO3- |
|
SO2 |
SO32- |
|
NH3 |
NH4+ |
ACTION OF HEAT ON SPECIMEN
|
OBSERVATION |
INFERENCE |
|
White
when cold and yellow when hot |
Zn2+
(ZnO) present |
|
Yellow
when cold and reddish brown when hot |
Pb2+
(PbO) |
|
Reddish-brown |
Fe3+
(Fe2O3) |
|
Water
vapour which condenses at the upper part of the tube |
Hydrated
salts HCO3- or OH- present. |
|
White
sublimate |
Ammonium
salt |
TEST FOR
GASES
|
GAS |
COLOUR/SMELL |
TEST |
RESULT
IF POSITIVE |
|
Cl2 |
Greenish-yellow, pungent |
a. Moist blue / litmus paper. b. Bubble through bromine solution |
Turns red then bleaches it (acidic) Bromine is liberated and solution turns
yellow or orange. |
|
NO2 |
Reddish-brown, pungent |
a. Moist blue litmus paper b. Bubble through fresh FeSO4
solution |
Turn red (acidic) Solution turns blue |
|
NH3 |
Colourless pungents smell like that of urine |
a. moist red litmus paper b. bring in contact with drop of conc. HCl
on a glass rod. |
Turns blue (alkaline gas) White dense fumes due to the presence of NH4Cl |
|
H2S |
Colourless, rotten egg smell |
Moist lead(ii) ethanoate paper |
Turns black |
|
HCl |
Colourless |
a. damp blue litmus paper. b. blows across mouth of test tube c. bring in contact with drop of NH3
solution on a glass rod |
Turns red (acidic) Copious fuming White dense fume of ammonium chloride. |
|
CO2 |
Colourless, odourless |
a. damp blue litmus paper b. bubble through lime water in excess of
it. |
Turn red (acidic) Turns milky (ppt of CaCO3) milky
colour disappears due to formation of CaHCO3 |
|
H2 |
Colourless, odourless |
a. damp blue and red litmus paper b. lighted splint |
No effect (neutral gas) Little explosion occurs giving pop sound;
burns with blue flame, it mixed with air |
|
O2 |
Colourless, odourless |
a. damp blue and red litmus paper |
No change (neutral) |
|
H2O |
Colourless, odourless |
a. damp blue or red litmus paper b. anhydrous CuSO4 (white in
colour) |
No change (neutral gas) It turns to blue crystal of CuSO4.5H2O |
|
SO2 |
Colourless, pungent smell |
a. damp blue litmus paper b. bubble through K2Cr2O7
acidified with dilute H2SO4 c. bubble through KMnO4 solution
acidified |
Turn red (acidic) Turn from orange to green Turn from purple to colourless (reducing
agent) |
Note: H2S gives the same result
with K2Cr2O7 and KMnO4 all
acidified but there will be yellow deposit of sulphur.
TEST FOR
CATION
Cation Reaction
with
|
cation |
Dil.HCl |
Dil.
H2SO4 |
Dil.
NaOH |
Dil.
