Suggested Problems: p #58, 59, 65, 69, 74, 80, 85, 86, 90, 92, 93, 98, 99

Transcription

1 Chemistry I Accelerated Study Guideline - Chapter 19 Acids, Bases and Salts By the end of this unit, the skills you should be able to demonstrate are: 1. List properties of acids and bases. 2. Define and Give Examples of Arrhenius acids and bases. 3. Classify substances as acids or bases, and identify conjugate acidbase pairs in acid-base reactions, using the Brønstead-Lowry theory. 4. Classify substances as Lewis acids or bases. 5. Complete and balance a neutralization reaction. 6. Categorize acids and bases as strong or weak using K a and K b and give examples of each. 7. Derive and Use ionization constants. 8. Define acidic and basic anhydrides. Write formulas for them. 9. Write the equation for the self-ionization of water. 10. Classify a solution as neutral, acid or base given the hydrogen-ion or hydroxide ion concentration. 11. Calculate the ph or the poh of a solution given either the hydrogen or hydroxide ion concentration. 12. Describe the processes of hydrolysis and buffering. 13. Describe at least two methods used to measure ph. 14. State the principles and uses of indicators. 15. Explain the process of titration and perform calculations using the data from titrations. Suggested Problems: p #58, 59, 65, 69, 74, 80, 85, 86, 90, 92, 93, 98, 99

2 Chemistry Video: Acids, Bases and Salts 1. What do acids, bases and salts form in solution? 2. Why are acids, bases and salts called electrolytes? 3. How are nerve cells like a battery? 4. Litmus turns what color in acid? Base? 5. What does an acid do in solution? 6. What is H 3 O + called? 7. What is the general rule about oxides and acids and bases? 8. What is a more useful definition for acids and bases using the term proton? 9. What is the Lewis theory of acids and bases? 10. What does strong and weak refer to with acids and bases? 11. Can water molecules form ions by themselves? 12. What does ph stand for? 13. What ph is Acid? Neutral? Base? 14. What is a buffer? 15. How many buffers are in human blood? 16. What is a salt? page 2

3 Defining Acids and Bases On the line next to the item, write A if the statement is a property of an acidic solution. Write B if it is a property of a basic solution, and write X if it is a property of both acidic and basic solutions. 1. Often feels smooth and slippery 3. Stings in open wounds 5. has a bitter taste 7. is an electrolyte 9. turns litmus paper from red to blue Answer the following questions. 11. What is the Arrhenius definition of acids and bases? 2. has a sour taste 4. reacts vigorously with metals 6. turns litmus paper from blue to red 8. often looks like pure water 10. does not usually react with metals 12. What is the Brønsted-Lowery definition of acids and bases? 13. Why might ammonia not be considered a base according to the Arrhenius definition while the ammonium ion is considered an acid? 14. Why is the Brønsted-Lowery definition of acids and bases considered more encompassing than the Arrhenius definition? 15. Why are Brönsted-Lowery acids and bases sometimes called proton donors and acceptors? 16. What is the Lewis definition of acids and bases? Define each of the following: 17. Acidic Hydrogens 18. Binary Acids 19. Oxy acids 20. Carboxylic acid 21. Amines page 3

4 Name the following acids and bases 22. HNO H 3 PO HClO 25. KOH 26. H 2 SO H 2 CO HC 2 H 3 O CH 3 NH 2 Complete each of the following sentences by filling in the appropriate word or phrase from the list below. Word List amphoteric acid-base indicator conjugate electrolyte hydronium ion neutralization reaction salt 30. An ionic compound that forms from an acid-base neutralization reactions is a(n). 31. A(n) is a substance that conducts electricity when dissolved in water. 32. The formula H 3 O + represents a(n). 33. The reaction between an acid and a base is called a(n). 34. A(n) turns one color in an acidic solution and another color in a basic solution. 35. The chloride ion (Cl ) is the base of hydrochloric acid (HCl). Reviewing Acids and Bases Determine whether each of the following compounds contains an acidic hydrogen. Explain your answers 1. Nitric Acid 2. Hydrobromic acid 3. Methane 4. Hydrogen gas page 4

