CK-12 Chemistry Concepts - Intermediate Answer Key Chapter 21: Acids & Bases 21.1 Properties of Acids Practice Questions Watch the video at the link below and answer the following questions: http://www.youtube.com/watch?v=uahCEZf831c 1. Which of the four solutions are acids? 2. Stop the video at 0:30 minutes and predict conductivities. 3. What color did the acids turn when universal indicator was added? Answers 1. HCl and CH3COOH (acetic acid). 2. The acids and NaCl are ionized and will conduct electricity. 3. Red. Review Questions 1. Are all acids electrolytes in water? 2. What color does blue litmus turn in the presence of an acid? 3. What does the reaction of an acid and a base produce? Answers 1. Yes. 2. Red. 3. Water and a salt. 21.2 Properties of Bases Practice Questions 1 Read the material at the site below and answer the following questions: https://sites.google.com/site/sodiumhydroxsite/Acidsandbasesbasics/chemical- properties-of-bases 1. What does the reaction between an acid and a base produce? 2. What is this reaction called? 3. What does the reaction of a base with an ammonium salt form? Answers 1. A salt and water. 2. Neutralization. 3. A metal salt, ammonia, and water. Review Questions 1. Are bases electrolytes? 2. What color does a base turn phenolphthalein? 3. Do bases react with metals the same way that acids do? Answers 1. Yes, some are strong electrolytes and some are weak. 2. Red. 3. No. 21.3 Arrhenius Acids Practice Read the material at the link below and answer the following questions: http://dwb4.unl.edu/Chem/CHEM869R/CHEM869RLinks/www.nidlink.com/7Ejfromm/arr henius.htm 1. What was Arrhenius’ first scientific idea? 2. What did his Ph.D committee think about it? 3. What did he win for this idea? 4. Write the generic equation for dissociation of an Arrhenius acid. Answers 1. Electrolytes dissociated in solution. 2. They did not like it and gave him a D for his research. 2 3. The 1903 Nobel Prize in Chemistry. 4. HA → H+ + A-. Review Questions 1. What is an Arrhenius acid? 2. What is a hydronium ion? 3. Is H2SO4 a monoprotic or a polyprotic acid? Answers 1. Yields a hydrogen ion upon dissociation in water. + 2. H3O . 3. Polyprotic. 21.4 Arrhenius Bases Practice Questions Read the material at the link below and then take the quiz: http://flatworldknowledge.lardbucket.org/books/introductory- chemistry/section_16_01.html Answers Answers are at the web site. Review Questions 1. What is an Arrhenius base? 2. What is one reaction that will form an Arrhenius base? 3. Are alkaline earth bases very water-soluble? Answers 1. One that forma a hydroxide ion in water solution. 2. Alkali metal + water → base + hydrogen gas. 3. No, they only partially ionize. 3 21.5 Bronsted-Lowry Acids and Bases Practice Questions Read the material at the link below and answer the following questions: http://www.chemteam.info/AcidBase/Bronsted-Lowry-AcidBase.html 1. Why is water considered a base in the reaction between water and HCl? + 2. Why is H3O considered an acid? 3. Why is the chloride anion considered a base? Answers 1. Because it can accept a proton from the HCl to form the hydronium ion. 2. Because it can donate a proton. 3. Because it can accept a proton to form HCl. Review Questions 1. What is a Brønsted-Lowry acid? 2. What is a Brønsted-Lowry base? 3. How does ammonia function as a Brønsted-Lowry base? Answers 1. A molecule or ion that donates a proton. 2. A molecule or ion that accepts a proton. 3. The lone pair electrons on the N atom can accept a proton. 21.6 Bronsted-Lowry Acid-Base Reactions Practice Questions Read the material at the link below and do the problems at the end of the selection: http://s-owl.cengage.com/ebooks/vining_owlbook_prototype/ebook/ch16/Sect16-1- b.html 4 Answers Answers are on the web site. Review Questions 1. In the reaction between ammonia and water, how does the ammonia serve as a base on the left-hand side of the equation? 2. How does the ammonium ion serve as an acid on the right-hand side of the equation? 3. Write the conjugate acid-base pairs for the reaction between two water molecules illustrated above. Answers 1. It accepts a proton. 2. It donates a proton. + - 3. H2O/H3O and OH /H2O. 21.7 Lewis Acids and Bases Practice Questions Do the practice problems associated with Section 3 Lewis Theory at the link below: http://staarhelper.com/Mr_B_Science/daily_lessons/cacid.htm Answers Answers are given on the web site. Review Questions 1. What is the difference between a Lewis acid or base and a Brønsted Lowry acid or base? 2. What is required to happen in Lewis acid-base reactions? 