1. Chapter 21
Qualitative Analysis
LEARNING OUTCOMES
 Identify gases – H2, O2, CO2, NH3, SO2, Cl2 and H2O
 Identify cations – Pb2+, Al3+, Ca2+, Zn2+, Fe3+, Fe2+,
NH4+, Cu2+
 Identify anions – CO32-, SO42-, SO32-, NO3-, Br-, I-, Cl-

2. Chapter 21
Qualitative Analysis
What is QA?
 QA stands for Qualitative Analysis.
It is a process that a chemist carries out
to identify an unknown substance.
 The analysis will identify the cation(s)
and anion(s) present in the unknown sample.

3. Chapter 21
Qualitative Analysis
The QA Process
Five important steps
1. Make preliminary observations about the
unknown substance.
2. Carry out tests in the order given.
3. Make observations and record them in a suitable
format.
4. Draw conclusions from the observations
5. Identify the unknown substance.

4. Chapter 21
Qualitative Analysis
Preliminary Observations
What is the nature of the What is the colour of the
substance? substance?
- Is it crystalline, metallic - Is it white, colourless,
or in powder form? blue, yellow or some other
colour?
The colour tells us about the possible cations
present in the substance.

5. Chapter 21
Qualitative Analysis
Preliminary Observations
Colour Possible identity of substance
White (colourless) Sodium (Na+), potassium(K+), ammonium
(NH4+)
Black Copper(II) oxide (CuO),
Iron(II) oxide (FeO)
Blue/green Copper(II), Cu2+ or Iron(II), Fe2+
Yellowish/brown Iron(III), Fe3+
Greyish, metallic Metals: Zinc, Iron, Magnesium,
Aluminium

6. Chapter 21
Qualitative Analysis
Preliminary Observations
Is it soluble in water?
 The solubility tells us about the
Soluble
possible anions present in the
substance.
Insoluble

7. Chapter 21
Qualitative Analysis
Preliminary Observations
Table of Solubility
Salt Solubility in water
Carbonates Insoluble except those of sodium,
potassium and ammonium
Chlorides Soluble except those of lead(II) and
silver.
Nitrates All are soluble.
Sulphates Soluble except those of lead(II) and
Barium

8. Chapter 21
Qualitative Analysis
Quantity of Substance
 Solid : 1 small spatula, just enough
to cover the bottom of a test tube.
 Liquid : About 2 cm-depth in a test tube.
 Reagent : Pour slowly and carefully
down the side of the test tube.
Or
use a dropper and drop it slowly into the test tube.

9. Chapter 21
Qualitative Analysis
Using a Bunsen burner
Heating Liquids
 Use a gentle non-luminous flame (air-hole half open) for
heating a liquid in a test tube.
 Move the test tube up and down the flame and stop the
heating as soon as the liquid starts to boil.
Heating Solids
 When heating a solid, place it in a dry, clean test tube. Heat
gently at first, then strongly.
 For your own safety, wear protective goggles and point the
test tube away from yourself and others when heating.

10. Chapter 21
Qualitative Analysis
Recording Results
 Record all your observations
immediately or you may forget.
 Record the change in colour
Before After
before and after the test.
 Record the formation of a
precipitate - its colour and
whether it is soluble in
excess (extra amount) of
White ppt. Ppt. is
the reagent. formed soluble

11. Chapter 21
Qualitative Analysis
Recording Results
 Record the liberation of a gas by noting if any bubbles
(effervescence) are seen. State the test you carried out to
identify the gas, and the result you obtained.
 You may use phrases and short forms:
formulae for names of chemicals
ppt. for precipitate
aq. for aqueous solution

12. Chapter 21
Qualitative Analysis
Quick Check 1
1. State the colour of the following
substances:
(a) Sodium carbonate: __________
(b) Potassium sulphate: _________
(c) Calcium chloride: ___________
(d) Iron(II) sulphate: ___________
(e) Iron(III) sulphate: ___________
(f) Copper(II) sulphate: _________
(g) Copper(II) carbonate: ________
(h) Copper(II) oxide: ___________
Solution

