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

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Unformatted text preview: 11/6/12 Lab 10 PreLab -‐‑ Acid-‐‑Base Studies WebAssign Lab 10 PreLab -­ Acid-­Base Studies (Prelab) Current Score : 12 / 25 Steve Yarush CH102, section 021, Fall 2012 Instructor: Brandon Zoellner Due : Monday, November 5 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 1. 3/3 points | Previous Answers NCSUGenChem102LabV1 10.PRE.01. Green checks and red X's are not displayed for this question. These items concern safety in the Acid-­Base Studies Experiment. (a) Select all of the following that are listed as corrosive. (Select all that apply.) acetic acid (HC2H3O2) ammonia (NH3) hydrochloric acid (HCl) sodium hydroxide (NaOH) water (H2O) (b) Select all of the following which might give off highly irritating vapors. (Select all that apply.) acetic acid (HC2H3O2) ammonia (NH3) hydrochloric acid (HCl) sodium hydroxide (NaOH) water (H2O) (c) Because acid-­base reactions are highly exothermic, which of the following should you NOT mix together? www.webassign.net/web/Student/Assignment-‐‑Responses/last?dep=4450410 1/7 11/6/12 Lab 10 PreLab -‐‑ Acid-‐‑Base Studies any acidic solutions with any basic solutions any two acidic solutions any two basic solutions solutions with concentrations greater than 0.1 M solutions with concentrations less than 0.1 M any acidic or basic solution with water Acid-­Base Studies 2. 2/2 points | Previous Answers NCSUGenChem102LabV1 10.PRE.02. What should be done with the waste from the Acid-­Base Studies experiment? Basic solutions can be flushed down the sink with water but the acidic solutions must be placed in the labeled waste container. All solutions can be flushed down the sink with plenty of water. No waste solutions will be generated in this lab. All solutions must be placed in the labeled waste container. Acidic solutions can be flushed down the sink with water but the basic solutions must be placed in the labeled waste container. Acid-­Base Studies 3. 5/5 points | Previous Answers NCSUGenChem102LabV1 10.PRE.03. Green checks and red X's are not displayed for this question. Conjugate acid-­base pairs differ by which one of the following? www.webassign.net/web/Student/Assignment-‐‑Responses/last?dep=4450410 2/7 11/6/12 Lab 10 PreLab -‐‑ Acid-‐‑Base Studies a hydronium ion a hydroxide ion a hydronium or hydroxide ion an electron an oxyanion a proton Which of the following solutions is not used in this experiment? 0.010 M nitric acid 0.010 M acetic acid 0.0010 M HCl 0.010 M HCl 0.00010 M HCl 0.01 M NaOH Acidic solutions have a hydronium concentration, [H3O+ ] that is which of the following? > 10−7 M < 10−7 M = 10−7 M smaller than the hydroxide ion concentration 7% in strength A solution's pH is a measure of what? www.webassign.net/web/Student/Assignment-‐‑Responses/last?dep=4450410 3/7 11/6/12 Lab 10 PreLab -‐‑ Acid-‐‑Base Studies strength or weakness acid dissociation constant hydronium ion concentration molarity percent composition Which of the following is true about weak acids? They have a large Ka and dissociate 100%. They have a small Ka and dissociate to only a small degree. They do not dissociate. They lose all of their protons when they react. They gain one and only one proton. Acid-­Base Studies www.webassign.net/web/Student/Assignment-‐‑Responses/last?dep=4450410 4/7 11/6/12 Lab 10 PreLab -‐‑ Acid-‐‑Base Studies 4. 2/2 points | Previous Answers NCSUGenChem102LabV1 10.PRE.04. Green checks and red X's are not displayed for this question. A student has two solutions of 0.10 M acid labeled just as A and B. The pH of one solution was found to be 1.02 and the other 4.73. One is a strong acid and one is a strong base. One is a weak acid and one is a weak base. Both are weak acids. Both are strong acids. You cannot tell the strength of an acid from pH readings. One is a strong acid and one is a weak acid. You cannot tell the strength of an acid without measuring the pH of diluted solutions. One is a strong acid and one is a weak base. HX and HY are weak acids, but HX is a stronger acid than HY. What result would you expect if you measured the pH of 0.1 M solutions of HX and HY? HY would have a lower pH than HX. HX would have a lower pH than HY. You cannot predict without making dilutions. They would have the same pH because they are both weak acids. Acid-­Base Studies 5. –/9 points NCSUGenChem102LabV1 10.PRE.05. Acids react with water to produce hydronium ions, H3O+. The strength of an acid relative to water is quantified by the equilibrium constant for this reaction, called the Ka value. This K value is defined as any other equilibrium value, as [products]coefficient/[reactants]coefficient. Values for Ka can be found at the Table of Physical Data. Answer the following questions that apply to a strong acid. www.webassign.net/web/Student/Assignment-‐‑Responses/last?dep=4450410 5/7 11/6/12 Lab 10 PreLab -‐‑ Acid-‐‑Base Studies (a) Write the net acid-­base reaction that occurs when HCl is added to water. (Use the lowest possible coefficients. Omit states-­of-­matter in your answer.) HCl + H2O → H3O+ + Cl -­ No Response (b) What is the relative Ka value for this reaction? Ka ≈ 1 Ka >> 1 Ka << 1 (c) Which are the only species present? water molecules hydronium ions strong acid molecules conjugate base ions (d) Which statements are true when a strong acid, such as HCl, is dissolved in water? (Select all that apply.) The only species present are hydronium, and the conjugate base, Cl ‾. Ka ~ 1 Equal amounts of strong acid and hydronium exist in solution. Ka >> 1 Answer the following questions that apply to a weak acid. (e) Write the net acid-­base reaction that occurs when HF is added to water. HF + H2O → H3O+ + F-­ No Response (f) What is the relative Ka value for this reaction? (See the Acid Base Table.) Ka ≈ 1 Ka << 1 www.webassign.net/web/Student/Assignment-‐‑Responses/last?dep=4450410 6/7 11/6/12 Lab 10 PreLab -‐‑ Acid-‐‑Base Studies Ka >> 1 (g) Which species are present in the greatest concentration? (Select all that apply.) hydronium ions weak acid molecules conjugate base ions water molecules Acid-­Base Studies 6. –/4 points NCSUGenChem102LabV1 10.PRE.06. In lab, you will be measuring the pH of ionic solids that have been dissolved in water. (a) Write the dissolution reaction for solid Na2CO3 below. (Use the lowest possible coefficients. Include states-­of-­matter under the given conditions in your answer.) Na2CO3(s) → 2 Na+(aq) + CO32-­(aq) No Response (b) Once the ionic solid has dissolved, the anion that is formed is able to react as a base, with water as the acid. Write the net acid-­base reaction that occurs when dissolved Na2CO3 reacts with water. (Use the lowest possible coefficients. Omit states-­of-­matter in your answer.) H2O + CO32-­ → OH-­ + HCO3-­ or 2 H2O + CO32-­ → 2 OH-­ + H2CO3 No Response Acid-­Base Studies www.webassign.net/web/Student/Assignment-‐‑Responses/last?dep=4450410 7/7 ...
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