Question

A 3.31 g sample of lead nitrate, Pb(NO 3 ) 2 , molar mass = 331 g/mol, is heated in an evacuated cylinder with a volume of 1.62 L. The salt decomposes when heated according to the equation: . Assuming complete decomposition, what is the pressure in the cylinder after decomposition and cooling to a temperature of 300 K? Assume the PbO takes up negligible volume.

Answer 1

Answer:

$P=0.152\ atm$

Explanation:

Given:

• The volume of the cylinder, $V=1.62\ L$

• The mass of the sample, $m=3.31\ g$

• The temperature, $T=300\ K$

• The molar mass of lead nitrate is $M=331\ g/mol$

Now, no. of moles:

$n=\frac{m}{M}$

where:

m = mass in gram

M = molecular mass

$n=\frac{3.31}{331}$

$n=0.01\ mol$

From the ideal gas law:

$P.V=n.R.T$

$P\times 1.62=0.01\times 0.08206\times300$

$P=0.152\ atm$