[Rutherford]

Most modern automobiles are equipped with air bags which are very effective in reducing the number of traffic fatalities. During a front-end collision, the air bag sensor sends an electric signal that triggers the rapid decomposition of an unknown compound X which releases a large amount of a certain gas. Within a very short period of time, the air bag inflates to protect the driver and passengers from frontal impact.

A 1.00 g sample of X is decomposed to release 507 mL (110 kPa, 18 C) of gas A, which is one of the components of air. The reaction also yields a solid residue. Treatment of the residue with an excess of water produces 172 mL (S.T.P.) of gas B. Determine X.

Attempt:
X a A + b Y
Y + c H₂O d B + e Z
n_A=0.0231mol
n_B=0.0077mol
I also assumed that d=1, so n_y=n_B therefore the molar ration of A and Y produced by the decomposition of X is 3:1. Here I am stuck. What to do now?

[Rutherford]

I think that there isn't enough data given, but I want someone to confirm it (or disprove).

[Borek]

You either need to know what is put into air bags (and then it takes almost time to confirm the data given), or you need some trial and error. Gas A is most likely either oxygen or nitrogen, and there not that many solids that will react with water producing a gas.

[Rutherford]

How did you guess that it is either oxygen or nitrogen?

For the solids I really don't know. It could be an alkali or earth alkali metal or an hydride of those or some transition metal compound (a transition metal alone won't react with water, right?).

[Borek]

How did you guess that it is either oxygen or nitrogen?

Ar is out of the question (no stable compounds), and other gases are present only in very tiny amounts. Sure, one can argue it can be also carbon dioxide, but I would start with the main ones.

[Rutherford]

I thought about CO and H₂O vapors, too. Again, I don't know the number of moles of each compound produced and what is the solid compound  , so trial and error will only work. Huh, for this problem, one needs more luck than knowledge to solve, as guessing is the only way then .

[AWK]

The only possibility for gas (one component of air) is nitrogen. Oxygen cannot leave an element or compound that evolves other gas with water.
Some problem comes from that solid residue in this case is the element (knowing this or just assuming anyone easily can identify this element).
The other problem is that this is a virtual bag since real bugs contains a mixture of X with KNO₃ to avoid a formation of this element (instead of a less dangerous oxide is formed).

[Borek]

for this problem, one needs more luck than knowledge to solve, as guessing is the only way then

You don't know what is in the air bags? I thought everyone interested in chemistry knows that.

[Rutherford]

I know now, it's never late to find out  . I will check the calculations.

[Rutherford]

By calculation, the solid residue is sodium. And X is sodium-azide.

The only possibility for gas (one component of air) is nitrogen. Oxygen cannot leave an element or compound that evolves other gas with water.

Can this be explained, or it is a common fact?

The other problem is that this is a virtual bag since real bugs contains a mixture of X with KNO₃ to avoid a formation of this element (instead of a less dangerous oxide is formed).

What is the reaction? Is Na₂O formed?

[billnotgatez]

http://en.wikipedia.org/wiki/Airbag#Inflation

is it cheating to look up what was used and start from there

EDIT

I think I can answer my own question

One might have to assume this is a test question and you can not look up stuff.

[Rutherford]

It was on a competition, so the ones that competed couldn't just look up the answer or search on the net while they are solving it.

[AWK]

By calculation, the solid residue is sodium. And X is sodium-azide.

The only possibility for gas (one component of air) is nitrogen. Oxygen cannot leave an element or compound that evolves other gas with water.

Can this be explained, or it is a common fact?

The other problem is that this is a virtual bag since real bugs contains a mixture of X with KNO₃ to avoid a formation of this element (instead of a less dangerous oxide is formed).

What is the reaction? Is Na₂O formed?

Imagine reactive oxygen and vapors of elemental sodium in air bag!.
Na2O + K2O from potassium nitrate.

[Rutherford]

Okay, thanks for the help.