What mass of NH4ClO4 was placed in the flask?

Question

An unknown mass of ammonium perchlorate (117.5g/mol) is placed in an evacuated 1.00L flask and heated to 251C. At this temp the NH4ClO4 decomposes violently. The gaseous products exert a pressure of 466mm Hg at 251C.

Answer 1

Assuming that the reaction is (though others have been reported depending on the temperature) ...

2NH4ClO4 -->  N2 + Cl2 + 2O2 + 4H2O

Then 2mol NH4ClO4 --> 8 mol of gas (1 mol --> 4 mol)

converting to suitable units and substituting into pV = nRT ...

((466/760) X 101325) X 0.001 = n X 8.3 X 524

Giving n = 0.0143 mol of gas.

So there were 0.0143/4 mol of perchlorate to begin with.

So mass = 0.00357 X 117.5 = 0.42 g (to 2 s.f.)