The method used by Joseph Priestley to obtain oxygen made use of the thermal decomposition of mercuric oxide given below. What volume of oxygen gas, measured at 39°C and 725 torr, can be produced from the complete decomposition of 3.97 g mercuric oxide?

The volume of the oxygen gas is 0.246 L

Explanation:

Step 1: Data given

Temperature = 39 °C = 312 K

Temperature = 725 torr = 725 / 760 atm =  0.953947 atm

Mass of mercuric oxide = 3.97 grams

Molar mass of mercuric oxide = 216.59 g/mol

Step 2: The balanced equation

2HgO → 2Hg + O2

Step 3: Calculate moles mercuric oxide

Moles = mass / molar mass

Moles HgO = 3.97 grams / 216.59 g/mol

Moles HgO = 0.0183 moles

Step 3: Calculate moles oxyen

For 2 moles HgO we'll have 2 moles Hg and 1 mol O2

For 0.0183 moles HgO we'll have 0.0183/2 = 0.00915 moles O2

Step 4: Calculate volume O2

p*V = n*R*T

⇒with p = the pressure of the gas = 0.953947 atm

⇒with V = the volume of O2 gas = TO BE DETERMINED

⇒with n = the moles of O2 = 0.00915 moles

⇒with R = the gas constant = 0.08206 L*atm/mol*K

⇒with T = the temperature = 312 K

V = (n*R*T)/p

V = (0.00915 moles * 0.08206 L*atm/mol*K * 312 K ) / 0.953947 atm

V = 0.246 L

The volume of the oxygen gas is 0.246 L

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