Some airbags in cars contain a mixture of sodium azide (NaN3), sodium nitrate (N

Question

Some airbags in cars contain a mixture of sodium azide (NaN3), sodium nitrate (NaNO or potassium nitrate in some cases) and silicone dioxide (SiO2). When the car undergoes a collision, a series of three chemical reactions produce N2 gas to fill the airbag and convert highly toxic NaN3 (The maximum concentration of NaNg allowed in the workplace is 0.2 mg/m3 air), to harmless glass. Even sodium oxide (Na2O) is toxic. The reactions are 2NaNjà 2Na+ 3N2 10Na +2NaNO3 à N2 +6Na2O Na2O + 10 SiO2 à glass NaN3 can decompose at 300°C to produce sodium metal (Na) and nitrogen gas (N2). In one preparation, 150 g of NaNg are used in an airbag. If all of the sodium in the system can be safely sequestered as glass then grams of NaNO3 and SiO2 must be included are gm and gm 0.462 and 13.85 O 39.3 and 831 O 39.3 and 83.1 O 0.462 and 39.3

Explanation / Answer

T = 300C = 300+273 = 573 K

NaN3 moles = mass / Molar mass of NaN3 = ( 150g) / ( 65g/mol) = 2.3077

Na moles = NaN3 moles = 2.3077,  

out of 10 Na combines with 2NaNO3 , hence NaNO3 = ( 2/10) ( 2.3077) = 0.46154 mol

NaNO3 mass = moles x molar mass of NaNO3 = 0.46154 mol x 85g/mol = 39.3 g

10 Na gives 6 Na2O , hence Na2O moles = (6/10) ( 2.3077) = 1.3846

1 Na2O gives 10 SiO2 , hence SiO2 moles = 10 x 1.3846 = 13.846 mol

SiO2 mass = moles x molar mass of SiO2 = 13.846 mol x 60 g/mol = 831 g

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