NH3 |
NH4Cl
+ Dil NH3 |
H2S |
H2S/Dil
HCl |
|
Pb2+ |
White crystalline ppt dissolving when
warmed, reappears on cooling |
White powdered ppt |
White powdered ppt soluble in excess |
White powdered ppt insoluble in excess |
White crystalline ppt on adding NH4Cl |
Black ppt |
Black ppt |
|
Al3+ |
No ppt |
No ppt |
White gelatinous ppt soluble in excess
reagent |
White gelatinous ppt insoluble in excess
reagent |
White gelatinous ppt. |
No ppt |
No ppt |
|
Zn2+ |
No ppt |
No ppt |
White gelatinous ppt soluble in excess
reagent |
White gelatinous ppt soluble in excess
reagent |
No ppt |
White ppt |
No ppt |
|
Ca2+ |
No ppt |
No ppt (may leave slightly turbidity) |
White powdered ppt insoluble in excess NaOH |
No ppt turbidity due to CO3 in
reagent |
No ppt |
No ppt |
No ppt |
|
Fe2+ |
No ppt |
No ppt |
Dirty green gelatinous ppt insoluble in
excess reagent |
Dirty green gelatinous ppt insoluble in
excess reagent |
Dirty green gelatinous ppt. |
Slight ppt or non |
No ppt |
|
Fe3+ |
No ppt |
No ppt |
Reddish- brown gelatinous ppt insoluble in
excess reagent |
Reddish-brown gelatinous ppt insoluble in
excess reagent |
Reddish-brown gelatinous ppt. |
Yellow to pale-green with yellow deposit |
Yellow to pale-green with yellow deposit |
|
Cu2+ |
No ppt |
No ppt |
Light-blue gelatinous ppt. in excess reagent |
Light blue gelatinous ppt soluble in excess
giving deep blue solution. |
Light blue
ppt which dissolves in excess giving a deep blue solution |
Black ppt |
Black ppt |
CONFIRMATION
TEST FOR CATIONS
|
TEST |
OBSERVATION |
INFERENCE |
|
1. To the aqueous solution, add (NH4)2CO3
or ammonium oxalate |
White ppt |
Ca2+ confirmed |
|
2. To an aqueous solution is added NH3
sol. And NH4Cl solution |
White ppt |
Al3+ confirmed |
|
3. a. To an aqueous solution add K2Cr2O4 b.
solution KI |
Yellow ppt Yellow ppt |
Pb2+ present Pb2+ present |
|
4. a. To the solution add potassium
hexacyanoferrate(ii) solution K4Fe(CN)6 aq
b. To the solution add potassium hexacyanoferrate(iii) solution K3Fe(CN)6
aq |
Light blue ppt Deep blue ppt |
Fe2+ present Fe2+ present |
|
5. a. To the specimen solution add K4Fe(CN)6
b. To the specimen solution
add thiocyannate solution KSCN or ammonium thiocyanate solution. |
Deep blue ppt. Deep blood red colouration |
Fe3+ present. Fe3+ present. |
|
6. specimen solution + potassium
hexacyanoferrate (ii) solution K4Fe(CN)6 |
Brown ppt |
Cu2+ present. |
|
7. a. To the solution add (NH4)2S
solution or H2S b.
To the solution add K4Fe(CN)6 |
Dirty white ppt. White ppt. |
Zn2+ present. Zn2+ present. |
|
8. warm solution gently with slightly excess
of NaOH aq |
Gas evolved turned red litmus blue. |
NH4+ present. |
TEST FOR
ANION
|
TEST |
OBSERVATION |
INFERENCE |
|
1. a. To the solution add AgNO3 + dil. NH4OH
in excess
b. Salt solution + HNO3 + AgNO3 to the mixture
in (a) above + NH4OH in excess.
c. To a salt sample add MnO2 and Conc. H2SO4
and warm gently |
White ppt. White ppt dissolves. White ppt. insoluble in NHO3,
white ppt dissolves. Greenish yellow gas with suffocation odour
and turns damp blue litmus paper red
finally bleaches it. |
Cl- present. Cl- confirmed. Cl- present. Cl- present. Cl- present. The gas is Cl2(g) |
|
2. To the salt solution add dil. HCl or
Conc. H2SO4 and warm gently. |
Greenish yellow gas with suffocation odour
and turns dump blue litmus paper red and finally bleaches it. |
The gas is CO2. CO32-
or HCO3- present. |
|
3. To the salt solution add BaCl2
solution and then add few drops of hydrogen chloride solution. Or Salt solution + Ba(NO3)aq + dil.