5 For the following reactions write the formula equation, place a single arrow (-->) between the reactants and the products if the reaction goes to completion. Place a double arrow (<-->) if the reaction reaches equilibrium. For each reaction label the acid (A), the base (B), the conjugate acid (CA), and the conjugate base (CB). 5. Nitrous Acid (aq) plus water (l) Hydronium (aq) and nitrite (aq) ions 6. Hydrocyanic Acid (aq) plus water (l) Hydronium (aq) and cyanide (aq) ions 7. Nitric acid (aq) plus water hydronium ion (aq) plus nitrate ion (aq) 8. Acetic acid (aq) plus water hydronium ion (aq) plus acetate ion (aq) 9. Ammonia (aq) plus water hydroxide ion(aq) plus ammonium ion(aq) 10. hydronium ion (aq) plus hydroxide ion (aq) water plus water Acid-Base Constant Practice Problems 1. Acetic acid is a weak acid. If the initial concentration of acetic acid is M and the equilibrium concentration of hydronium ion is.0019 M, calculate the K a for acetic acid. HA + H 2 O ---> A + H 3 O + >>>> K a = [A ][H 3 O + ]/[HA] For every one hydronium ion that forms, one conjugate base must also form so if those concentrations started equal they must end equal. Also for every hydronium ion and conjugate base that forms, one acid must have dissociated. Therefore, the starting concentration, M minus the amount that dissociated, M equals the final or equilibrium concentration of M Calculating K a = (0.0019)(0.0019)/ or (0.0019) 2 / = 1.82 x 10 5 or in sig. dig. 1.8 x 10 5 In most cases for weak acids the initial and the equilibrium concentrations are essentially the same. Does subtracting the amount dissociated make a difference? Let s compare and find out: Calculating K a = (0.0019) 2 /0.200 = x 10 5 or in sig. dig. 1.8 x 10 5 (no difference) 2. Ammonia is a weak base. If the initial concentration of ammonia is M and the equilibrium concentration of hydroxide ion is 1.6 x 10 3 M, calculate the K b for ammonia. page 5

6 3. Butylamine is a weak base. If the initial concentration of butylamine is M and the equilibrium concentration of hydroxide ion is 8.6 x 10 6 M, calculate the K b for butylamine. 4. Formic acid is a weak monoprotic acid made by ants. If the initial concentration of the formic acid is 0.10 M and the equilibrium concentration of hydronium ion is 4.2 x 10 3 M, calculate the K a for formic acid. 5. Isobutylamine is a weak base. If the initial concentration of isobutylamine is M and the equilibrium concentration of hydroxide ion is 4.0 x 10 3 M, calculate the K b for isobutylamine. 6. Gallic acid is a weak monoprotic acid. If the initial concentration of the gallic acid is M and the equilibrium concentration of hydronium ion is 3.3 x 10 3 M, calculate the K a for gallic acid. 7. Triethylamine is a weak base. If the initial concentration of triethylamine is M and the equilibrium concentration of hydroxide ion is 4.4 x 10 3 M, calculate the K b for triethylamine. 8. Dipropylamine is a weak base. If the initial concentration of dipropylamine is M and the equilibrium concentration of hydroxide ion is M, calculate the K b for dipropylamine. 9. Uric acid is a weak monoprotic acid made by ants. If the initial concentration of the uric acid is M and the equilibrium concentration of hydronium ion is 3.4 x 10 2 M, calculate the K a for uric acid. 10. Hydrocyanic acid is a weak monoprotic acid. If the initial concentration of the Hydrocyanic acid is M and the equilibrium concentration of hydronium ion is 4.8 x 10 2 M, calculate the K a for cyanic acid mol of a weak base is dissolved in water to a total volume of 1.5 L. At equilibrium the concentration of hydroxide ion is M, calculate the K b for this base. page 6

7 mol of a weak acid is dissolved in water to a total volume of 0.75 L. At equilibrium the concentration of hydronium ion is M, calculate the K a for this acid. Predict whether the final solution in each situation will be acidic, basic, neutral or if it is impossible to predict. In all cases you can assume equal concentrations of acid and base are used. 13. A strong acid reacts with a strong base A strong acid reacts with a weak base A weak acid reacts with a strong base A weak acid reacts with a weak base 16. Acid-Base Hydrolysis Hydrolysis occurs when certain salts dissolve in water to form solutions that have acidic or basic properties. A rule for predicting the properties of solutions of salts is based upon the concept of strong acids and strong bases in the Arrhenius sense. The rules are summarized in the table below: Salt formed from Water solution exhibits Example Strong acid + strong base no hydrolysis - neutral solutions KCl Strong acid + weak base hydrolysis to form acidic solution FeSO 4 Weak acid + strong base hydrolysis to form basic solution Na 2 CO 3 Weak acid + weak base Must use Ka and Kb to determine Pb(C 2 H 3 O 2 ) 2 The commonly used strong acids are hydrochloric, nitric and sulfuric. The commonly used strong bases are sodium hydroxide, potassium hydroxide, and calcium hydroxide. Predict the hydrolysis effect of each of the following salts. For each answer write acidic, basic neutral or need Ka and Kb. 1. Na 3 PO 4 2. Na 2 SO 4 3. NaC 2 H 3 O 2 4. NH 4 NO 3 5. NH 4 Cl 6. Fe 3 (PO 4 ) 2 7. Ca(NO 3 ) 2 8. KC 2 H 3 O 2 9. CuSO Al(NO 3 ) NaCl 12. K 2 CO 3 page 7