13. Chapter 21
Qualitative Analysis
Quick Check 1 (cont’d)
2. State whether the following substances are soluble
or insoluble in water:
(a) Sodium carbonate: ________________
(b) Magnesium carbonate: _____________
(c) Calcium chloride: _________________
(d) Zinc sulphate: ____________________
(e) Calcium carbonate: ________________
(f) Lead(II) chloride
(g) Lead(II) nitrate: ___________________
Solution

14. Chapter 21
Qualitative Analysis
Solution to Quick Check 1
1. State the colour of the following substances:
(a) Sodium carbonate: white
(b) Potassium sulphate: white
(c) Calcium chloride: white
(d) Iron(II) sulphate: greenish-yellow
(e) Iron(III) sulphate: reddish-brown
(f) Copper(II) sulphate: blue
(g) Copper(II) carbonate: green
(h) Copper(II) oxide: black
Return

15. Chapter 21
Qualitative Analysis
Solution to Quick Check 1
(cont’d)whether the following substances are soluble or
2. State
insoluble in water:
(a) Sodium carbonate: soluble
(b) Magnesium carbonate: insoluble
(c) Calcium chloride: soluble
(d) Zinc sulphate: soluble
(e) Calcium carbonate: insoluble
(f) Lead(II) chloride: insoluble
(g) Lead(II) nitrate: soluble
Return

16. Chapter 21
Qualitative Analysis
Detection of gases
 How do we tell if a gas is given off?
(a) Effervescence
- Bubbles of gas are seen in
the solution.
(b) Fumes
- White fumes are seen when a
substance is heated.

17. Chapter 21
Qualitative Analysis
Testing for gases
 Note the colour of the gas by
looking through the side of the Look here
test tube above the substance
Not here
or solution.
 Note the smell of the gas by
holding the mouth of the tube a
few cm from the nose and fanning
the gas towards you.

18. Chapter 21
Qualitative Analysis
Testing for gases
Testing with litmus paper
Wet the litmus papers (one piece of
blue and one piece of red) with
distilled water, then hold it near the
mouth of the test tube.
Do not allow the litmus paper to
touch the sides of the test tube or
drop it into the reagent, as it will react
with the reagent and give a false
result.

19. Chapter 21
Qualitative Analysis
Table: Testing for gases
Gas Colour Odour Litmus paper
(moist)
Oxygen Colourless Odourless No effect
Hydrogen Colourless Odourless No effect
Carbon dioxide Colourless Odourless Blue to red
Ammonia Colourless Pungent (like urine) Red to blue
Chlorine Light greenish- Pungent Blue to red then
yellow (Like swimming pool water) white
Sulphur Colourless Pungent Blue to red
dioxide (like burning match)

20. Chapter 21
Qualitative Analysis
Test for gases with lighted splint
Place a lighted (burning)
splint near the mouth of the POP
test tube.
(A) If the lighted splint
extinguishes with a “pop”
sound, then the gas is
hydrogen.

21. Chapter 21
Qualitative Analysis
Test for gases with lighted splint
(B) If the lighted splint burns more
brightly, then the gas may be oxygen.
In this case, you can confirm its identity by
using a glowing splint.
(C) Insert a glowing splint (no fire) into the
mouth of the test tube. If the glowing
splint is relighted (rekindled) and burns
flame
brightly, then the gas is oxygen. extinguished
(D) If the burning splint is extinguished,
then the gas may be carbon dioxide,
water vapour, or some other gases.

22. Chapter 21
Qualitative Analysis
Testing for carbon dioxide
• Pour limewater (calcium hydroxide solution) into a test tube until it
reaches a depth of 2 cm from the bottom of the test tube.
• Stopper the reacting test tube with a delivery tube and pass the
gas into the limewater.
• If a white ppt. is formed, the gas is carbon dioxide.
Note
The carbon dioxide should not be passed for too long, as the
limewater will turn clear again (due to the formation of soluble
calcium hydrogen carbonate), giving a false impression of a
negative test.

