Experimentally Determining The Moles & Molar Mass of Hydrogen Applying Avogadro’s Law Using the Ideal Gas Law & Partial Pressures Dr. Ron Rusay Mg(s) + 2HCl(aq)  MgCl 2 (aq) + H 2 (g) Zn(s) + 2HCl(aq)  ZnCl 2 (aq) + H 2 (g)

What is wrong with this set up? Mg or Zn

Mg(s) + 2HCl(aq)  MgCl 2 (aq) + H 2 (g) Zn(s) + 2HCl(aq)  ZnCl 2 (aq) + H 2 (g)

Ideal Gas Law PV = n RT R = “proportionality” constant = L atm   mol  P = pressure in atm V = volume in liters n = moles T = temperature in Kelvins

Standard Conditions Temperature, Pressure & Moles “STP” For 1 mole of a gas at STP: P = 1 atmosphere T =  C ( K) The molar volume of an ideal gas is liters at STP

P 1 V 1 = P 2 V 2 V 1 / n 1 = V 2 / n 2 V 1 / T 1 = V 2 / T 2 Isobaric process: pressure constant Isochoric process: volume constant Isothermal process: temperature constant

Hydrogen & the Ideal Gas Law n H 2 (g) = PV / RT n = moles H 2 (g) P H 2 (g) = pressure of H 2 (g) in atm (mm Hg  atm) V = experimental volume (mL  L) T = experimental temperature ( o C  K) Mg(s) + 2HCl(aq)  MgCl 2 (aq) + H 2 (g) Zn(s) + 2HCl(aq)  ZnCl 2 (aq) + H 2 (g)

Total Pressure: Sum of the Partial Pressures For a mixture of gases, the total pressure is the sum of the pressures of each gas in the mixture. P Total = P 1 + P 2 + P P Total  n Total n Total = n 1 + n 2 + n 3 +. n Total = n 1 + n 2 + n 3 +.

P H 2 (g) = P Total ( barometric) - P H 2 O (g) [TABLE] - P HCl (g) P HCl (g) = HCl Height (mm) ÷ ___________ Density Hg is times > density HCl(aq) P HCl (g) = HCl Height (mm) x ___________ Density Hg is times > density HCl(aq) mm Hg/cm of acid solution

Ideal Gas Law: Moles & Avogadro’s Law n H 2 (g) = PV / RT n = moles H 2 (g) P H 2 (g) = pressure of H 2 (g) in atm (mm Hg  atm) P H 2 (g) = P Total ( barometric) - P H 2 O (g) [TABLE] - P HCl (g) V = experimental volume (mL  L) T = experimental temperature ( o C  K) Mg(s) + 2HCl(aq)  MgCl 2 (aq) + H 2 (g) Zn(s) + 2HCl(aq)  ZnCl 2 (aq) + H 2 (g)

Ideal Gas Law Simulator

Molar Mass of a Gas (Hydrogen) PV = n RT n = g of gas/ MM gas [MM gas = g/mol] PV = (g of gas/ MM gas )RT MM gas = g of gas/V (RT/P) Density of gas [separate experiment] MM gas = g of gas/V (RT/P) MM gas = density of gas (RT/P)

QUESTION Freon-12, CF 2 Cl 2, a “safe” compressible gas, was widely used from as a refrigerant in refrigerators, freezers, and air conditioning systems. However, it had been shown to be a greenhouse gas and to catalytically destroy the ozone layer. It was phased out and banned. 200 ml of Freon-12 was collected by syringe. It weighed grams, had a temperature of 30.0°C, and a pressure of 730 mm of Hg. What is the experimental molar mass of Freon-12? A.12.0 g/mol B.84 g/mol C.92.7 g/mol D.115 g/mol E.120. g/mol