GUIDED QUALITATIVE ANALYSIS
- You are provided with sample Y containing one cation and one anion. Carry out the guided systematic procedure in the Table to identify the cation and anion present in the sample Y.
Table
| S/N | Experiments | Observation | Inference |
| (a) | Observe sample Y. | ||
| (b) | Heat sample Y in a dry test tube. | ||
| (c) | Prepare a stock solution of sample Y. Divide the resulting solution into six portions then add: | ||
| (i) Dilute HCl solution in small quantities then in excess to the first portion. | |||
| (ii) small amount of concentrated H2SO4 to the second portion then warm. | |||
| (iii) NaOH solution to the third portion drop – wise till excess. | |||
| (iv) dilute NH4OH in small amount then in excess to the fourth portion. | |||
| (v) FeSO4 solution followed by H2SO4 to the fifth portion. | |||
| (vi) KI solution to the sixth portion, warm then cool the mixture. |
Conclusion
- (i) Cation present in Y is _______________. (ii) Anion present in Y is _______________.
- The chemical formula for Y is ________.
- Name the compound Y
- Write the equation for the reactions that took place at experiments (b) and (c) (ii).
- State two chemical properties of the sample Y.
- Give two uses of the metal present in the sample Y.
- Give three uses of the sample.
SOLUTION
Experimental table
| S/N | Experiments | Observation | Inference |
| (a) | Sample Y was observed.
(i) Colour
|
White colour was observed
|
NH4+, Na+, Ca2+, Zn2+, Pb2+ may be present Or Transition metals Fe2+, Fe3+, Cu2+ may be absent |
|
(ii) Texture
|
Crystalline form was observed. |
NO−3 , SO24−, Cl− may be present
|
|
| (b) | Sample Y in a dry test tube was heated.
|
Reddish brown fumes evolved which turn moist blue litmus paper red and a gas which rekindles a glowing wooden splint was observed.
|
NO−3 may be present
|
| Cracking sound with brown gas was observed. | NO−3 of Pb2+ may be present
|
||
|
Residue reddish brown when hot and yellow when cold was observed.
|
Pb2+ may be present
|
||
| (a) | A stock solution of sample Y was prepared, then the resulting solution was divided into six portion, then;-
(i) To the first portion, dilute HCl solution was added in small quantities then in excess |
No gas evolved |
SO24−, NO−3 , Cl− may be present |
|
White precipitate was observed
|
Pb2+ may be present |
||
| (ii) To the second portion, small amount of concentrated H2SO4 was added then warmed. | Brown fumes evolved which turn moist blue litmus paper red and intensify on addition of copper turnings. | NO−3 may be present | |
| (iii) To the third portion, NaOH solution was added drop – wise till excess. | White precipitate was formed soluble in excess. | Zn2+, Pb2+ may be present | |
| (iv) To the fourth portion, dilute NH4OH was added in small amount then in excess. | White precipitate was formed insoluble in excess. | Pb2+ may be present
|
|
| (v) To the fifth portion, FeSO4 solution was added followed by
H2SO4 |
Brown ring was formed at the junction of the liquids. | NO−3 confirmed | |
| (vi) To the sixth portion, KI solution was added, the mixture warmed then cooled. | Yellow precipitate which disappears on warning but re – appears on cooling was observed. | Pb2+ confirmed |
Conclusion
(a) (i) Cation present in Y was 𝐏𝐛𝟐+
- Anion present in Y was 𝐍𝐎𝟑−
- The chemical formula for Y was 𝐏𝐛(𝐍𝐎𝟑)𝟐
(iv) Compound Y was Lead (II) nitrate
(v) Reactions that took place at experiments (b) and (c) (ii) are;-
- Reaction at experiment (b)
Heat
2Pb(NO3)2(s) → 2PbO(s) + 4NO2(g) + O2(g)
- Reaction at experiment (c) (ii)
2Pb(NO3)2(s) + H2SO4(l) → PbSO4(s) + 2HNO3(aq)
(b) Two chemical properties of the sample Yare;-
- It decomposes to give oxide (PbO) and gases (NO2 and O2) ➢ It is soluble in water.
- It react with sulphuric acid to give lead (II) sulphate and nitric acid
2Pb(NO3)2(s) + H2SO4(l) → PbSO4(s) + 2HNO3(aq)
- Uses of a metal present in the sample Y.
❖ Metal present in sample Y is Lead and the following are the uses of Lead metal.
- Used in production of lead – acidic batteries.
- Used as a radiation shield in hospitals, nuclear power plants and other facilities.
- Used in production of alloys.
- Used in production of pigments such as lead chromate and lead oxide.
- Used in the production of certain ceramics such as glazes for pottery and tiles.