23. Chapter 21
Qualitative Analysis
Quick Check 2
Complete the table below.
Test Observation Inference
1. Heat a little of solid X Gas evolved extinguishes a burning
strongly in a test tube. splint. It turns limewater chalky.
2. Heat the solution P gently A pungent gas was given off. It turned
and test for any gas evolved. moist red litmus to blue.
3. Heat solid Q strongly in a A colourless and odourless gas is given
test tube. Test for any gas off. The gas relights a glowing splint.
evolved.
4. Add solid X to the solution Bubbles of gas were given off. The
Z and warm. burning splint is extinguished with a
Test for any gas evolved. “pop” sound.
Solution

24. Chapter 21
Qualitative Analysis
Solution to Quick Check 2
Test Observation Inference
1. Heat a little of solid X Gas evolved extinguished a Gas produced is carbon
strongly in a test tube. burning splint. It turned limewater dioxide.
chalky. CO32- may be present.
2. Heat the solution P A pungent gas was given off. It Gas evolved is NH3.
gently and test for any turned moist red litmus to blue. NH4+ may be present.
gas evolved.
3. Heat solid Q strongly A colourless and odourless gas Gas evolved is oxygen.
in a test tube. Test for is given off. The gas relighted a
any gas evolved. glowing splint.
4. Add solid X to the Bubbles of gas were given off. Gas evolved is hydrogen.
solution Z and warm. Gas extinguished a lighted splint Solid X may be a metal
Test for any gas with a ‘pop’ sound. and solution Z may be an
evolved. acid.
Return

25. Chapter 21
Qualitative Analysis
Identification of cations
Aluminium, Al 3+ Iron(II), Fe2+
Calcium, Ca2+ Iron(III), Fe3+
Zinc, Zn2+ Ammonium, NH4+
Copper(II), Cu2+ Lead(II), Pb2+
 The cations can be identified using sodium hydroxide solution and
aqueous ammonia (ammonium hydroxide).
The cations react with the hydroxide ions in the alkali to form
insoluble metal hydroxides. These hydroxides appear as precipitates.
The cations can be identified from:
(a) the colour of the precipitate,
(b) the solubility of the precipitate in excess of the reagent.

26. Chapter 21
Qualitative Analysis
Identification of cations
 The unknown substance must be in solution form.
If not, a solution must be made as follows:
- soluble salt : dissolve in distilled water.
- insoluble salt : dissolve in a little dilute nitric acid.
Test using sodium hydroxide solution:
Ppt.
(a) Add sodium hydroxide solution drop formed
by drop to the unknown solution.
(b) Observe the precipitate formed and
note its colour.
(c) Add more sodium hydroxide solution (excess).
Shake the test tube and examine whether the precipitate
dissolves in excess sodium hydroxide solution. Colourless/
soluble

27. Chapter 21
Qualitative Analysis
Identification of cations
d) If no precipitate is formed, warm the
mixture and test for ammonia gas.
 Ammonia gas has a pungent
smell (like urine) and turns moist
red litmus paper blue.
 This confirms the presence of
ammonium ion (NH4+) in the
unknown.

28. Chapter 21
Qualitative Analysis
Test for cations (Table 1)
Cation Add a little NaOH (aq) Add excess NaOH (aq)
Al 3+ White ppt ppt. dissolves to form colourless solution
Ca 2+ White ppt ppt. remains insoluble
Zn 2+ White ppt ppt. dissolves to form colourless solution
Pb 2+ White ppt ppt. dissolves to form colourless solution
Cu 2+ Blue ppt ppt. remains insoluble
Fe 2+ Dirty-green ppt ppt. remains insoluble (turns brown on
standing)
Fe 3+ Reddish-brown ppt ppt. remains insoluble
NH4 + No ppt. When warmed, No change
NH3 gas given off.

