The effect of pH on the solubility of Al(OH)3 is shown in figure.Other examples of amphoteric hydroxides include Zn(OH)2,Cr(OH)2,Sn(OH)2 andPb(OH)2, which react with excess OH- ions to from the soluble complexions Zn(OH)42-(zincate ion), Cr(OH)4¯ (chromite ion), Sn(OH)3¯(stannite ion), and Pb(OH3)¯ (plumbite ion),respectively.By contrast, basic hydroxides, such as Mn(OH)2,Fe(OH)2,and Fe(OH)3, dissolve in strong acid but not in strong base.Aluminium is mined as bauxite (Al2O3.xH2O) a hydrated oxide that is always contaminated with Fe2O3 and SiO2. Dissolution of Al(OH)3 in excess base is just a special case of the effect of complex-ion formation on solubility.Al(OH)3 dissolves because excess OH-ions convert it to the soluble complex ion(aluminate ion). Can you explain this answer?Īmphoteric oxides,such as aluminium oxide, are soluble both in strongly acidic and in strongly basic solutions. c)First treat bauxite with a strong acid solution (like HCl) and filter it, then treat the remaining filterate with NaOH solution and heat the precipitate obtained.d)First treat bauxite solution with a strong alkali like NaOH and filter it, then to filtrate add a strong acid like HCl and heat the precipitate obtained.Correct answer is option 'B'. In Bayer process, Al2O3 is purified by some reagents, which of the following reagents will be the best for this purification (Note : Strong heating of precipitate of Al(OH)3 produces Al2O3)a)First treat bauxite with a weak acid (like CO2) and then treat the remaining solution with NaOH solution and heat the precipitate obtained.b)First treat the bauxite with strong NaOH solution and filter it, then neutralise the remaining filterate with a weak acid (like CO2) and heat the precipitate obtained. Can you explain this answer? | EduRev JEE QuestionĪmphoteric oxides,such as aluminium oxide, are soluble both in strongly acidic and in strongly basic solutions. Amphoteric oxides,such as aluminium oxide, are soluble both in strongly acidic and in strongly basic solutions.
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