8 Any oxygen-containing substance that will produce an acid when dissolved in water is called an acid anhydride. Any oxygen-containing substance that will produce a base when dissolved in water is called an basic anhydride. Anhydride means without water. Metal oxides tend to form basic anhydrides and nonmetal oxides tend to form acidic anhydrides. Predict the acidic or basic nature of the following anhydrides: 13. CaO 14. NO 15. CO SO Na 2 O 18. Rb 2 O Complete and balance the following: 19. CaO + H 2 O > 20. CO 2 + H 2 O > 21. Na 2 O + H 2 O > 22. SO 3 + H 2 O > Determining the Strengths of Acids and Bases If the statement is true, write true. If it is false change the underlined word(s) to make the statement true. 1. A strong acid readily transfers H + ions to water to form hydronium ions. 2. Strong acids are weak electrolytes. 3. Substances that have the strongest affinity for hydrogen ions are strong bases. 4. Weak acids do not completely ionize in water. 5. The stronger an acid, the stronger its conjugate base. 6. Salts are weak electrolytes. Answer the following questions 7. What do acid and base dissociation constants measure? 8. What are salt-hydrolysis reactions? page 8

9 9. Why is spilling 1 M acetic acid relatively harmless compared to spilling 1 M hydrochloric acid? 10. Defend or refute this statement: Strong acids are strong electrolytes. 11. Describe the relative strength of acids and their conjugate bases. Bases and their conjugate acids. Kw/pH problems 1. What is the hydroxide ion concentration in saturated limewater if hydronium ion concentration = 3.98 x M? Is limewater acidic, basic, or neutral? 2. What is the [H 3 O + ] in a wheat flour and water solution if hydroxide ion concentration = 1.00 x 10 8 M? Is wheat flour and water acidic, basic, or neutral? 3. What is the hydronium ion concentration in 0.1 M ammonia if hydroxide ion concentration = 1.26 x 10 3 M? Is ammonia acidic, basic, or neutral? 4. What is the hydroxide ion concentration in butter if hydronium ion concentration = 6.00 x 10 7 M? Is butter acidic, basic, or neutral? 5. During the course of the day, human saliva varies between acidic and basic. What is the hydronium ion concentration in saliva if hydroxide ion concentration = 3.16 x 10 8 M? Is this sample of saliva acidic, basic, or neutral? 6. What is the [H 3 O + ] in peaches if hydroxide ion concentration = 3.16 x M? Are peaches acidic, basic, or neutral? page 9

10 7. What is the hydroxide ion concentration in 0.1 M bicarbonate of soda if hydronium ion concentration = 3.98 x 10 9 M? Is bicarbonate of soda acidic, basic, or neutral? 8. A sample of human blood is found to have a hydronium ion concentration = 3.72 x 10 8 M? What is the ph of this sample? Is it acidic, basic, or neutral? 9. Analysis of samples of maple syrup reveals that the hydroxide ion concentration = 5.00 x 10 8 M. What is the ph of this syrup? Is it acidic, basic, or neutral? 10. In a sample of bananas and water it was found that the hydronium ion concentration = 2.51 x 10 5 M. What is the ph of this sample? Is it acidic, basic, or neutral? 11. A soft drink was found to have a hydroxide ion concentration = 4.11 x 10 9 M? What is the ph of this soft drink? Is it acidic, basic, or neutral? 12. Tomatoes are found to have a hydronium ion concentration = 6.20 x 10 5 M? What is the ph of these tomatoes? Are they acidic, basic, or neutral? 13. A sample of urine is found to have a hydronium ion concentration = 6.30 x 10 6 M? What is the ph of this sample? Is it acidic, basic, or neutral? 14. In sour pickles the hydroxide ion concentration = 1.60 x M. What is the ph of the pickles? Are they acidic, basic, or neutral? page 10

