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Chem 108: Lab Week 15

Chem 108: Lab Week 15. Sign in Note your Group # Pick up Papers and Handout. Chem 108: Lab Week 15. Sit with your Group Pick up calculator for your group. ANSWER. The [H + ] was determined to be 3.5  10 –6. B. pH = -log [H 3 O + ] = -log [H + ] pH = -log [ 3.5  10 –6 ] Then:

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Chem 108: Lab Week 15

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  1. Chem 108: LabWeek 15 Sign in Note your Group # Pick up Papers and Handout

  2. Chem 108: LabWeek 15 Sit with your Group Pick up calculator for your group

  3. ANSWER The [H+] was determined to be 3.5  10–6 B. pH = -log [H3O+] = -log [H+] pH = -log [3.5  10–6] Then: 14.00 = pH + pOH can be used to obtain the pOH. Finally, [OH–] = 10–pOH. pH = 5.46 ; pOH = 8.54; [OH–] = 2.9  10–9 M Kw = 1.00  1014 = [H+] [OH] = [H3O+] [OH] Kw = 10–pH x 10–pOH pKw = 14.00 = pH + pOH

  4. ANSWER The [H+] was determined to be 3.5  10–6 B. pH = -log [H3O+] = -log [H+] pH = -log [3.5  10–6] • Keystrokes • (-) • LOG • 3.5 • 2nd • EE (x-1) • (-) • 6 -log(3.5E-6

  5. ANSWER The [H+] was determined to be 3.5  10–6 B. pH = -log [H3O+] = -log [H+] pH = -log [3.5  10–6] • Keystrokes • (-) • LOG • 3.5 • 2nd • EE (x-1) • (-) • 6 • = ENTER -log(3.5E-6 5.455931956

  6. ANSWER pH = -log [3.5  10–6] = 5.46 pOH = 14.00 – 5.46 = 8.54 [OH–] = ? • Keystrokes • 2nd • 10 x (LOG) • (-) • 8.54 • = ENTER 10^(-8.54 0.000000003 [OH–] = 3  10–9 M

  7. The pH Scale

  8. Chem 108: Lab Due Today: Acid-Base Titration Complete Individual Report form pp.94-96. Include clear calculations with units. 0.2162 mol/L

  9. Unkown Acid NeutralizationNet Ionic Equation/ Calculation HNO3(aq) +NaOH (aq) NaNO3(aq) + H2O(l) acid base salt water conj. acid conj. base acid base water • 25.00 mL of MH+ aq= ? (unknown acid solution) was titrated with a sodium hydroxide solution, MOH-= ? 0.2162 M. It required 24.20 mL as an average of three trials which were within +/- 0.20 mL to reach a faint pink color. • MH+ aq = ? H+(aq) + OH -(aq) H2O(l)

  10. Unkown Acid NeutralizationNet Ionic Equation/ Calculation acid base water • 25.00 mL of MH+ aq= ? (unknown acid solution) was titrated with a sodium hydroxide solution, MOH-= ? 0.2162 M. It required 24.20 mL as an average of three trials which were within +/- 0.20 mL to reach a faint pink color. ?MH+= [MOH- x VOH- / VH+ ] [? molH+ / ? molOH-] 0.2162molOH- x 0.02420LOH- x 1 molH+ LOH- x0.02500LH+x 1 molOH- = = 0.2093 MH+ H+(aq) + OH -(aq) H2O(l)

  11. QUESTION A 35.00 mL sample of a monoprotic acid of unknown concentration was titrated with 42.30 mL of 0.2250 M KOH. What is the concentration of the unknown acid? 0.0930 M 0.3030 M 0.2719 M 0.1860 M 0.3720 M

