Devarda's alloy

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Devarda's alloy is an alloy of aluminium (44%-46%), copper (49%-51%) and zinc (4%-6%). It is a reducing agent.

It can be used as a test for the nitrate anion. When a solution of nitrate ions are mixed with aqueous sodium hydroxide, adding Devarda's alloy and heating the mixture gently, liberates ammonia gas.

The reaction is given by the ionic equation:

3NO₃^- + 8Al + 5OH^- + 18H₂O → 3NH₃(g) + 8[Al(OH)₄]^-

To distinguish between NO₃^- and NO₂^- dilute HCl must be added to the nitrate.The 'Brown Ring Test' can also be used.

[edit] External links

• National Pollutant Inventory - Copper and compounds fact sheet