Question

$Be$ and $ Al $ exhibit diagonal relationship. Which of the following statements about them is/are not true?
I. Both react with $ HCl $ to liberate $ {{H}_{2}} $
II. They are made passive by $ HN{{O}_{3}} $
III. Their carbides give acetylene on treatment with water
IV. Their oxides are amphoteric

• A. III and IV
• B. I and III
• C. I only
• D. II and III
• E. III only

Answer 1

Answer: (E)

(i) $ Be $ and $ Al $ both react with $ HCl $ to liberate $ {{H}_{2}} $ . $ Be+2HCl\xrightarrow[{}]{{}}BeC{{l}_{2}}+{{H}_{2}}\uparrow $ $ 2Al+6HCl\xrightarrow[{}]{{}}2AlC{{l}_{3}}+3{{H}_{2}}\uparrow $
(ii) Be renders passive with cone. $ HN{{O}_{3}} $ and so does not react. Cone. $ HN{{O}_{3}} $ is strong oxidizing agent and forms very thin layer of oxide on the surface of metal. Similarly, $ Al $ become passive in cone. $ HN{{O}_{3}} $ due to formation of oxide layer on the surface.
(iii) Their carbides gives methane on treatment with water.
$ B{{e}_{2}}C+4{{H}_{2}}O\xrightarrow[{}]{{}}2Be{{(OH)}_{2}}+C{{H}_{4}} $
$ A{{l}_{4}}{{C}_{3}}+12{{H}_{2}}O\xrightarrow[{}]{{}}4Al{{(OH)}_{3}}+3C{{H}_{4}} $
(iv) Their oxides, $ BeO $ and $ A{{l}_{2}}{{O}_{3}} $ are amphoteric.