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% Magnesium

% Magnesium. Mg(s) + 2HCl(aq)  MgCl 2 (aq) + H 2 (g). Zn(s) + 2HCl(aq)  ZnCl 2 (aq) + H 2 (g). Using the Ideal Gas Law & Partial Pressures Dr. Ron Rusay. What is wrong with this set up?. Mg(s) + 2HCl(aq)  MgCl 2 (aq) + H 2 (g).

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% Magnesium

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  1. % Magnesium 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?

  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 Temperature and Pressure • “STP” • For 1 mole of a gas at STP: • P = 1 atmosphere • T = C • The molar volume of an ideal gas is 22.42 liters at STP

  6. % Mg & 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) total moles H2(g) = moles Mg(s)+ moles Zn(s)

  7. Dalton’s Law of 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 + . . .

  8. 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)

  9. % Mg: Ideal Gas Law & Partial Pressure 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) total moles H2(g) = moles Mg(s)+ moles Zn(s)

  10. % Mg: Calculations Mg(s) + 2HCl(aq)  MgCl2(aq) + H2 (g) Zn(s) + 2HCl(aq)  ZnCl2(aq) + H2 (g) total moles H2(g) = moles Mg(s)+ moles Zn(s) mass (g) Zn(s) = mass sample (g) – ? mass Mg(s)(g) ? massMg(s) (g) (mass sample (g) – ? mass Mg(s)(g)) ___________ __________________________ Molar Mass Mg(s) Molar Mass Zn(s) total moles H2(g) = + Solve ? grams Mg(s) % Mg(s)

  11. Applications of the Ideal Gas Law • PV = nRT • n= g of gas/ MM gas [MM gas =g/mol] • PV = (g of gas/ MM gas )RT • MM gas = g of gas(RT)/PV • MM gas = g of gas/V (RT/P) • MM gas = density of gas (RT/P)

  12. QUESTION Freon-12 had been widely used as a refrigerant in air conditioning systems. However, it has been shown to be a greenhouse gas and destroy the ozone layer. What is the molar mass of Freon-12 if 9.27 grams was collected by water displacement, in a 2.00 liter volume at 30.0°C and 764 mmHg. Water’s vapor pressure at this temperature is approximately 31.8 mmHg. A) 120. g/mol B) 12.0 g/mol C) 115 g/mol D) 92.7 g/mol

  13. ANSWER • is the molar mass of Freon-12. The pressure must be corrected for the presence of water by subtracting 31.8 mmHg from the total pressure. This should also be converted to atm. The temperature must be converted to K. Then PV = nRT can be used if n is written as g/mm and solved for mm.

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