Solving for a gaseous reactant

Question

Write a balanced chemical equation, including physical state symbols, for the decomposition of solid mercury(II) oxide (HgO) into liquid mercury and gaseous dioxygen.

 

Suppose 86.0 mL of dioxygen gas are produced by this reaction, at a temperature of 90.0 C and pressures of exactly 1 atm. Calculate the mass of mercury(II) oxide that must have reacted. Be sure your answer has the correct number of signifigant digits. 

Answer 1

2HgO(s) → 2Hg(l) + O₂(g)

 

PV = nRT

n = PV/RT

n = 1 atm x .086 L/(0.0821 L atm mol^-1 K^-1 x 363 K)

n = .002885 mol O₂

 

.002885 mol O₂ x 2 mol HgO/1 mol O₂ x 216.59 g HgO/1 mol HgO = 1.249 g HgO

 

In significant digits its 1 g.