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Determining Moles & Molar Mass of Hydrogen

This video explains the experimental process of determining the moles and molar mass of hydrogen gas using Avogadro's Law and the Ideal Gas Law. It also discusses the setup for the experiment and provides a simulation for further understanding.

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Determining Moles & Molar Mass of Hydrogen

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  1. http://chemconnections.org/general/chem106/Magnesium-Zinc-wo.1.movhttp://chemconnections.org/general/chem106/Magnesium-Zinc-wo.1.mov Experimentally Determining The Moles & Molar Mass of HydrogenApplying Avogadro’s Law Mg(s) + 2HCl(aq)  MgCl2(aq) + H2 (g) Zn(s) + 2HCl(aq)  ZnCl2(aq) + H2 (g) Using the Ideal Gas Law & Partial Pressures Dr. Ron Rusay

  2. What is wrong with this set up? Mg or Zn

  3. Mg(s) + 2HCl(aq)  MgCl2(aq) + H2 (g) Zn(s) + 2HCl(aq)  ZnCl2(aq) + H2 (g)

  4. Ideal Gas Law PV = n RT • R = “proportionality” constant = 0.08206 L atm  mol • P = pressure in atm • V = volume in liters • n = moles • T = temperature in Kelvins

  5. Standard ConditionsTemperature, Pressure & Moles • “STP” • For 1 mole of a gas at STP: • P = 1 atmosphere • T = C (273.15 K) • The molar volume of an ideal gas is 22.42 liters at STP

  6. Isobaric process: pressure constant Isochoric process: volume constant Isothermal process: temperature constant P1 V1 = P2 V2 V1 / n1 = V2 / n2 V1 / T1 = V2 / T2

  7. Hydrogen & the Ideal Gas Law n H2(g) = PV/ RT • n = moles H2(g) • P H2(g) = pressure of H2(g) in atm (mm Hg atm) • V = experimental volume (mL L) • T = experimental temperature (oC  K) Mg(s) + 2HCl(aq)  MgCl2(aq) + H2 (g) Zn(s) + 2HCl(aq)  ZnCl2(aq) + H2 (g)

  8. 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. PTotal = P1 + P2 + P3 + . . . PTotal n Total nTotal = n1 + n2 + n3 + . . .

  9. P H2(g) = P Total (barometric)- P H2O (g) [TABLE] - P HCl (g) P HCl (g) = HCl Height (mm) ÷ 12.95___________ Density Hg is 12.95 times > density HCl(aq) P HCl (g) = HCl Height (mm) x 0.0772___________ Density Hg is 12.95 times > density HCl(aq) 0.772 mm Hg/cm of acid solution

  10. Ideal Gas Law: Moles & Avogadro’s Law n H2(g) = PV/ RT • n = moles H2(g) • P H2(g) = pressure of H2(g) in atm (mm Hg atm) • P H2(g) = P Total (barometric)- P H2O (g)[TABLE] - P HCl (g) • V = experimental volume (mL L) • T = experimental temperature (oC  K) Mg(s) + 2HCl(aq)  MgCl2(aq) + H2 (g) Zn(s) + 2HCl(aq)  ZnCl2(aq) + H2 (g)

  11. Ideal Gas LawSimulator http://ch301.cm.utexas.edu/simulations/gas-laws/GasLawSimulator.swf

  12. Molar Mass of a Gas (Hydrogen) • PV = nRT • 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)

  13. QUESTION • Freon-12, CF2Cl2, a “safe” compressible gas, was widely used from 1935-1994 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 0.927 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? • 12.0 g/mol • 84 g/mol • 92.7 g/mol • 115 g/mol • 120. g/mol

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