# Quick Stoich & Gasses

I have a quick question in Stoich and Gasses, I however could not get any far, any answer will be appreciated. Thank You.

A sample of $\ce{Pb(NO3)2}$ is heated, yielding $\ce{O2, NO2\ gas,\ and\ solid\ PbO}$. A $\ce{293 \ ml}$ gas sample, measured at $\ce{200C}$ and $\ce{1\ atm}$, is collected. What was the mass of the $\ce{Pb(NO3)2}$ sample?

I feel like in this situation I need to have only one gas so I can apply the Ideal Gas Law to solve and find the mass of $\ce{Pb(NO3)2}$. What should I do there are two gasses and I don't know the volumes or the masses?

$$\ce{2Pb(NO3)2 -> O2 + 4NO2 + 4PbO}$$

• You can still assume ideal gas conditions even if it's a mixture of several gasses. You also need a reaction equation. – tschoppi Dec 8 '14 at 23:31
• @tschoppi I don't quite grasp that. – Asker123 Dec 9 '14 at 0:28
• You don't need a molar mass. If you're looking for one, you're completely on the wrong track. – tschoppi Dec 9 '14 at 0:29

You assume ideal gas, which means that the gas particles are indistinguishable. This means the reaction equation could look like $$\ce{2Pb(NO3)2 -> 5X + 4PbO}$$ where 5 moles of gas are liberated for every 2 moles of lead nitrate.
Reforming the ideal gas equation to $n=pV/(RT)$ will lead you to the numerical value. The amount of lead nitrate will then be $$n_{\ce{Pb(NO3)2}} = \frac{2n}{5}$$