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CGP EDU Academic Team
Published on: August 13, 2026
Why use of excess cobalt nitrate solution should be avoided in the dry test of aluminium compounds ?
Text Solution
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2Al 2 O 3 +2Co 2+ + 
2CoAl 2 O 4 (thenard blue) +4NO 2 + O 2
In case of excess of Co(NO 3 ) 2 , CoAl 2 O 3 will produce black cobalt oxide (CO 3 O 4 ), which will mask the blue colour.
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