Question

What is the mass of mercuric oxide (216.59 g/mol) that decomposes to release 0.750L of oxygen gas at STP?

​HgO(s) Hg(l) + O2(g)

Answer 1

At STP,

p = 1 atm

T = 273 K

R = 0.0821 L.atm/K.mol

V = 0.750 L

n = ?

Ideal gas equation,

p V = n R T

1 X 0.750 = n X 0.0821 X 273

0.750 = n X 22.4

n = 0.750 / 22.4

n = 0.0335 mol

The given balanced equation is,

2 HgO (s) --------------> 2 Hg (l) + O2 (g)

From the balanced equation,

1 mol of O2 is produced from 2 mol of HgO

Then,

0.0335 mol of O2 is produced from 2 X 0.0335 = 0.0670 mol of HgO

Moles of HgO required = 0.0670 mol

Molar mass of HgO = 216.59 g/mol

Mass of HgO = Moles X molar mass

= 0.0670 X 216.59

= 14.5 g.

Therefore,

Mass of mercuric oxide decomposed = 14.5 g.