29. Chapter 21
Qualitative Analysis
Identification of cations (using aq. NH3)
Test using aqueous ammonia:
(a) Add ammonia solution drop by drop
to the unknown solution.
(b) Observe the precipitate formed and
note its colour. Ppt.
formed
(c) Add more ammonia solution (excess).
Shake the test tube and examine
whether the precipitate dissolves in
excess ammonia solution.
Colourless/
soluble

30. Chapter 21
Qualitative Analysis
Test for cations (Table 2)
Cation Add a little NH3 (aq) Add excess NH3(aq)
Al3+ White ppt. Ppt. remains insoluble
Ca2+ No ppt (or very slight ppt.) No change
Zn2+ White ppt. Ppt. dissolves to form colourless solution
Pb2+ White ppt. Ppt. remains insoluble
Cu2+ Blue ppt. Ppt. dissolves to form dark blue solution.
Fe2+ Dirty-green ppt. Ppt. remains insoluble (turns brown on
standing)
Fe3+ Reddish-brown ppt. Ppt. remains insoluble
NH4+ No ppt. No change

31. Chapter 21
Qualitative Analysis
Quick Check 3
1. What are some of the preliminary observations that you can make on an
unknown sample, before carrying out any test?
2. When a solid is insoluble in water, what acid is used? Why?
3. Which cations will produce a white precipitate with sodium hydroxide solution
and aqueous ammonia?
4. Which cation will produce a white precipitate which is soluble in both aqueous
ammonia and sodium hydroxide?
5. Which cations will produce a white precipitate which is soluble in excess
sodium hydroxide, but not in excess aqueous ammonia?
6. Which cation will produce a white precipitate with sodium hydroxide solution
but not with aqueous ammonia?
7. Which cation will produce a blue precipitate with sodium hydroxide? Solution
8. Which cation will produce a deep blue solution with aqueous ammonia?

32. Chapter 21
Qualitative Analysis
Solution to Quick Check 3
1. Observe the colour and texture of the unknown
sample, and determine if it is soluble in water.
2. Dilute nitric acid is used to dissolve the solid
because nitrates of all metals are soluble in water.
3. Aluminium, lead and zinc ions
4. Zinc ions
5. Aluminium and lead ions
6. Calcium ion
7. Copper(II) ion Return
8. Copper(II) ion

33. Chapter 21
Qualitative Analysis
Identification of Anions
Carbonate, CO32- Chloride, Cl-
Iodide, I- Sulphate, SO42 -
Nitrate, NO3-
 Each anion has a different specific test.
 For carbonate, you need not make a solution to carry out the test.
For other anions, you must make a solution of the unknown in distilled
water only.
*If you use dilute nitric acid to dissolve it, you are introducing the nitrate ions
into the unknown.

34. Chapter 21
Qualitative Analysis
Test for carbonate
Test Observation Inference
 Add some dilute  Bubbles of gas are The gas is CO2 .
hydrochloric acid (or given off. Therefore, CO32-
nitric acid) to the  The gas turns
is present in the
unknown. limewater chalky. unknown.
 Pass the gas into
limewater.

35. Chapter 21
Qualitative Analysis
Test for chloride
Test Observation Inference
 Add a little silver  A white ppt is White ppt is AgCl.
nitrate solution to formed.
the unknown.  White ppt is
Therefore, Cl- is
 Add dilute nitric insoluble in nitric acid. present.
acid to the above,
then shake.

36. Chapter 21
Qualitative Analysis
Test for iodide
Test Observation Inference
 Add a little lead(II)  A yellow ppt is Yellow ppt is PbI2.
nitrate solution to the formed. Therefore, I- is
unknown.  Yellow ppt is insoluble present in the
 Add dilute nitric in nitric acid. unknown.
acid to the above,
then shake.

37. Chapter 21
Qualitative Analysis
Test for sulphate
Test Observation Inference
 To the unknown  A white ppt is White ppt is
solution, add a little formed. BaSO4.
barium chloride (or  White ppt is Therefore, SO42-
barium nitrate) insoluble in is present in the
solution. hydrochloric acid unknown.
 Then add some (or nitric acid).
dilute hydrochloric acid
(or nitric acid) and
shake.