11 The self-ionization of Water and ph Matching - On the line at the left, write the letter of the definition that best matches each term. 1. self-ionization 2. pure water a. has H 3 O + concentration greater than 1 x 10 7 M b. has H 3 O + and OH concentrations of 1 x 10 7 M 3. ion-product constant c. has ph greater than 7 4. ph scale d. describes this reaction: H 2 O + H 2 O <-----> H 3 O + + OH 5. acidic solution e. has ph = 7; may contain ions other than H 3 O + + OH 6. basic solution f. is equal to 1 x at 25 C 7. neutral solution g. describes acidity or basicity of a solution 8. In pure water, what is the concentration of H 3 O + + OH ions? What is the ph? 9. The ph of a solution decreases from 9 to 7. How does the [H 3 O + ] change? By what factor? True or False - If the statement is true, write true. It is false, change the underlined word or words to make the statement true. 10. In the reaction H 2 O + H 2 O <-----> H 3 O + + OH, products are favored. 11. The ion product constant applies to every water solution at a given temperature. 12. An acidic solution contains only H 3 O + ions. 13. A solution with a ph of 4 is acidic. 14. A buffer is usually made up of a weak acid or base and its salt. 15. An increase in the concentration of a buffer decreases the buffer capacity. 16. The ph of a solution remains constant in the presence of a buffer if acid or a base is added beyond the buffer capacity. 17. Adding OH ions beyond the buffer capacity causes a decrease in the ph. 18. All buffers have a limited capacity to neutralize H 3 O + + OH ions. 19. Indicators are made from neutral solutions. In each of the following situations, determine if the ph is decreased, increased or remains constant. 20. Acid is added to a buffered solution until the buffer capacity is surpassed. 21. Base is added to a buffered solution, not exceeding the buffer capacity. 22. Base is added to a buffered solution, until the buffer capacity is surpassed. 23. Acid is added to a buffered solution, not exceeding the buffer capacity. page 11

12 24. What is the function of a buffer in blood? Why is it so important? 25. How can large changes in ph levels affect reactions? 26. What happens at the molecular level when an acid is added to a buffer solution? What about a base? 27. An acid is added to a buffer solution of acetic acid and its conjugate base. Write the equation for the reaction that occurs. 28. A base is added to a buffer solution of ammonia and its conjugate acid. Write the equation for the reaction that occurs Titration Practice Problems 1. A volume of 30.0 ml of 0.25 M hydrochloric acid neutralizes a 50.0 ml sample of potassium hydroxide. What is the concentration of the potassium hydroxide? 2. A volume of 46.0 ml of 0.40 M sodium hydroxide neutralizes an 80.0 ml sample of hydrocyanic acid. What is the concentration of the hydrocyanic acid? 3. A volume of 90.0 ml of 0.20 M hydrobromric acid neutralizes a 60.0 ml sample of sodium hydroxide. What is the concentration of the sodium hydroxide? page 12

13 4. A volume of 50.0 ml of 0.30 M hydrochloric acid neutralizes a 60.0 ml sample of calcium hydroxide. What is the concentration of the calcium hydroxide? 5. A volume of 20.0 ml of 0.25 M Aluminum hydroxide neutralizes a 75.0 ml sample of sulfuric acid. What is the concentration of the sulfuric acid? 6. A volume of ml of 0.40 M hydrosulfuric acid neutralizes a 90.0 ml sample of aluminum hydroxide. What is the concentration of the aluminum hydroxide? 7. A mass of 2.91 g of hydrobromric acid neutralizes a 80.0 ml sample of calcium hydroxide. What is the concentration of the calcium hydroxide? 8. A total of 4.51 x formula units of sodium hydroxide neutralizes a 30.0 ml sample of phosphorous acid. What is the concentration of the phosphorous acid? Acids - Bases Titration acid-base titration end point equivalence point indicator phenolphthalein standard solution titration curve 1. The point at which exactly enough standard solution is added to neutralize the unknown solution is the. 2. A(n) is used to represent ph data. 3. A(n) is a carefully controlled neutralization reaction. 4. A(n) changes color at certain ph values. 5. A(n) contains an acid or a base in known concentration. 6. A common indicator used in titrations is. 7. The point at which the indicator changes color is the of the reaction. page 13

