Preview of “Lab 10 PostLab - Acid-Base Studies”

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Unformatted text preview: 12/5/12 Lab 10 PostLab -‐‑ Acid-‐‑Base Studies Steve Yarush CH102, section 021, Fall 2012 Instructor: Brandon Zoellner WebAssign Lab 10 PostLab -­ Acid-­Base Studies (Postlab) Current Score : 24.5 / 25 Due : Thursday, November 8 2012 11:00 PM EST The due date for this assignment is past. Your work can be viewed below, but no changes can be made. Important! Before you view the answer key, decide whether or not you plan to request an extension. Your Instructor may not grant you an extension if you have viewed the answer key. Automatic extensions are not granted if you have viewed the answer key. Request Extension View Key 1. 5/5 points | Previous Answers NCSUGenChem102LabV1 10.POST.01. Green checks and red X's are not displayed for the multiple select and multiple choice portions of this question. What is the pH of 0.039 M HCl? 1.41 The pH of 0.039 M HC2H3O2 is 3.08. Why don't the two equimolar solutions of HCl and HC2H3O2 have the same pH? (Select all that apply.) At equilibrium, the HC2H3O2 solution contains mainly undissociated HC2H3O2 and only small amounts of H3O+. At equilibrium, the HCl solution contains mainly undissociated HCl and only small amounts of H3O+. The Ka of HC2H3O2 is smaller than that of HCl, so at equilibrium the concentration of H3O+ ions in a HC2H3O2 solution is less than in a HCl solution of the same concentration. The Ka of HC2H3O2 is greater than that of HCl, so at equilibrium the concentration of H3O+ ions in a HC2H3O2 solution is less than in a HCl solution of the same concentration. The conjugate base of HC2H3O2, C2H3O2−, generates OH− ions in solution, thus lowering the total concentration of H3O+ ions. What is the hydronium ion concentration in a solution with pH = 2.11? 7.8e-­3 M An unknown bottle of acid says 0.0010 M on the label. The measured pH is 3.00. This implies that www.webassign.net/web/Student/Assignment-‐‑Responses/last?dep=4450464 1/7 12/5/12 Lab 10 PostLab -‐‑ Acid-‐‑Base Studies the unknown acid has which of the following? Ka >> 1 Ka << 1 Ka ≈ 1 Which of the acids below will have the lowest pH in a 0.0010 M solution of the acid? (Hint: Larger Ka values favor products and smaller Ka values favor reactants.) HClO HCO3− HNO2 HSO4− Acid-­Base Studies 2. 6/6 points | Previous Answers NCSUGenChem102LabV1 10.POST.02. Write net Brønsted equations that show the acidic or basic nature of the following solutions in water. For polyprotic species (vitamin C, lemon juice, and washing soda), show only one proton transfer. Remember that spectator ions are not included. (Use the lowest possible coefficients. Omit states-­of-­matter in your answer.) (a) vinegar (acetic acid, HC2H3O2) HC2H3O2 + H2O → C2H3O2-­ + H3O+ HC_2H_3O_2 + H_2O -‐‑-‐‑> C_2H_3O_2^-‐‑ + H_3O^+ (b) bleach (sodium hypochlorite, NaOCl) OCl -­ + H2O → OH-­ + HClO OCl^-‐‑ + H_2O -‐‑-‐‑> OH^-‐‑ + HClO (c) ammonia (NH3) www.webassign.net/web/Student/Assignment-‐‑Responses/last?dep=4450464 2/7 12/5/12 Lab 10 PostLab -‐‑ Acid-‐‑Base Studies NH3 + H2O → OH-­ + NH4+ NH_3 + H_2O -‐‑-‐‑> OH^-‐‑ + NH_4^+ (d) Vitamin C (ascorbic acid, H2C6H6O6) H2C6H6O6 + H2O → HC6H6O6-­ + H3O+ H_2C_6H_6O_6 + H_2O -‐‑-‐‑> HC_6H_6O_6^-‐‑ + H_3O^+ (e) lemon juice (citric acid, H3C6H5O7) H3C6H5O7 + H2O → H2C6H5O7-­ + H3O+ H_3C_6H_5O_7 + H_2O -‐‑-‐‑> H_2C_6H_5O_7^-‐‑ + H_3O^+ (f) washing soda (sodium carbonate, Na2CO3) CO 2-­ 3 + H2O → OH-­ + HCO3-­ CO_3^2-‐‑ + H_2O -‐‑-‐‑> OH^-‐‑ + HCO_3^-‐‑ Acid-­Base Studies www.webassign.net/web/Student/Assignment-‐‑Responses/last?dep=4450464 3/7 12/5/12 Lab 10 PostLab -‐‑ Acid-‐‑Base Studies 3. 