Intermediate Answer Key Chapter 21: Acids and Bases

CK-12 Chemistry Concepts - Intermediate Answer Key

Chapter 21: Acids and 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. Pink

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

Read the material at the site below and answer the following questions:

1 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

Questions

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. 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.

21.5 Brønsted-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 Brønsted-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

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

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

1. Problem 9: a. basic, b. basic c. acidic d. neutral. 2. Problem 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

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? 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.

21.10 Calculating pH of Acids and Bases

Practice

Questions

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 sued instead of an exponential expression. 2. Acidic. 3. Basic.

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

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. The concentration of water is very large and it is a constant. + 2. The hydronium ion H3O . 3. Ethanoic – it has a lower Ks.

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 has the lowest tendency to re-form HCl. 2. About 1.3% ionized? 3. HF – it has a larger Ka.

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. To the left. 2. About 1%. 3. The further to the left the equilibrium is, 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. One that ionizes completely in water. 2. One that does not ionize completely in water. 3. Pyridine – its Kb is much larger than that of urea.

21.14 Calculating Ka and Kb

Practice

Questions

Read the material at the link below and answer the following questions: http://www.ausetute.com.au/kb.html 1. What does an Arrhenius base dissociate to? 2. What does a Brønsted-Lowry base form in water? 3. How is percent ionization determined?

Answers

1. The cation of the base plus OH-. 2. The base reacts with water. The products are the protonated base plus a hydroxide ion. 3. % dissociation (ionization) = [OH- at equilibrium] ÷ [base initial] x 100.

Review

Questions

1. What approach is used for calculation of ionization constants? 2. What initial assumptions are made? 3. What equilibrium assumptions are made?

Answers

1. The ICE approach. 2. The concentrations of H+ and base anion are zero. 3. The concentrations of H+ and base anion are equal.

21.15 Calculating pH of Weak Acid and Base Solutions

Practice

Questions

Perform the calculations at the site below: http://www.sciencegeek.net/APchemistry/APtaters/pHcalculations.htm

Answers

Answers are given on the web site.

Review

Questions

1. What does x stand for in the equation? 2. What simplifying assumption is made? 3. What would x stand for if we were calculating pOH?

Answers

1. The hydrogen ion concentration. 2. The extent of ionization of a weak acid is small and x in the denominator can be ignored. 3. Concentration of the hydroxide ion.

21.16 Neutralization Reaction and Net Ionic Equations for Neutralization Reactions

Practice

Questions

Do the problems on the sheet at the link below: http://www.bbc.co.uk/bitesize/standard/chemistry/acids/reactions/revision/4/

Answers

Answers are on the web site.

Review

Questions

1. What is a neutralization reaction?

2. What is a salt? 3. Write the net ionic equation for the neutralization of a strong acid and a strong base.

Answers

1. Acid + base → salt + water. 2. An ionic compound composed of a cation from a base and an anion from an acid. 3. H+(aq) + OH-(aq)

21.17 Titration Experiment

Practice

Questions

Watch the video at the link below and answer the following questions: http://www.youtube.com/watch?v=g8jdCWC10vQ 1. What is the indicator used? 2. What color is it in acid solution? 3. What is the glass tube called that contains the known concentration of sodium hydroxide? 4. What other method can be used to determine the end-point of the titration?

Answers

1. Phenolphthalein. 2. Colorless. 3. A buret (sometimes spelled burette). 4. A pH meter.

Review

Questions

1. What is the standard solution? 2. How do you know you have reached the end-point? 3. What is the reaction that occurs during a titration?

Answers

1. A known concentration of sodium hydroxide. 2. The phenolphthalein turns pink. 3. A neutralization reaction: acid + base → salt + water.

21.18 Titration Calculations

Practice

Questions

Do the problems at the link below: http://www.sophia.org/acidbase-titration-calculations-concept

Answers

Answers are given on the web site.

Review

Questions

1. What assumption is made about the amounts of materials at the neutral point? 2. What is different about the calculation using sulfuric acid? 3. Why is the mole ratio important?