  12. Answer A 35.00 mL sample of a monoprotic acid of unknown concentration was titrated with 42.30 mL of 0.2250 M KOH. What is the concentration of the unknown acid? 0.0930 M 0.3030 M 0.2719 M 0.1860 M 0.3720 M 0.2250molOH- x 0.04230LOH- x 1 molH+ LOH- x0.03500LH+x 1 molOH- H+(aq) + OH -(aq) H2O(l) = ?MH+= [MOH- x VOH- / VH+ ] [1 molH+ / 1 molOH-]

  13. Join with your Group members In completing the handout Stoichiometry / Limiting Reactant / Ideal Gas Law http://chemconnections.org/general/chem108/Gas-Limiting%20Reactant-demo.2018.pdf Acid-Base Reactions & Behavior of Gases

  14. Stoichiometry / Limiting Reactant / Ideal Gas Law Acid-Base Reactions & Behavior of Gases 2.00 g / 4.00 g / 6.00 g 70.0mL 1.0 M HCl w/ phenolphthalein

  15. Stoichiometry / Limiting Reactant / Ideal Gas Law Acid-Base Reactions & Behavior of Gases Follow the accompanying slides. Complete the handout.

  16. Stoichiometry / Limiting Reactant / Ideal Gas Law 1 1 1 1 1 Acid-Base Reactions & Behavior of Gases

  17. Acid-Base Reactions & Behavior of Gases Molar Mass = 84.00 g/mol Stoichiometry / Limiting Reactant / Ideal Gas Law molHCl = 1.0 mol/L x 1.00L/1,000mL x 70.0mL mol = 2.00 g / 84.00 g/mol mol = 4.00 g / 84.00 g/mol mol = 6.00 g / 84.00 g/mol

  18. Bring completed Report Forms to Dr. R. to get Mg(s) sample(s). Gas Stoichiometry

  19. Refer to the Procedure section pp. 54-56. The following slides correspond to the instructions in the procedure.

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

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

  22. Mg or Zn

  23. Refer to the Gas Stoichiometry Report Form, pg. 58-59 • Experimental data is to be obtained for the reaction of a known mass of magnesium metal: • The volume of hydrogen, pressure and temperature determined and recorded. • Moles of hydrogen is calculated using Ideal Gas Law calculations, then calculating mass of the starting magnesium from the number of moles of hydrogen. Mg(s) + 2HCl(aq)  MgCl2(aq) + H2 (g)

  24. BackgroundIdeal 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

  25. 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

  26. Isobaric process: pressure constant Isochoric process: volume constant Isothermal process: temperature constant P1 V1 = P2 V2 P V V1 / n1 = V2 / n2 V n 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. Combined Gas Law P1V1 / T1 = P2V2 / T2 V1 / T1 = V2 / T2 V T

  27. 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)

  28. 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 + . . .

  29. 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

  30. 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) • R =0.082057338L atm K−1 mol−1 (constant) Mg(s) + 2HCl(aq)  MgCl2(aq) + H2 (g) Zn(s) + 2HCl(aq)  ZnCl2(aq) + H2 (g)

  31. Zn(s) + 2HCl(aq)  ZnCl2(aq) + H2 (g) • Refer to Report Form Part I: (Example uses Zinc.) Mole Calculations: • Stoichiometry Calculation • Ideal Gas Law Calculations • Comparison (% Error)

  32. StoichiometryMoles Hydrogen / Mass of Zinc (Part I: Zinc Calculation) mol H2(g) = mol Zn(s) Zn(s) + 2HCl(aq)  ZnCl2(aq) + H2 (g) mass (g) Zn(s) = mol Zn(s) x Molar Mass Zn(s)

  33. Zinc Example Calculation Zn(s) + 2HCl(aq)  ZnCl2(aq) + H2 (g) • Complete Report Form pg. 58 Part I: Mole Calculations: • Stoichiometry Calculation • Ideal Gas Law Calculations • Comparison (% Error)

  34. Moles : Ideal Gas Law(Part I: Zinc Calculation Example) Zn(s) + 2HCl(aq)  ZnCl2(aq) + H2 (g) 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) R =0.082057338L atm K−1 mol−1

