Calculate the mass of sodium amide needed to obtain 550 g of sodium azide, assuming there is a 95.0% yield of sodium azide. Give your answer to 3 significant figures.

2NaNH2 + N2O --> NaN3 + NaOH + NH3

Mr(NaN3) = 65   Mr(NaNH2) = 39    
n(NaN3) = 550/65 = 8.46
100% NaN3 = 550/65 x 100/95 = 8.91
n(NaNH2) = 2 x 8.91 = 17.8
m(NaNH2) = 17.8 x Mr = 17.8 x 39 = 694.7 = 695 g