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Question
Highly pure dilute solution of sodium in liquid ammonia :
Highly pure dilute solution of sodium in liquid ammonia :
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Solution
The correct options are
A Shows blue colour
B exhibits electrical conductivity
C produce hydrogen gas on standing
Blue colour is due to the presence of solvated (ammoniated) electrons.
M→M++e− M++xNH3→[M(NH3)x]+ e−+yNH3→[e(NH3)y]−On adding ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯M+(x+y)NH3→[M(NH3)x]++[e(NH3)y]− Ammoniated carbon Ammoniated electron
Note : Sodium in liquid ammonia forms NaNH2 only in presence of a catalyst like Pt black, iron oxide etc.
[e(NH3)y]−Fe2O3⟶NH−2+(y−1)NH3
On standing, it slowly liberates hydrogen resulting in the formation of amide.
M+(am)+e−+NH3(l)→MNH2(am)+12H2(g)
where ‘am’ denotes solution in ammonia.
The electrical conductivity of the solution is due to both ammoniated cations and ammoniated electrons.
THEORY
General Characteristics:
Halides of alkali metals:
Other halides of lithium such as LiCl, LiBr, LiI, LiF are soluble in ethanol, acetone, and ethyl acetate. LiCl is soluble in pyridine too.
Solutions in liquid ammonia:
The alkali metals dissolve in liquid ammonia giving a deep blue solution that is conducting in nature.
M+(x+y)NH3→[M(NH3)x]++[e(NH3)y]−
The solution is paramagnetic due to the presence of free or ammoniated electrons i.e [e(NH3)y]−
The ammoniated electrons in the solution absorb energy in the visible region of light, Imparting blue color to the solution.
In a Concentrated solution (above 3 M), blue color changes to copper-bronze/bronze color with a metallic lustre.
Due to the formation of metal ion clusters, it becomes diamagnetic.
Ammoniated electrons with opposite electron spin associate to form diamagnetic electron pairs.
ms=+12, ms=−12
The conductivity of deep blue solutions is similar to that of pure metals.
Due to the presence of solvated electrons (also due to solvated cations), the conductivity decreases as the concentration increases.
Evaporation of the ammonia from the blue solutions of alkali metals yields the metal.
The blue solutions are moderately stable at room temperature, where ammonia is still a liquid.
But the reaction to give amide can occur photochemically and is catalyzed by transition metals (like Fe) and impurities.
On standing, it slowly liberates hydrogen resulting in the formation of amide.
M+am+e−+NH3(l)→MNH2(am)+12H2(g)
where ‘am’ denotes solution in ammonia.
A Shows blue colour
B exhibits electrical conductivity
C produce hydrogen gas on standing
Blue colour is due to the presence of solvated (ammoniated) electrons.
M→M++e− M++xNH3→[M(NH3)x]+ e−+yNH3→[e(NH3)y]−On adding ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯M+(x+y)NH3→[M(NH3)x]++[e(NH3)y]− Ammoniated carbon Ammoniated electron
Note : Sodium in liquid ammonia forms NaNH2 only in presence of a catalyst like Pt black, iron oxide etc.
[e(NH3)y]−Fe2O3⟶NH−2+(y−1)NH3
On standing, it slowly liberates hydrogen resulting in the formation of amide.
M+(am)+e−+NH3(l)→MNH2(am)+12H2(g)
where ‘am’ denotes solution in ammonia.
The electrical conductivity of the solution is due to both ammoniated cations and ammoniated electrons.
THEORY
General Characteristics:
Halides of alkali metals:
Other halides of lithium such as LiCl, LiBr, LiI, LiF are soluble in ethanol, acetone, and ethyl acetate. LiCl is soluble in pyridine too.
Solutions in liquid ammonia:
The alkali metals dissolve in liquid ammonia giving a deep blue solution that is conducting in nature.
M+(x+y)NH3→[M(NH3)x]++[e(NH3)y]−
The solution is paramagnetic due to the presence of free or ammoniated electrons i.e [e(NH3)y]−
The ammoniated electrons in the solution absorb energy in the visible region of light, Imparting blue color to the solution.
In a Concentrated solution (above 3 M), blue color changes to copper-bronze/bronze color with a metallic lustre.
Due to the formation of metal ion clusters, it becomes diamagnetic.
Ammoniated electrons with opposite electron spin associate to form diamagnetic electron pairs.
ms=+12, ms=−12
The conductivity of deep blue solutions is similar to that of pure metals.
Due to the presence of solvated electrons (also due to solvated cations), the conductivity decreases as the concentration increases.
Evaporation of the ammonia from the blue solutions of alkali metals yields the metal.
The blue solutions are moderately stable at room temperature, where ammonia is still a liquid.
But the reaction to give amide can occur photochemically and is catalyzed by transition metals (like Fe) and impurities.
On standing, it slowly liberates hydrogen resulting in the formation of amide.
M+am+e−+NH3(l)→MNH2(am)+12H2(g)
where ‘am’ denotes solution in ammonia.
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