How to write a report in qualitative analysis questions

GUIDED QUALITATIVE ANALYSIS

1. 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 𝐏𝐛^𝟐+

• Anion present in Y was 𝐍𝐎_𝟑⁻
• The chemical formula for Y was 𝐏𝐛(𝐍𝐎_𝟑)_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) + 4NO_2(g) + O_2(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

1. 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 𝐅𝐞^𝟐+
• The anion present in sample P was 𝐒𝐎^𝟐_𝟒⁻
• The chemical formula of sample P is 𝐅𝐞𝐒𝐎_𝟒

(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
• FeSO_4(s) +  2HCl_(aq)                →     FeCl_2(aq)  + H₂SO_4(aq)