Which one of the following metal oxides does not usually react with sodium hydroxide?
Copper oxide
Aluminium oxide
Potassium oxide
Calcium oxide
Answer is Right!
Answer is Wrong!
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UPSC CAPF – 2021
Aluminium oxide (Al₂O₃) is an amphoteric oxide and reacts with sodium hydroxide: Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O (at high temperature/concentration) or Al₂O₃ + 6NaOH + 3H₂O → 2Na₃[Al(OH)₆] (in aqueous solution).
Potassium oxide (K₂O) and Calcium oxide (CaO) are basic oxides. They react vigorously with water to form potassium hydroxide (KOH) and calcium hydroxide (Ca(OH)₂), respectively, which are strong bases. Being bases, KOH and Ca(OH)₂ do not react with another base like NaOH.
Copper oxide (CuO) is also a basic oxide. It does not react with water and does not react with sodium hydroxide solution under usual conditions.
Among the given options, Aluminium oxide reacts with NaOH. Potassium oxide and Calcium oxide react with water to form hydroxides that do not react with NaOH. Copper oxide is a basic oxide that neither reacts significantly with water nor with NaOH solution under usual conditions. Therefore, Copper oxide is the one that does not usually react with sodium hydroxide.