Built by Aabis
Notebook Theme

Analysis of Lead Acetate (Pb(CH₃COO)₂)

Class 12 Chemistry Practical

How to do salt analysis · Viva · Quiz

Aim

To analyse the given inorganic salt for one acidic and one basic radical.

Preliminary Test

ExperimentObservationInference
Physical examinationWhite crystalline solid; vinegar-like smellAcetate may be present
SolubilitySoluble in waterWater-soluble lead salt (not the chloride/sulphate)
Dry heatingMay crackle; vapours smell of vinegar; residue often yellow (PbO)Lead acetate indicated
Flame testNo alkali-earth flame; sometimes a pale bluish-white tingeNot Ba / Sr / Ca
Dilute H₂SO₄Vinegar-like vapours of acetic acidCH₃COO⁻ may be present
Conc. H₂SO₄Vinegar vapours; no chromyl / halide fumes of Cl₂, Br₂, I₂Acetate, not a halide

Test of Anion (CH₃COO⁻)

ExperimentObservationInference
Warm the salt with dilute H₂SO₄Vapours with a vinegar-like smellCH₃COO⁻ may be present
Confirmatory Tests
Ester test
Heat salt + ethanol + a few drops of conc. H₂SO₄. Pour into water and smell		Fruity odour of ethyl acetateCH₃COO⁻ is confirmed
Ferric chloride
Add neutral FeCl₃ to the aqueous solution		Deep red colour; on boiling, a reddish-brown ppt of basic ferric acetateCH₃COO⁻ is confirmed

Ionic equations

  • 2CH₃COO⁻ + 2H⁺ → 2CH₃COOH (vinegar smell)
  • CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O (ester)
  • 3CH₃COO⁻ + Fe³⁺ → (CH₃COO)₃Fe (deep red)

Test of Cation (Pb²⁺)

ExperimentObservationInference
To the original solution add dilute HClWhite ppt of PbCl₂, soluble in hot water, reappears on coolingGroup I (Pb²⁺) may be present
Confirmatory Tests
Potassium iodide
To the hot solution of the ppt add KI		Yellow ppt of PbI₂ (golden spangles on cooling)Pb²⁺ is confirmed
Potassium chromate
To the acidified solution add K₂CrO₄		Yellow ppt of PbCrO₄, insoluble in acetic acidPb²⁺ is confirmed

Ionic equations

  • Pb²⁺ + 2Cl⁻ → PbCl₂ ↓
  • Pb²⁺ + 2I⁻ → PbI₂ ↓ (yellow)
  • Pb²⁺ + CrO₄²⁻ → PbCrO₄ ↓ (yellow)

Result

The given salt contains Pb²⁺ as the cation (basic radical) and CH₃COO⁻ as the anion (acidic radical). The salt is Lead Acetate (Pb(CH₃COO)₂).

Precautions

  1. Use small quantities of salt and reagents; do not use excess.
  2. Keep the mouth of the test tube away from the face while heating.
  3. Use freshly prepared FeSO₄ for the brown ring test.
  4. Nessler’s reagent is toxic (mercury); handle with care and do not pipette by mouth.

Viva voce

  1. Why is lead placed in Group I?

    PbCl₂ is insoluble in cold dilute HCl.

  2. Why is the ppt dissolved in hot water?

    PbCl₂ dissolves in hot water. AgCl does not. That is how you separate lead from silver.

  3. What are golden spangles?

    Shining yellow crystals of PbI₂ that appear on cooling the hot solution.

  4. Why vinegar smell with dilute acid?

    Acetate + H⁺ → acetic acid, which is volatile and smells of vinegar.

  5. Why is the ester test done with conc. H₂SO₄?

    Conc. H₂SO₄ is a dehydrating catalyst for esterification.

  6. Why must FeCl₃ be neutral?

    Free acid prevents formation of the deep-red ferric acetate complex.

  7. Why yellow ppt with K₂CrO₄?

    PbCrO₄ is an insoluble yellow chromate used also as a pigment (chrome yellow).

  8. Why not pass H₂S in acid for this salt after Group I is positive?

    Once Pb²⁺ is confirmed, later groups are not run.

Related salts

लेड एसीटेट (हिन्दी में)

नमक: लेड एसीटेट। अम्लीय मूलक: एसीटेट (सिरके जैसी गंध)। क्षारीय मूलक: लेड, वर्ग I।

तनु HCl से सफेद PbCl₂, गर्म जल में घुल जाता है। KI से पीला PbI₂ (सुनहरे स्पैंगल्स)।

एसीटेट की पुष्टि एस्टर परीक्षण (फल जैसी गंध) और उदासीन FeCl₃ से गहरे लाल रंग से होती है।