HNO3 Salt solution + acidified dil. K2Cr2O7 To about 2cm3 of the clear
solution add about 3cm3 of freshly prepared FeSO4, then
add about 3cm3 of Conc. H2SO4 slowly down
the side of the test tube held in a slanting position. Or Salt solution + Conc. H2SO4 |
White ppt. which does not dissolve in
presence of HCl acid. White ppt. soluble in excess dil. HCl White ppt. insoluble in dil. HNO3 White ppt. soluble in dil. HNO3. The orange colour of K2Cr2O7
turns green. A brown ring is formed at the junction of
the two layers. Reddish-brown fumes evolved |
SO42- present. SO32- present. SO42- present. SO32- present. SO32- present. NO3- confirmed, the
brown ring is due to the formation of FeSO4. NO, NO3- present. |
TEST FOR ORGANIC COMPOUND
|
TEST |
OBSERVATION |
INFERENCE |
|
1. TEST
FOR STARCH (C5H10O5)n a. Into a test-tube containing suspected
starch solution, add iodine solution (KI/I2). b. In a test-tube containing suspected
starch solution, add iodine solution, warm and cool. |
Blue- black colouration observed. Blue-black colouration disappeared when
warmed and reappeared on cooling. |
Starch confirmed. Starch confirmed. |
|
2. TEST
FOR REDUCING SUGAR (GLUCOSE
AND FRUCTOSE) a. Into a test-tube containing suspected
reducing sugar solution, add Fehling’s solution and warm in water bath. |
Red precipitate observed |
Reducing sugar confirmed. |
|
3. TEST
FOR NON-REDUCING SUGAR (COMPLEX
SUGAR) a. Into a test-tube containing suspected
non-reducing sugar solution add dil. HCl and warm for 3-5 minutes. Now cool
the tube; neutralize the excess acid, with NaOH or Na2CO3
solution (test with litmus paper). Now add few drop of Fehling solution and
warm in water bath. |
Red precipitate observed |
Non-reducing sugar confirmed. |
|
4. TEST
FOR PROTEINS a. To a solution or substance, suspected to
be protein, add soda lime solution, heat the mixture in boiling tube. b. To a solution or substance suspected to
be protein, add 3cm3 of NaOH sol. Then add 1-2 drops of CuSO4 |
A gas is given off having pungent smell,
turn red litmus paper blue and form dense white fumes with drop of HCl solution.
The gas is NH3. A purple colour observed |
Protein is confirmed. Protein is confirmed. |
|
5. TEST
FOR FATS AND OILS a. Press substance suspected to be fats and
oils on a filter paper or plain sheet of paper b. Add a few drops of liquid suspected to be
oil on a filter paper or plain sheet c. Add equal amount of 5ml of NaOH in a
liquid suspected to be oil or solid substance suspected to be fat. Heat while
stirring or shaking the test-tube. Precipitate is filtered. Residue +
distilled water, shake. |
The area of the paper turns translucent i.e
light compass through it. The region where the liquid touches diffuses
and turns the paper translucent. Oil turns cloudy on addition of reagent, on
heating, a mass of white ppt is produced which could be a product of
saponification. A lather is produced indicating the white ppt is a soap |
Fats or Oil confirmed. Oil is confirmed. Oil is confirmed. |
PRESENTATION
Step I: The teacher explains how to identify salt with their
appearance.
Step II: The teacher explains test for ions with flames.
Step III: The students chorus test for ion using flame test.
Step IV: The teacher leads the students to test for cations and
anions.
Step V: The teacher explains test for organic compound.
Step V: The teacher allows the students to ask questions.
EVALUATION
The teacher asks the following questions:
1. Identify salt with their appearance
2. Identify ions with flame test
3. Explain test for gases
4. State the reagents used in test for cations and anions.
5. Explain test for organic compound.
ASSIGNMENT
1a. Give one chemical
test to distinguish between CH3CH2OH and CH3COOH.
b. State what is
observed when aqueous ammonia is added to :
i. litmus paper
ii. Pb(NO3)2 solution in drops until in
excess
iii. Freshly
precipitated AgCl in excess.
b. State what would be observed: I. if a fresh
precipitate of silver chloride was
(i) expose to light
(ii) shake with excess
aqueous ammonia.
II. On bubbling chlorine
through a solution of potassium bromide.
C. A given
crystalline solid is suspected to be either sodium chloride or ammonium
tetraoxosulphate (vi). Describe how you would
use the indicator to identify the solid.
2a. When a drop of
concentrated trioxonitrate (v) acid was added to potassium iodide solution, a
violet-coloured gas was evolved.
i.
What is the name of the gas
evolved
ii. State the
functions of concentrated trioxonitrate (v) acid in the reaction.
iii. What would be
observed if starch solution were added to the reaction mixture?
b. I. What technique would you use to purify a
sample of sodium chloride contaminated with ammonium chloride?
II. Given sodium
hydroxide solution, outline the procedure you would use to determine whether or
not all the ammonium chloride in b(I) above
had be removed.
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