38. Chapter 21
Qualitative Analysis
Test for nitrate
Test Observation Inference
 To the unknown, add a
little sodium hydroxide
solution.  A pungent gas is NH3 gas is
Then add a few pieces of given out. produced.
aluminium foil (or a  The gas turns moist
spatula of aluminium NO3- is present in
red litmus paper blue. the unknown.
powder).
 Warm the mixture
gently.
 Test for ammonia gas
evolved.

39. Chapter 21
Qualitative Analysis
Summary of Tests for Anions (Table 3)
Anion Test Observation
Carbonate, Add dilute HCl. Test for gas Effervescence. Gas evolved
CO32- evolved. turned limewater chalky.
Chloride, Add AgNO3 solution, White ppt. insoluble in HNO3
Cl- followed by dilute HNO3
Iodide, Add Pb(NO3)2 solution, Yellow ppt. insoluble in HNO3
I- followed by dilute HNO3
Sulphate, Add BaCl2 solution, White ppt. insoluble in HCl
SO42- followed by dilute HCl.
Nitrate, Add NaOH solution, then Al foil. NH3 gas evolved turned red
NO3- Warm gently. litmus blue

40. Chapter 21
Qualitative Analysis
Quick Check 4
1. When we add aqueous silver nitrate to an unknown, what anion(s) are we
looking for?
2. When we add aqueous barium chloride or barium nitrate to an unknown,
what anion(s) are we looking for?
3. When we are told to add dilute hydrochloric acid to an unknown, what
anion are we testing for and what should we get ready?
4. When we are told to add sodium hydroxide and aluminium powder to an
unknown solution, what anion are we testing for and what should we get
ready?
5. When we add silver nitrate or barium chloride solution to an unknown,
what reagent should we also add? What is the reason for this?
Solution

41. Chapter 21
Qualitative Analysis
Solution to Quick Check 4
1. Chloride, Cl- or iodide, I-
2. Sulphate, SO42-
3. Carbonate, CO32-. We should get a delivery tube and test tube
containing some limewater ready.
4. Nitrate, NO3-. We should get a piece of moist red litmus paper
ready.
5. We should add some dilute nitric acid. This is to exclude any
carbonate present from forming a precipitate.
Return

42. Chapter 21
Qualitative Analysis
Quick Check 5
Complete the table below and identify the substance S1.
Test Observation Inference
1. Dissolve a sample of S1 in distilled S1 dissolved to form a pale blue
water and divide it into 3 portions. solution.
2. To the first portion, add aqueous A blue ppt was formed.
sodium hydroxide slowly until in excess. Ppt was insoluble in excess NaOH.
3. To the second portion, add aqueous A blue ppt was formed.
ammonia slowly until in excess. Ppt dissolved to form a deep blue
solution.
4. To the third portion, add barium chloride A white ppt was formed.
solution, then dilute HCl. Ppt was insoluble in HCl.
Conclusion: S1 is _________ . Solution

43. Chapter 21
Qualitative Analysis
Solution to Quick Check 5
Complete the table below and identify the substance S1.
Test Observation Inference
1. Dissolve a sample of S1 in distilled S1 dissolved to form a pale blue Cu2+ may
be present
water and divide it into 3 portions. solution.
2. To the first portion, add aqueous A blue ppt was formed. Cu2+ is
present.
sodium hydroxide slowly until in excess. Ppt was insoluble in excess NaOH.
3. To the second portion, add aqueous A blue ppt was formed. Cu2+ is
confirmed.
ammonia slowly until in excess. Ppt dissolved to form a deep blue
solution.
4. To the third portion, add barium A white ppt was formed. SO42- is
chloride solution, then dilute HCl. present.
Ppt was insoluble in HCl.
Conclusion: S1 is copper(II) sulphate. Solution