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Sodium azide is used in automobile air bags as a source of nitrogen gas. The common...

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  1. Sodium azide is used in automobile air bags as a source of nitrogen gas. The common synthesis method of the sodium azide proceeds in two steps from ammonia. In the first step, ammonia is converted to sodium amide, which is subsequently combined with dinitrogen monoxide to yield the title compound according to the equations shown below:


2 Na (s) + 2 NH3 (g) à 2 NaNH2 (s) + H2 (g)

2NaNH2 (s) + N2O (g) à NaN3 (s) + NH3 (g)


  1.  If 0.710 g of sodium is mixed with 1.00 g of ammonia, what mass, in grams, of sodium amide is formed?

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The second reaction also produces NaOH, alongside other products shown in the equation.

The balanced chemical reactions are:

             2 Na (s) + 2 NH3 (g) = 2 NaNH2 (s) + H2 (g) ------ (i)

Moles:  2                    2                      2              1

Mass (g): 2×23         2×17                2×39

Actually (g): 0.710      1.0

Mole ratio of the two reactants is 1:1. Thus, when 0.710 g = 0.71/23 = 0.03087 moles of sodium is mixed with 1.00 g = 1/17 = 0.0588 moles of ammonia, sodium becomes the limiting reagent. Hence, amount of NaNH2 formed will be dependent upon the mass of reacting sodium, and the other reagent, ammonia will remain somewhat in excess. The stoichiometry of this reaction shows that:

 2×23 g ammonia reacts to produce 2×39 g NaNH2.

0.710 g ammonia should produce 2×39×0.710/(2×23) = 1.204 g NaNH2.

On similar lines, amount of NaN3 formed can easily be calculated from the equation:

2NaNH2 (s) + N2O (g) = NaN3 (s) + NaOH + NH3 (g) ------ (ii)


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