Chapter 15. Preview. Lesson Starter Objectives Hydronium Ions and Hydroxide Ions The ph Scale Calculations Involving ph

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1 Preview Lesson Starter Objectives Hydronium Ions and Hydroxide Ions The ph Scale Calculations Involving ph

2 Section 1 Aqueous Solutions and the Concept of ph Lesson Starter Describe what is taking place during the selfionization of water.

3 Section 1 Aqueous Solutions and the Concept of ph Objectives Describe the self-ionization of water. Define ph, and give the ph of a neutral solution at 25 C. Explain and use the ph scale. Given [H 3 O + ] or [OH ], find ph. Given ph, find [H3O + ] or [OH ].

4 Section 1 Aqueous Solutions and the Concept of ph Hydronium Ions and Hydroxide Ions Self-Ionization of Water In the self-ionization of water, two water molecules produce a hydronium ion and a hydroxide ion by transfer of a proton. HO() 2 l + HO() 2 l HO( 3 aq ) + OH( aq) In water at 25 C, [H 3 O + ] = M and [OH ] = M. The ionization constant of water, K w, is expressed by the following equation. K w = [H 3 O + ][OH ]

5 Section 1 Aqueous Solutions and the Concept of ph Hydronium Ions and Hydroxide Ions, continued Self-Ionization of Water, continued At 25 C, K w = [H 3 O + ][OH ] = ( )( ) = K w increases as temperature increases

6 Section 1 Aqueous Solutions and the Concept of ph Hydronium Ions and Hydroxide Ions, continued Neutral, Acidic, and Basic Solutions Solutions in which [H 3 O + ] = [OH ] is neutral. Solutions in which the [H 3 O + ] > [OH ] are acidic. [H 3 O + ] > M Solutions in which the [OH ] > [H 3 O + ] are basic. [OH ] > M

7 Section 1 Aqueous Solutions and the Concept of ph Hydronium Ions and Hydroxide Ions, continued Calculating [H 3 O + ] and [OH ] Strong acids and bases are considered completely ionized or dissociated in weak aqueous solutions. s HO 2 NaOH( ) Na ( aq ) + OH ( aq) 1 mol 1 mol 1 mol M NaOH solution has an [OH ] of M The [H 3 O + ] of this solution is calculated using K w. K w = [H 3 O + ][OH ] = [OH ] [H3 O ] M -2

8 Section 1 Aqueous Solutions and the Concept of ph Hydronium Ions and Hydroxide Ions, continued Calculating [H 3 O + ] and [OH ] If the [H 3 O + ] of a solution is known, the [OH ] can be calculated using K w. [HCl] = M [H 3 O + ] = M K w = [H 3 O + ][OH ] = [OH ] M [H3O ]

9 Section 1 Aqueous Solutions and the Concept of ph Some Strong Acids and Some Weak Acids

10 Section 1 Aqueous Solutions and the Concept of ph Concentrations and K w

11 Section 1 Aqueous Solutions and the Concept of ph Hydronium Ions and Hydroxide Ions, continued Calculating [H 3 O + ] and [OH ] Sample Problem A A M solution of HNO 3 has been prepared for a laboratory experiment. a. Calculate the [H 3 O + ] of this solution. b. Calculate the [OH ].

12 Section 1 Aqueous Solutions and the Concept of ph Hydronium Ions and Hydroxide Ions, continued Calculating [H 3 O + ] and [OH ], continued Sample Problem A Solution Given: Concentration of the solution = M HNO 3 Unknown: a. [H 3 O + ] b. [OH ] Solution: HNO a. 3 is a strong acid HNO ( l ) + H O( l ) H O ( aq ) + NO ( aq) mol 1 mol 1 mol 1 mol molarity of HNO 3 mol HNO 3 1L solution

13 Section 1 Aqueous Solutions and the Concept of ph Hydronium Ions and Hydroxide Ions, continued Calculating [H 3 O + ] and [OH ], continued Sample Problem A Solution, continued a. mol HNO3 1 mol H3O mol H3O L solution 1 mol HNO L solution 3 molarity of H O 3 b. [H 3 O + ][OH ] = [OH ] [H O ] 3 14

14 Section 1 Aqueous Solutions and the Concept of ph Hydronium Ions and Hydroxide Ions, continued Calculating [H 3 O + ] and [OH ], continued Sample Problem A Solution, continued a mol HNO3 1 mol H3O 1L solution 1molHNO mol H3O 4 1L solution M H O 3 3 b. [OH ] [H O ] M