3. Do all Lewis acid-base reactions involve protons? Answers 5 1. The Lewis system looks at electron pairs while the Brønsted-Lowry approach focuses on proton exchange. 2. A covalent bond must be formed. 3. No. 21.8 Ion-Product of Water Practice Questions Read the material on the first two pages of the link below and do those practice problems: http://www.vigoschools.org/~mmc3/Chem%201/Lecture%20Notes/L2%20- %20Hydrogen%20Ions%20and%20pH%20-%2015.1.pdf Answers 9. a. basic, b. basic c. acidic d. neutral. 10. 1 x 10-11M, basic Review Questions 1. What is an acidic solution? 2. What is a basic solution? 3. What is the [OH-] of a solution which has a [H+] of 1 x 10-5M? Answers 1. Concentration of hydrogen ions is greater than the concentration of hydroxide ions. 2. Concentration of hydroxide ions is greater than the concentration of hydrogen ions. 3. [OH-] = 1 x 10-9M. 21.9 The pH Scale Practice Questions 6 Read the material at the link below and answer the following questions: http://staff.jccc.net/pdecell/chemistry/phscale.html 1. What is a buffer? 2. How much more acidic is vinegar than grapefruit? 3. How much more basic is soapy water than milk of magnesia? Answers 1. A solution that resists pH changes when acid or base or added. 2. Ten times more acidic. 3. One hundred times more basic. Review Questions 1. What is one value of using pH instead of molar concentrations? 2. Is coffee an acidic or a basic substance? 3. If a material has a pH of 9.3, is it acidic or basic? Answers 1. A simple number can be used instead of an exponential expression. 2. Acidic. 3. Basic. 21.10 Calculating pH of Acids and Bases Practice Questions Carry out the requested calculations at the link below: http://www.sciencegeek.net/APchemistry/APtaters/pHcalculations.htm Answers Answers are given at the web site. Review Questions 1. What is the pH of a 4.5 x 10-3 M HI solution? 7 2. What is the pH of a 3.67 x 10-5 M NaBr solution? 3. If we have a weak base with a low ionization constant, can we assume that the [OH-] in the solution is equal to the concentration of the base? Answers 1. pH = 2.4. 2. pH = 9.56. 3. No, the hydroxide ion concentration will not be equal to the molar concentration of the base because all the OH- will not be in the dissociated form. 21.11 The pOH Concept Practice Questions Do all calculations at the link below that involve pOH: http://www.sciencegeek.net/APchemistry/APtaters/pHcalculations.htm Answers Answers are provided on the web site. Review Questions 1. What is the formula for calculating pOH? 2. What pOH value is indicative of an acidic solution? 3. A pOH value of 3 would indicate what type of solution? Answers 1. pOH = -log[OH-] 2. A value of less than 7. 3. A basic solution. 21.12 Strong and Weak Acids and Acid Ionization Constant (Ka) Practice Questions 8 Read the material at the link below and answer the following questions: http://www.chemguide.co.uk/physical/acidbaseeqia/acids.html 1. Why is the [H2O] factor not included in the expression for Ka? 2. When we write H+, what are we really talking about? 3. Which is the weaker acid: methanoic or ethanoic acid? Answers 1. Because the concentration of the water is virtually constant. 2. Hydroxonium ions. 3. Ethanoic acid. Review Questions 1. Why is the chloride ion the weakest conjugate base? 2. What is the percent ionization in a 0.1 M solution of acetic acid? 3. Which is the stronger acid: HF or benzoic acid? Answers 1. It is incapable of accepting H+ ions. 2. 1.3%. 3. Hydrofluoric acid. 21.13 Strong and Weak Bases and Base Ionization Constant (Kb) Practice Questions Read the material at the link below and answer the following questions: http://www.chemguide.co.uk/physical/acidbaseeqia/bases.html 1. In the presence of hydroxide ions, which way does the equilibrium shift for the equation showing the dissociation of water? 2. What percentage of ammonia in solution actually produces hydroxide ions? 3. How does the position of equilibrium relate to the strength of a weak base? Answers 1. The equilibrium shifts toward the left side of the equation, according to the Le Chatelier’s Principle. 9 2. 1%. 3. The further the equilibrium is to the left, the weaker the base. Review Questions 1. Define a strong base. 2. Define a weak base. 3. Which is the stronger base: pyridine or urea? Answers 1.