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Experiment No. N

Analysis of Aluminium Hydroxide (Al(OH)₃)

Aim

To determine the presence of anion and cation in the given salt

Preliminary Test

  • Odor: Odorless
  • Texture: Crystalline
  • Color: White
  • Solubility: Soluble in water

Test of Anion

ExperimentObservationInference
Universal IndicatorSolution turns blue or purpleOH⁻ may be present
Confirmatory Test
Phenolphthalein Test
Add phenolphthalein indicator to salt solution		Solution turns pinkOH⁻ is confirmed

Test of Cation

ExperimentObservationInference
Original solution + Dil. HCl + NH₄Cl solid + NH₄OHWhite gelatinous precipitateAl³⁺ may be present
Confirmatory Tests
Dissolve white precipitate in dilute HCl and divide into two partsTo the first part, add sodium hydroxide and warm. A white gelatinous precipitate dissolves in excess sodium hydroxide solutionAluminium is confirmed
Blue Lake Test
To the second part, add few drops of blue litmus solution and then NH₄OH dropwise along the sides of the test tube		A blue floating mass appears in colourless solutionPresence of Al³⁺ is confirmed

Result

The given salt contains Al³⁺ ions as cation and OH⁻ ions as anion. The salt is Al(OH)₃.

Precautions

  1. Handle the chemicals with care.
  2. Don't use excess of chemicals.
  3. Keep the mouth of the test tube away from the face.