http chemconnections orggeneralchem 108MagnesiumZincwo 1 mov Experimentally Determining

http: //chemconnections. org/general/chem 108/Magnesium-Zinc-wo. 1. mov Experimentally Determining Moles of Hydrogen Mg(s) + 2 HCl(aq) Mg. Cl 2(aq) + H 2 (g) Zn(s) + 2 HCl(aq) Zn. Cl 2(aq) + H 2 (g) Using Partial Pressures the Ideal Gas Law & Stoichiometry Dr. Ron Rusay

What is wrong with this set up? Mg or Zn

Mg(s) + 2 HCl(aq) Mg. Cl 2(aq) + H 2 (g) Zn(s) + 2 HCl(aq) Zn. Cl 2(aq) + H 2 (g)

Mg or Zn

Ideal Gas Law PV = n RT • • • R = “proportionality” constant = 0. 08206 L atm mol P = pressure of gas in atm V = volume of gas in liters n = moles of gas T = temperature of gas in Kelvin

Standard Conditions Temperature, 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

Isobaric process: pressure constant Isochoric process: volume constant Isothermal process: temperature constant P 1 V 1 = P 2 V 2 P V V 1 / n 1 = V 2 / n 2 V n V 1 / T 1 = V 2 / T 2 V T Standard Conditions (STP) 273 K, 1. 0 atm, R = 0. 08206 L atm/ K mol @STP 1 mole of any “ideal” gas has A volume of 22. 4 Liters.

Hydrogen & the Ideal Gas Law n H (g) = PV / RT 2 • • n = moles H 2(g) P H 2(g) = pressure of H 2(g) in atm (mm Hg atm) V = experimental volume (m. L L) T = experimental temperature (o. C K) Mg(s) + 2 HCl(aq) Mg. Cl 2(aq) + H 2 (g) Zn(s) + 2 HCl(aq) Zn. Cl 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. PTotal = P 1 + P 2 + P 3 +. . . PTotal n Total n. Total = n 1 + n 2 + n 3 +. . .

• P H 2(g) = P Total (barometric) - P H 2 O (g) [TABLE] - P HCl (g) = HCl Height (mm) ÷ 12. 95 ______ HCl Height (mm) x 0. 0772 ______ Density Hg is 12. 95 times > density HCl(aq) 0. 772 mm Hg/cm of acid solution

Ideal Gas Law: Moles / Avogadro’s Law n H (g) = PV / RT 2 • • • 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 (m. L L) T = experimental temperature (o. C K) R = 0. 082057338 L atm K− 1 mol− 1 (constant) Mg(s) + 2 HCl(aq) Mg. Cl 2(aq) + H 2 (g) Zn(s) + 2 HCl(aq) Zn. Cl 2(aq) + H 2 (g)

Stoichiometry Theoretical Moles Hydrogen (Part I: Zinc Calculation) n H (g) = n Zn(s) 2 Zn(s) + 2 HCl(aq) Zn. Cl 2(aq) + H 2 (g) mass (g) Zn(s) = mass sample (g) = 0. 2100 g moles H 2(g) = moles Zn(s) = = mass sample (g) _____________________ Molar Mass Zn(s) 0. 2100 g Zn(s) _____________________ 65. 39 g/mol Zn(s) = 0. 003211 moles Zn(s)

Moles : Ideal Gas Law (Part I: Hydrogen Calculation) Zn(s) + 2 HCl(aq) Zn. Cl 2(aq) + H 2 (g) n H (g) = PV / RT 2 • • • 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 (m. L L) T = experimental temperature (o. C K)

Moles : Ideal Gas Law (Part I: Hydrogen Calculation) Zn(s) + 2 HCl(aq) Zn. Cl 2(aq) + H 2 (g) n H (g) = PV / RT 2 • • • n = moles H 2(g) P H 2(g) = pressure of H 2(g) in atm (mm Hg atm) P H 2(g) = 29. 98 inches Hg (barometric) - 19. 8 mm Hg H 2 O (g) [TABLE] - P HCl (g) V = 81. 5 m. L (m. L L) P HCl (g) T = 22. 0 o. C (o. C K) R = 0. 082057338 L atm K− 1 mol− 1 19. 2 cm 10. 0 cm

• P H 2(g) = P Total (barometric) - P H 2 O (g) [TABLE] - P HCl (g) = 19. 2 cm Hg - 10. 0 cm Hg = 92 mm Hg HCl Height (mm) x 0. 0772 HCl Height (mm) ÷ 12. 95 = 7. 1 mm Hg ______ = 7. 1 mm Hg _____ Density Hg is 12. 95 times > density HCl(aq) 0. 772 mm Hg/cm of acid solution

Moles : Ideal Gas Law (Part I: Hydrogen Calculation) Zn(s) + 2 HCl(aq) Zn. Cl 2(aq) + H 2 (g) n H (g) = PV / RT = 0. 00325 moles H (g) 2 • • • 2 n = moles H 2(g) P H 2(g) = pressure of H 2(g) in atm (mm Hg atm) P H 2(g) = 761. 5 mm Hg (barometric) - 19. 8 mm Hg H 2 O (g) 7. 1 mm Hg HCl (g) = 734. 6 mm Hg • = 0. 9666 atm P HCl (g) • V = 0. 0815 L • T = 295. 1 K 19. 2 cm 10. 0 R = 0. 08206 L atm K− 1 mol− 1 cm

% Error Theoretical Moles Hydrogen vs. Experimental (Part I: Calculation) Zn(s) + 2 HCl(aq) Zn. Cl 2(aq) + H 2 (g) mass (g) Zn(s) = mass sample (g) = 0. 2100 g = 0. 003211 moles H 2(g) theoretical % Error = experimental moles H 2(g) - theoretical moles H 2(g) _____________________________________________________--________ theoretical moles H 2(g = = 0. 00325 moles - 0. 003211 moles ________________________________________ 0. 003211 moles 1. 32 % x 100

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 • MM gas = g of gas/V (RT/P) • MM gas = density of gas (RT/P)