(2a)
Procedure:
Add all of C into a beaker with 10cm³ of distilled water and stir. Test the resulting solution with both red and blue litmus papers.
Observation:
Blue litmus paper turns red, red litmus paper remains unchanged.
Inference:
The solution is acidic.
(2bi)
First portion: Add NaOH(aq) in drops, then in excess
Observation:
A white gelatinous precipitate forms on addition of NaOH, which dissolves in excess NaOH.
Inference:
Presence of aluminium ions (Al³⁺).
(2bii)
Second portion: Add NH₃(aq) in drops, then in excess
Observation:
A white gelatinous precipitate forms, which is insoluble in excess ammonia.
Inference:
Confirms Al³⁺ ion, since Al(OH)₃ does not dissolve in excess NH₃.
(2biii)
Third portion: Add BaCl₂(aq), followed by dilute HCl
Observation:
A white precipitate forms with BaCl₂, which is insoluble in dilute HCl.
Inference:
Indicates the presence of sulfate ions (SO₄²⁻).
(2biv)
Fourth portion: Add Fehling’s solution A and B and boil.
Observation:
No red precipitate forms.
Inference:
No reducing sugar present.
Conclusion:
From all tests, the two substances present in mixture C are:
(i) Aluminium salt (e.g. aluminium sulfate Al₂(SO₄)3) gives Al³⁺ and SO₄²⁻
(ii) No reducing sugar or organic acid detected
Number 3
(3a)
Ammonia (NH₃)
(3b)
White smoke with HCl
(3c)
(NH₄)₂SO₄
(3d)
Ammonium sulfate
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COMPLETED!!!
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