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ICSE Class 10 Chemistry Question 8 of 18

Solved 2020 Question Paper ICSE Class 10 Chemistry — Question 4

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Question

Question 3(a)

Baeyer's process is used to concentrate bauxite ore to alumina.

Give balanced chemical equations for the reaction taking place for its conversion from bauxite to alumina.

Answer

Conversion of impure bauxite to sodium aluminate:

Al2O3.2H2O [Impure bauxite]Amphoteric oxide+2NaOH [conc. soln]Base→150−200°C2NaAlO2[sodium aluminate]Salt+3H2OWater\underset{\text{Amphoteric oxide}}{\underset{\text{[Impure bauxite]}}{\text{Al}_2\text{O}_3.2\text{H}_2\text{O }}} + \underset{\text{Base}}{\underset{\text{[conc. soln]}}{2\text{NaOH }}} \xrightarrow{150 - 200 \degree\text{C}} \underset{\text{Salt}}{\underset{\text{[sodium aluminate]}}{2\text{NaAlO}_2}} + \underset{\text{Water}}{ \text{3H}_2\text{O}}

Conversion of sodium aluminate to aluminium hydroxide:

NaAlO2[sodium aluminate]+2H2O→50−60°CNaOH[sodium hydroxide]+Al(OH)3[aluminium hydroxide]\underset{\text{[sodium aluminate]}}{\text{NaAlO}_2} + 2\text{H}_2\text{O} \xrightarrow{50 - 60 \degree\text{C}} \underset{\text{[sodium hydroxide]}}{\text{NaOH}} + \underset{\text{[aluminium hydroxide]}}{\text{Al(OH)}_3}

Conversion of Al(OH)3 - to pure alumina - heat on Al(OH)3:

2Al(OH)3[aluminium hydroxide]→1100°CAl2O3[pure alumina]+3H2O\underset{\text{[aluminium hydroxide]}}{\text{2Al(OH)}_3} \xrightarrow{1100\degree\text{C}} \underset{\text{[pure alumina]}}{\text{Al}_2\text{O}_3} + \text{3H}_2\text{O}

Precipitated Al(OH)3 is ignited to give pure alumina [Al2O3]