14 8. Why is it difficult to directly measure the concentration of a weak acid such as acetic acid? 9. How is an indicator useful in a titration? 10. Why should the end point of a titration be close to the equivalence point. Acids and Bases - Review Activity acid acid-base neutralization acid-base titration acidic solution amphoteric substance base basic solution Brönsted-Lowry definition buffer conjugate pair dissociation end point equivalence point hydrogen ion hydrolysis hydronium ion hydroxide ion ion product ionization ionization constant indicator logarithm neutral solution neutralization nonelectrolyte ph proton acceptor proton donor salt self ionization standard solution strong conjugate acid strong conjugate base strong electrolyte weak conjugate acid weak conjugate base weak electrolyte A substance whose water solution does not conduct an electric current is called a(n). A substance whose water solution is a poor conductor is a (n). One whose solution is a good conductor is a(n). The ability to conduct an electric current can result from, the action of water on ionic solids to produce and dispense hydrated ions. The ability to conduct can also result from, the formation of charged particles by means of the reaction between water molecules and molecular substances. According to Arrhenius, a(n) is a substance that, when mixed with water, produces the positively charged. This charged particle is hydrated by a water molecule, producing a(n). The equilibrium constant for the formation of charged particles by an acid is called a(n) of the acid. According to the, an acid is a(n) and a base is a(n). A substance that can act as either is called a(n). An acid-base pair in which the acid and base are on opposite sides of an equation and are related by the transfer of a proton is called a(n). A strong acid has a(n), and a weak acid has a(n). page 14

15 Salts of weak acids or weak bases can react with water in a process called. Water molecules can react with one another to produce charged particles in a process called. The quantity K w, which is the for water, gives information on the concentration of these particles. The negative of the hydrogen-ion concentration is called the. The value of this quantity is greater than 7 in a(n). Its value equals 7 in a(n), and is less than 7 in a(n). A(n) is a mixture of a acid and a or a base and a that causes a solution to resist changes in its hydrogen-ion concentration. A(n) is a substance that changes color over a narrow range of hydrogen-ion concentrations. Hydrogen ions combine with hydroxide ions during a reaction called. A laboratory procedure that makes use of this reaction is called a(n). This procedure makes use of a solution of known concentration, called a(n). When enough of this solution has been added to react completely with the solution of unknown concentration, the has been reached. Acid/Base - Challenge Problems 1. What is the effect of dissolving potassium sulfite in a M solution of sulfuric acid? Would you expect the acidity to increase or decrease? Describe a mechanism that explains your answer. 2. What is the ph of a saturated solution Iron(III) hydroxide? K sp = 3.98 x page 15

16 3. What is the ph of a M solution of Acetic Acid? K a = 1.75 x What is the ph of a M solution of the base diammine? K b = 8.71 x 10 7 page 16

17 5. What is the ph of a M solution of Phosphoric Acid? K a (H 3 PO 4 ) = 7.08 x K a (H 2 PO 4 ) = 6.31 x K a (HPO 4 2 ) = 4.17 x You are titrating a 50.0 ml sample of hydrochloric acid with M potassium hydroxide. After you have already added 42.3 ml of the potassium hydroxide you realize that you forgot to add the phenolphthalein indicator. When you add the indicator, the solution turns bright pink indicating that you have already missed the end point. You decide to back-titrate by adding M nitric acid. The solution turns colorless after an addition of 10.1 ml of the nitric acid. What is the concentration of the original solution of hydrochloric acid. page 17

18 7. What is the final ph of a solution that is made with acetic acid and of Copper(II) hydroxide in ml of solution in each of the following two situations. K a acetic acid = 1.75 x 10 5 K sp Copper(II) hydroxide = 2.19 x a g of each solid b g of acid and g base page 18

19 Acid-Base Crossword ACROSS DOWN 1. Number for which a given logarithm stands 2. Analytical method involving neutralization 3. One more oxygen 3. Acid that can donate more than one proton 6. Hydroxide ion formula 4. Describes a solution for which ph = 7 7. Scale for ranking hydronium ion concentrations 5. Naturally occurring acid in ants 8. Taste of bases 7. Commonly used indicator 9. Hydrated proton 8. Symbol for element 5 11 Hydrochloric acid formula 9. Ion released by many bases 13. Describes an acid containing one reacting hydrogen atom. 10. Loss of electrons 12. Common name for calcium oxide 14. Contains x particles 16. Describes a strongly irritating basic substance 15. Weak acid or base whose color depends on hydronium ion concentration 18. A scientist who proposed an acid-base theory 17. Sodium hydroxide formula 19. Has formula NH Symbol for element Acid with formula HC 2 H 3 O Describes species that are related by a difference in protons 23. Mineral containing metal 24. Acid found in fruits 25. Scientist who created electron dot structures 26. Has ph less than Charged atom 28. Symbol for element Acid with formula HNO 3 page 19

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