Answers

1. The moles of acid equal the moles of base. 2. There are two protons to neutralize in a molecule of sulfuric acid. 3. We need to know how many moles of acid are involved in the reaction.

21.19 Titration Curves

Practice

Questions

Read the material at the link below and answer the following questions: http://www.chemguide.co.uk/physical/acidbaseeqia/phcurves.html 1. Why is the equivalence point less than pH 7 for the titration of ammonia with HCl? 2. Why is it difficult to do a titration of a weak acid and a weak base? 3. Why do we get two inflection points for the titration of ethanedioic acid?

Answers

1. Some of the product formed is ammonium chloride, which can dissociate into ammonia and a proton.

2. There is no steep break in the curve to indicate where the equivalence point is. 3. There are two different acid dissociation constants.

Review

Questions

1. What does a titration curve tell us? 2. At what pH are the moles of acid and base equal? 3. Is the equivalence point for a weak acid-strong base titration the same as for a strong-acid-strong base titration?

Answers

1. The change in pH as base is added. 2. pH 7. 3. No, the pH is greater than 7.

21.20 Indicators

Practice

Questions

Watch the video at the link below and answer the following questions: http://www.youtube.com/watch?v=6Y4Y-__ME60 1. What was the acid used. 2. What was the base used? 3. What color was methyl orange in acid? in base? 4. What color did indigo carmine turn in acid? in base?

Answers

1. HCl. 2. NaOH. 3. Reddish-orange, yellow. 4. Dark blue, yellow.

Review

Questions

1. What is an indicator? 2. What would be the best indicator to use around pH 1? 3. What indicator besides phenolphthalein might you use for a pH 7 experiment?

Answers

1. A substance that turns different colors in acid or base solutions. 2. Methyl violet. 3. Phenol red.

21.21 Hydrolysis of Salts: Equations

Practice

Questions

Do problems 1, 2, 3, and 5 at the link below: http://chemwiki.ucdavis.edu/Physical_Chemistry/Physical_Properties_of_Matter/Solubilt y/Hydrolysis%3A_With_Respect_to_Acids,_Bases,_and_Salt_Solutions

Answers

Answers are given on the web site.

Review

Questions

1. How does F- produce a basic solution? 2. How does the ammonium ion produce an acidic solution? 3. Why does dissolved NaCl produce a neutral solution?

Answers

1. It reacts somewhat with water to form HF and OH-. 2. It releases a proton when it forms ammonia. 3. There are no acid-base equilibrium reactions occurring.

21.22 Calculating pH of Salt Solutions

Practice

Questions

Work the problems at the link below: http://www.sparknotes.com/chemistry/acidsbases/phcalc/problems.html

Answers

Answers are on the web site.

Review

Questions

1. In the first example, how do we know that we can ignore x when determining [F- ]? 2. In example two, how do we know the ammonium ion concentration? + + 3. Could we write the equilibrium in example two as NH4 → H + NH3?

Answers

1. The Kb is very small. 2. Ammonium chloride dissociated completely in water. 3. Yes, this equation is functionally equivalent to the more complete one.

21.23 Buffers

Practice

Questions

Read the material at the link below and answer the following questions: http://chemcollective.org/activities/tutorials/buffers/buffers3 1. What is a weak acid? 2. What does a conjugate base rarely do? 3. Write the generic equation for neutralization of a base by a weak acid. 4. Write the generic equation for neutralization of an acid by a weak base.

Answers

1. One that rarely loses a proton to water. 2. It rarely steals a proton from water. - - 3. OH + HA → A + H2O. 4. HCl + A- → HA + Cl-.

Review

Questions

1. What is a buffer? 2. How would the acetic acid/ acetate buffer system neutralize added base?

3. If acid is added to the carbonic acid/ carbonate buffer system, how is it neutralized?

Answers

1. A solution of a weak acid or base and its salt. 2. Some acetic acid would release protons to neutralize the base. 3. The carbonate anion would react with the excess acid.