Question

A highly pure dilute solution of sodium in liquid ammonia … A) has a blue colour; B) exhibits electrical conductivity; C) produces sodium amide; D) produces hydrogen gas, Which of the above answers is/are correct?

Answer 1

The answer is A) and B).

Explanation:

A)

In dilute solutions of `"Na"` in ammonia, the solvated electrons have a deep blue colour.

In more concentrated solutions, the solution takes on a bronze/copper colour.

B)

The equation is

`"Na(s)" + (x+y)"NH"_3("l") → "Na"^+("NH"_3)_x + e^(-)("NH"_3)`

The solution exhibits electricity because the solvated ions and electrons can carry the current.

The conductivity obviously depends on the concentration, but concentrated solutions (> 3 mol/L) are better conductors than liquid mercury.

C) and D)

The solution of sodium in liquid ammonia is quite stable on its own.

You need to add a small amount of a catalyst such as `"FeCl"_3` for the sodium to react with the ammonia to form sodium amide and hydrogen gas.

`"2Na(s) + 2NH"_3("l") stackrelcolor (blue)("FeCl"_3color(white)(m))(→) 2"NaNH"_2("NH"_3) +"H"_2(g)`