15 Section 1 Aqueous Solutions and the Concept of ph The ph Scale The ph of a solution is defined as the negative of the common logarithm of the hydronium ion concentration, [H 3 O + ]. ph = log [H 3 O + ] example: a neutral solution has a [H 3 O + ] = The logarithm of is 7.0. ph = log [H 3 O + ] = log( ) = ( 7.0) = 7.0

16 Section 1 Aqueous Solutions and the Concept of ph ph Values as Specified [H3O+]

17 Section 1 Aqueous Solutions and the Concept of ph The ph Scale The poh of a solution is defined as the negative of the common logarithm of the hydroxide ion concentration, [OH ]. poh = log [OH ] example: a neutral solution has a [OH ] = The ph = 7.0. The negative logarithm of K w at 25 C is ph + poh = 14.0

18 Section 1 Aqueous Solutions and the Concept of ph poh Click below to watch the Visual Concept. Visual Concept

19 Section 1 Aqueous Solutions and the Concept of ph The ph Scale

20 Section 1 Aqueous Solutions and the Concept of ph Approximate ph Range of Common Materials

21 Section 1 Aqueous Solutions and the Concept of ph [H3O+], [OH ], ph and poh of Solutions

22 Section 1 Aqueous Solutions and the Concept of ph Comparing ph and poh Click below to watch the Visual Concept. Visual Concept

23 Section 1 Aqueous Solutions and the Concept of ph Calculations Involving ph There must be as many significant figures to the right of the decimal as there are in the number whose logarithm was found. example: [H 3 O + ] = one significant figure ph = 7.0

24 Section 1 Aqueous Solutions and the Concept of ph Using Logarithms in ph Calculations

25 Section 1 Aqueous Solutions and the Concept of ph Calculations Involving ph, continued Calculating ph from [H 3 O + ], continued Sample Problem B What is the ph of a M NaOH solution?

26 Section 1 Aqueous Solutions and the Concept of ph Calculations Involving ph, continued Calculating ph from [H 3 O + ], continued Sample Problem B Solution Given: Identity and concentration of solution = M NaOH Unknown: ph of solution Solution: concentration of base concentration of OH concentration of H 3 O + ph [H 3 O + ][OH ] = [OH ] [H3 O ] M -3 ph = log [H 3 O + ] = log( ) = 11.00

27 Section 1 Aqueous Solutions and the Concept of ph Calculations Involving ph, continued Calculating ph from [H 3 O + ], continued ph = log [H 3 O + ] log [H 3 O + ] = ph [H 3 O+] = antilog ( ph) [H 3 O + ] = 10 ph The simplest cases are those in which ph values are integers.

28 Section 1 Aqueous Solutions and the Concept of ph Calculations Involving ph, continued Calculating [H 3 O + ] and [OH ] from ph, continued Sample Problem D Determine the hydronium ion concentration of an aqueous solution that has a ph of 4.0.

29 Section 1 Aqueous Solutions and the Concept of ph Calculations Involving ph, continued Calculating [H 3 O + ] and [OH ] from ph, continued Sample Problem D Solution Given: ph = 4.0 Unknown: [H 3 O + ] Solution: [H 3 O + ] = 10 ph [H 3 O + ] = M

Section 1 Aqueous Solutions and the Concept of ph Calculations Involving ph, continued ph Calculations and the Strength of Acids and Bases The ph of

30 Section 1 Aqueous Solutions and the Concept of ph Calculations Involving ph, continued ph Calculations and the Strength of Acids and Bases The ph of solutions of weak acids and weak bases must be measured experimentally. The [H 3 O + ] and [OH ] can then be calculated from the measured ph values.

31 Section 1 Aqueous Solutions and the Concept of ph ph of Strong and Weak Acids and Bases

32 Section 1 Aqueous Solutions and the Concept of ph ph Values of Some Common Materials

33 Section 2 Determining ph and Titrations Preview Objectives Indicators and ph Meters Titration Molarity and Titration

34 Section 2 Determining ph and Titrations Objectives Describe how an acid-base indicator functions. Explain how to carry out an acid-base titration. Calculate the molarity of a solution from titration data.

35 Section 2 Determining ph and Titrations Indicators and ph Meters Acid-base indicators are compounds whose colors are sensitive to ph. Indicators change colors because they are either weak acids or weak bases. H In H + In HIn and In are different colors. In acidic solutions, most of the indicator is HIn In basic solutions, most of the indicator is In

36 Section 2 Determining ph and Titrations Indicators and ph Meters The ph range over which an indicator changes color is called its transition interval. Indicators that change color at ph lower than 7 are stronger acids than the other types of indicators. They tend to ionize more than the others. Indicators that undergo transition in the higher ph range are weaker acids.