  35. Moles : Ideal Gas Law(Part I: Zinc Calculation Example) Zn(s) + 2HCl(aq)  ZnCl2(aq) + H2 (g) n H2(g) = PV/ RT V = experimental volume (mL L) R =0.082057338L atm K−1 mol−1

  36. Moles : Ideal Gas Law(Part I: Zinc Calculation Example) Zn(s) + 2HCl(aq)  ZnCl2(aq) + H2 (g) n H2(g) = PV/ RT V = experimental volume (mL L) T = experimental temperature (oC  K) R =0.082057338L atm K−1 mol−1

  37. Moles : Ideal Gas Law(Part I: Zinc Calculation Example) Zn(s) + 2HCl(aq)  ZnCl2(aq) + H2 (g) n H2(g) = PV/ RT V = experimental volume (mL L) T = experimental temperature (oC  K) 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) R =0.082057338L atm K−1 mol−1

  38. Moles : Ideal Gas LawPart I: Hydrogen Calculation, (Refer to Form’s Data) Zn(s) + 2HCl(aq)  ZnCl2(aq) + H2 (g) n H2(g) = PV/ RT • n = moles H2(g) • P H2(g) = pressure of H2(g) in atm (mm Hg atm) • P H2(g) = 29.98inches Hg (barometric)-19.8mm Hg H2O (g)[TABLE] - P HCl (g) P HCl (g) 19.2 cm R =0.082057338L atm K−1 mol−1 10.0 cm

  39. P H2(g) = P Total (barometric)- P H2O (g) [TABLE] - P HCl (g) P HCl (g) = 19.2 cm Hg - 10.0 cm Hg = 92 mm Hg HCl Height (mm) x 0.0772 = 7.1 mm Hg __________ Density Hg is 12.95 times > density HCl(aq) P HCl (g) = 19.2 cm Hg - 10.0 cm Hg = 92 mm Hg HCl Height (mm) ÷ 12.95 = 7.1 mm Hg ___________ Density Hg is 12.95 times > density HCl(aq) P HCl (g) 0.772 mm Hg/cm of acid solution

  40. P H2(g) = 761.5mm Hg (barometric) -19.8mm Hg H2O (g)-7.1mm Hg HCl (g) = 734.6mm Hg = 734.6mm Hg / 760.0mm Hg / 1.000 atm = 0.9666 atm

  41. Moles : Ideal Gas Law(Part I: Hydrogen Calculation) Zn(s) + 2HCl(aq)  ZnCl2(aq) + H2 (g) n H2(g) = PV/ RT • n = moles H2(g) • P H2(g) = 0.9666 atm • V = 0.0815 L • T = 295.1K R =0.08206L atm K−1 mol−1 n H2(g) = 0.00325 moles H2(g) = 0.00325moles Zn(s)

  42. % ErrorTheoretical Mass Zinc vs. Experimental(Part I: Calculation) Zn(s) + 2HCl(aq)  ZnCl2(aq) + H2 (g) mass (g) Zn(s) = mol Zn(s) x Molar Mass Zn(s) = 0.00325 moles Zn(s)x 65.37 g/mol Zn(s) experimental grams Zn(s)- theoretical grams Zn(s) _________________________________________________________________________________________________________--________________ theoretical grams Zn(s) x 100 % Error = 0.213g - 0.21 g ___________________________________________________ 0.21 g x 100 = = 1.4 %

  43. Molar Mass of any Gas (Hydrogen for example) • 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 • MM gas = g of gas/V (RT/P) • MM gas = density of gas (RT/P)

  44. (Part II) Magnesium Mg(s) + 2HCl(aq)  MgCl2(aq) + H2 (g) Mole Calculations: • Stoichiometry Calculation • Ideal Gas Law Calculations • Comparison (% Error) Get equipment from stockroom and complete data acquisition for Part II. Have individual Report Forms checked before leaving lab today.

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