- Uses of the sample Y [Lead (II) nitrate] are;-
- Lead (II) nitrate is used in the production of coloured dyes and pigments
- Used in manufacturing of lead – acid based batteries
- Used in the production of heat stabilizers for plastics
- Used as an analytical reagent in chemical laboratories
- Used in preparation of other lead compounds
- Used in the production of catalyst for chemical reactions
- Used in production of fireworks and explosives
- Used in preservation of wood and leather
- Used in mining industries for flotation reagents
ALTERNATIVE SOLUTION FOR THIS KIND OF QUESTIONS
Experimental table
| S/N | Observation | Inference |
| (a) | (i) Colour
• White colour was observed
|
NH4+, Na+, Ca2+, Zn2+, Pb2+ may be present Or Transition metals Fe2+, Fe3+, Cu2+ may be absent |
|
(ii) Texture • Crystalline form was observed. |
NO−3 , SO24−, Cl− may be present
|
|
|
(b) |
Reddish brown fumes evolved which turn moist blue litmus paper red and a gas which rekindles a glowing wooden splint was observed.
|
NO−3 may be present
|
| Cracking sound with brown gas was observed. | NO−3 of Pb2+ may be present
|
|
|
Residue reddish brown when hot and yellow when cold was observed.
|
Pb2+ may be present
|
|
| (c)
|
(i)
• No gas evolved |
SO24−, NO−3 , Cl− may be present |
|
• White precipitate was observed
|
Pb2+ may be present
|
|
|
(ii) Brown fumes evolved which turn moist blue litmus paper red and intensify on addition of copper turnings.
|
NO−3 may be present |
|
|
(iii) White precipitate was formed soluble in excess.
|
Zn2+, Pb2+ may be present
|
|
|
(iv) White precipitate was formed insoluble in excess.
|
Pb2+ may be present
|
|
|
(v) Brown ring was formed at the junction of the liquids.
|
NO−3 confirmed |
|
|
(vi) Yellow precipitate which disappears on warning but re – appears on cooling was observed.
|
Pb2+ confirmed |
UNGUIDED QUALITATIVE ANALYSIS
- Sample P contains one cation and one anion. Using systematic qualitative analysis procedures. Record carefully your experiments, observations, inferences and finally identify the anion and cation in sample P.
Table
| S/N | Experiment | Observation | Inference |
Conclusion
- (i) The cation present in sample P is ___________.
(ii) The anion present in sample P is ___________.
- The chemical formula of sample P is _________.
- The chemical name of sample P is _________.
- Write a balanced chemical equation when the sample solution reacts with any dilute strong acid
Assuming the following materials, chemicals and reagents were given in 3 hours instructions. ✓ Sample labeled P (FeSO4)
- Source of heat e.g Bunsen burner producing non – luminous flame
- Blue litmus paper
- HCl
- Distilled water
- NaOH solution
- Potassium hexacyanoferrate (II) solution
- Barium chloride
- Laboratory apparatuses for qualitative analysis experiments
- Qualitative analysis guide sheet SOLUTION
Experimental table
| S/N | Experiment | Observation | Inference |
| 1. | Appearance of solid sample P.
(i) Colour |
Pale green (light green) colour was observed.
|
Fe2+ may be present
|
|
(ii) Texture |
Crystalline form was observed | NO−3 , SO24−, Cl− may be present
|
|
| 2. | Flame test on a solid sample P.
• Back side of the test – tube was dipped in concentrated HCl then heated it on a non – luminous flame.
|
Yellow (orange) sparks was observed |
Fe2+, Fe3+ may be present
|
| 3. | Action of heat on a solid sample P.
• A small amount (about 0.5 g) of the solid sample P was transferred in a dry test – tube. Heated gently and strongly until no further change. The gas evolved was tested and the appearance of the residues was observed. |
Colourless gas with pungent smell evolved, which turns moist blue litmus paper red.
|
SO24− may be present
|
| Reddish – brown residue was observed
|
Fe2+, Fe3+ may be
present
|
||
| 4. | Action of Dilute 𝐇𝐂𝐥 on a solid sample P.
• A small amount of solid sample P was transferred in a test – tube followed by three (3) drops of dilute HCl
|
No gas evolved |
SO24−, NO−3 , Cl− may be present
|
| 5. | Solubility of solid sample P.
• A small amount of the solid sample P was transferred into the test – tube then enough cold distilled water was added to dissolve the solid sample P.
|
Soluble forming pale green solution |
Fe2+ may be present |
| 6. | Action of 𝐍𝐚𝐎𝐇 solution on a sample solution P.
• To a small volume of (about 1cm3 of the original sample solution, sodium hydroxide solution was added drop – wise until in excess.
|
Green precipitate was formed, insoluble in excess which turns brown on standing |
Fe2+ may be present |
| 7. | Confirmatory tests for 𝐅𝐞𝟐+, 𝐅𝐞𝟑+
• To a small volume of the sample solution, few drops of potassium hexacyanoferrate (III) solution was added
|
Deep blue precipitate was observed. |
Fe2+ confirmed |
| 8. | Confirmatory tests for 𝐒𝐎𝟐𝟒−
• A small volume of the original sample solution was transferred into the test – tube, then barium chloride solution was added followed by dilute HCl
|
White precipitate insoluble in dilute HCl was observed |
SO24− confirmed |
Conclusion
- (i) The cation present in sample P was 𝐅𝐞𝟐+
- The anion present in sample P was 𝐒𝐎𝟐𝟒−
- The chemical formula of sample P is 𝐅𝐞𝐒𝐎𝟒
(vii) The chemical name of sample P is Iron (II) sulphate
- A balanced chemical equation when the sample solution reacts with any dilute strong acid
- FeSO4(s) + 2HCl(aq) → FeCl2(aq) + H2SO4(aq)