2/2 points | Previous Answers NCSUGenChem102LabV1 10.POST.03. Two net Brønsted equations show why carbonated water, such as that found in sodas, is acidic. (a) Show the reaction of CO2 with water to produce carbonic acid (H2CO3). (Use the lowest possible coefficients. Omit states-­of-­matter in your answer.) CO2 + H2O → H2CO3 CO_2 + H_2O -‐‑-‐‑> H_2CO_3 (b) Show the reaction of the carbonic acid with water. H2CO3 + H2O → HCO3-­ + H3O+ H_2CO_3 + H_2O -‐‑-‐‑> HCO_3^-‐‑ + H_3O^+ Acid-­Base Studies www.webassign.net/web/Student/Assignment-‐‑Responses/last?dep=4450464 4/7 12/5/12 Lab 10 PostLab -‐‑ Acid-‐‑Base Studies 4. 1.5/2 points | Previous Answers NCSUGenChem102LabV1 10.POST.04. During the lab, you measured the pH of common household items. Write net Brønsted equations that show the acidic or basic nature of the following substances, given the pH. For polyprotic acids, only show one proton transfer. Remember that spectator ions are not included. (Use the lowest possible coefficients. Omit states-­of-­matter in your answer.) (a) coffee (quinic acid, HC7H11O6) with a pH of 4.70 HC7H11O6 + H2O H3O+ + C7H11O6-­ HC_7H_11O_6 + H_2O <=> H_3O^+ + C_7H_11O_6^-‐‑ (b) tums antacid (calcium carbonate) with a pH of 8.50 CO 2-­ 3 + H2O HCO3-­ + OH-­ CO_3^-‐‑2 + H_2O <=> HCO_3^-‐‑ + OH^-‐‑ (c) fish (trimethylamine, C3H9N) with a pH of 8.20 C3H9N + H2O HC3H9N+ + OH-­ C_3H_9N + H_2O <=> HC_3H_9N^+ + OH^-‐‑ (d) lithium hydrogensulfide with a pH of 9.90 HS-­ + H2O H2S + OH-­ HS^-‐‑ + H_2O <=> H_2S + OH^-‐‑ Acid-­Base Studies 5. 8/8 points | Previous Answers NCSUGenChem102LabV1 10.POST.05. Green checks and red X's are not displayed for the multiple choice portion of this question. In part C of the experiment, a student begins with a beaker containing 10.0 mL of 0.010 M HCl solution and adds different volumes of 0.010 M NaOH. (a) How many millimoles of acid are initially in the beaker? (If in doubt, look back at your calculation from experiment 9). 0.10 mmol H3O+ www.webassign.net/web/Student/Assignment-‐‑Responses/last?dep=4450464 5/7 12/5/12 Lab 10 PostLab -‐‑ Acid-‐‑Base Studies (b) Fill in the table below with mmol of NaOH added and the relative concentrations of H3O+ and OH − in each solution. mL NaOH mmol OH − added pH concentration [H3O+ ] >> [OH – ] 0.0 0 2.00 [H3O+ ] ≈ [OH – ] [H3O+ ] << [OH – ] [H3O+ ] >> [OH – ] 3.0 3.0e-­2 2.27 [H3O+ ] ≈ [OH – ] [H3O+ ] << [OH – ] [H3O+ ] >> [OH – ] 6.0 6.0e-­2 2.60 [H3O+ ] ≈ [OH – ] [H3O+ ] << [OH – ] [H3O+ ] >> [OH – ] 12.0 .12 10.96 [H3O+ ] ≈ [OH – ] [H3O+ ] << [OH – ] (c) What would the approximate pH of the solution be after the addition of 10.0 mL of 0.010 M NaOH? www.webassign.net/web/Student/Assignment-‐‑Responses/last?dep=4450464 6/7 12/5/12 Lab 10 PostLab -‐‑ Acid-‐‑Base Studies 1.0 7.0 10.0 14.0 Acid-­Base Studies 6. 2/2 points | Previous Answers NCSUGenChem102LabV1 10.POST.06. During lab you measured the pH of mixtures containing strong acid and strong base. Write net Brønsted equations that show the acid-­base reactions of common household items. For polyprotic species (such as vitamin C, lemon juice, and washing soda), please show only one proton transfer. Remember that spectator ions are not included. (Use the lowest possible coefficients. Omit states-­ of-­matter in your answer.) (a) bleach and vinegar (sodium hypochlorite and HC2H3O2) HC2H3O2 + ClO1-­ → C2H3O 1-­ 2 + HClO HC_2H_3O_2 + ClO^1-‐‑ -‐‑-‐‑> C_2H_3O_2^1-‐‑ + HClO (b) Vitamin C and ammonia (H2C6H6O6 and NH3) H2C6H6O6 + NH3 → HC6H6O6-­ + NH4+ H_2C_6H_6O_6 + NH_3 -‐‑-‐‑> HC_6H_6O_6^-‐‑ + NH_4^+ Acid-­Base Studies www.webassign.net/web/Student/Assignment-‐‑Responses/last?dep=4450464 7/7 ...
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  • Vitamin  C, Previous  Answers, lowest  possible  coefficients, Acid-‐‑Base Studies, Acid-­Base  Studies

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