Q4 / 160 · AP EAMCET 2005 · Chemistry

Observe the following statements regarding purification of bauxite I. During Hall's process, silica is removed as Si (vapour). II. Bauxite ore contaminated with $\mathrm{Fe}_2 \mathrm{O}_3$ is purified in Baeyer's process. III. During Serpeck's process, AlN is formed. The correct answer is

  • A
    I, II and III are correct
  • B
    Only I and II are correct
  • C
    Only I and III are correct
  • Correct answer
    D
    Only II and III are correct

Solution

Red bauxite which contains $\mathrm{Fe}_2 \mathrm{O}_3$ as the main impurity, is refined either by Baeyer's process or by Hall's process. White bauxite containing $\mathrm{SiO}_2$ impurity is refined by Serpeck's method. In Serpeck's method, following reactions take place. $\begin{gathered} \mathrm{Al}_2 \mathrm{O}_3 \cdot 2 \mathrm{H}_2 \mathrm{O}+3 \mathrm{C}+\mathrm{N}_2 \stackrel{1800^{\circ} \mathrm{C}}{\longrightarrow} 2 \mathrm{AlN}+3 \mathrm{CO}+2 \mathrm{H}_2 \mathrm{O} \\ \mathrm{AlN}+3 \mathrm{H}_2 \mathrm{O} \longrightarrow \mathrm{Al}(\mathrm{OH})_3+\mathrm{NH}_3 \\ 2 \mathrm{Al}(\mathrm{OH})_3 \longrightarrow \mathrm{Al}_2 \mathrm{O}_3+3 \mathrm{H}_2 \mathrm{O} \end{gathered}$

Hence, the correct answer is option: 'D'.

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