Question

The great French chemist Antoine Lavoisier discovered the Law of Conservation of Mass in part by doing a famous experiment in 1775. In this experiment Lavoisier found that mercury(II) oxide, when heated, decomposed into liquid mercury and an invisible and previously unknown substance: oxygen gas.

Answer 1

Complete Question:

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

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2. Suppose 59.0 mL of dioxygen gas are produced by this reaction, at a temperature of 90.0°C and a pressure of exactly 1 atm. Calculate the mass of mercury (II) oxide that must have reacted.

Answer:

1. 2HgO(s) → 2Hg(l) + O₂(g)

2. 0.8664 g

Explanation:

1. The reaction will be:

HgO(s) → Hg(l) + O₂(g)

To balance the equation, all the elements must have the same amount at both sides of the equation, so HgO and Hg must be multiplied by 2:

2HgO(s) → 2Hg(l) + O₂(g)

2. By the ideal gas law, we can find how many moles of O₂ was produced:

PV = nRT

Where P is the pressure (1 atm), V is the volume (59.0 mL = 0.059 L), n is the number of moles, R is the gas constant (0.082 atm.L/mol.K), and T is the temperature (90.0°C = 363 K).

1*0.059 = n*0.082*363

29.766n = 0.059

n = 0.002 mol

By the stoichiometry of the reaction:

2 moles of HgO ------------------ 1 mol of O₂

          x               ------------------ 0.002 mol

By a simple direct three rule:

x = 0.004 mol of HgO

The molecular mass of HgO is 216.59 g/mol. The mass is the number of moles multiplied by the molecular mass:

m = 0.004 * 216.59

m = 0.8664 g