Answer to Question #129440 in General Chemistry for A

Question

Hi,

The liberation of a pungent gas, which turns red litmus paper blue, upon the addition of concentrated sodium hydroxide and aluminum is a positive result for which anion?Please choose:
Phosphate
Nitrate
Sulfite
Halide
Sulfate
Thiocyanate
Carbonate
Thanks

Answer 1

It is nitrate.The logic is simple: Pungent gas is NH₃ , which turns red litmus paper blue, because it is basic. It is formed by reduction of our unknown anion using aluminum. The only anion out of those presented that can form NH₃ is nitrate. The overall reaction may be presented as: 3NaNO₃ + 21NaOH + 8Al + 18H₂O → 8Na₃(Al(OH)₆) + 3NH₃ (instead of Na can be any alkali metal)