37 Section 2 Determining ph and Titrations Indicators and ph Meters A ph meter determines the ph of a solution by measuring the voltage between the two electrodes that are placed in the solution. The voltage changes as the hydronium ion concentration in the solution changes. Measures ph more precisely than indicators

38 Section 2 Determining ph and Titrations Color Ranges of Indicators

39 Section 2 Determining ph and Titrations Color Ranges of Indicators

40 Section 2 Determining ph and Titrations Color Ranges of Indicators

41 Section 2 Determining ph and Titrations Titration Neutralization occurs when hydronium ions and hydroxide ions are supplied in equal numbers by reactants. H 3 O + (aq) + OH (aq) 2H 2 O(l) Titration is the controlled addition and measurement of the amount of a solution of known concentration required to react completely with a measured amount of a solution of unknown concentration.

42 Section 2 Determining ph and Titrations Titration, continued Equivalence Point The point at which the two solutions used in a titration are present in chemically equivalent amounts is the equivalence point. The point in a titration at which an indicator changes color is called the end point of the indicator.

43 Section 2 Determining ph and Titrations Titration, continued Equivalence Point, continued Indicators that undergo transition at about ph 7 are used to determine the equivalence point of strongacid/strong base titrations. The neutralization of strong acids with strong bases produces a salt solution with a ph of 7.

44 Section 2 Determining ph and Titrations Titration, continued Equivalence Point, continued Indicators that change color at ph lower than 7 are used to determine the equivalence point of strongacid/weak-base titrations. The equivalence point of a strong-acid/weak-base titration is acidic.

45 Section 2 Determining ph and Titrations Titration, continued Equivalence Point, continued Indicators that change color at ph higher than 7 are used to determine the equivalence point of weakacid/strong-base titrations. The equivalence point of a weak-acid/strong-base titration is basic.

46 Section 2 Determining ph and Titrations Titration Curve for a Strong Acid and a Strong Base

47 Section 2 Determining ph and Titrations Titration Curve for a Weak Acid and a Strong Base

48 Section 2 Determining ph and Titrations Molarity and Titration The solution that contains the precisely known concentration of a solute is known as a standard solution. A primary standard is a highly purified solid compound used to check the concentration of the known solution in a titration The standard solution can be used to determine the molarity of another solution by titration.

49 Section 2 Determining ph and Titrations Performing a Titration, Part 1

50 Section 2 Determining ph and Titrations Performing a Titration, Part 1

51 Section 2 Determining ph and Titrations Performing a Titration, Part 1

52 Section 2 Determining ph and Titrations Performing a Titration, Part 2

53 Section 2 Determining ph and Titrations Performing a Titration, Part 2

54 Section 2 Determining ph and Titrations Performing a Titration, Part 2

55 Section 2 Determining ph and Titrations Molarity and Titration, continued To determine the molarity of an acidic solution, 10 ml HCl, by titration 1. Titrate acid with a standard base solution ml of M NaOH was titrated 2. Write the balanced neutralization reaction equation. HCl(aq) + NaOH(aq) NaCl(aq) + H 2 O(l) 1 mol 1 mol 1 mol 1 mol 3. Determine the chemically equivalent amounts of HCl and NaOH.

56 Section 2 Determining ph and Titrations Molarity and Titration, continued 4. Calculate the number of moles of NaOH used in the titration ml of M NaOH is needed to reach the end point mol NaOH 1 L 1 L 1000 ml mol HCl 1000 ml 10.0 ml 1 L ml mol NaOH used 5. amount of HCl = mol NaOH = mol 6. Calculate the molarity of the HCl solution M HCl

57 Section 2 Determining ph and Titrations Molarity and Titration, continued 1. Start with the balanced equation for the neutralization reaction, and determine the chemically equivalent amounts of the acid and base. 2. Determine the moles of acid (or base) from the known solution used during the titration. 3. Determine the moles of solute of the unknown solution used during the titration. 4. Determine the molarity of the unknown solution.

58 Section 2 Determining ph and Titrations Molarity and Titration, continued Sample Problem F In a titration, 27.4 ml of M Ba(OH) 2 is added to a 20.0 ml sample of HCl solution of unknown concentration until the equivalence point is reached. What is the molarity of the acid solution?

59 Section 2 Determining ph and Titrations Molarity and Titration, continued Sample Problem F Solution Given: volume and concentration of known solution = 27.4 ml of M Ba(OH) 2 Unknown: molarity of acid solution Solution: 1. balanced neutralization equation chemically equivalent amounts Ba(OH) 2 + 2HCl BaCl 2 + 2H 2 O 1 mol 2 mol 1 mol 2 mol

60 Section 2 Determining ph and Titrations Molarity and Titration, continued Sample Problem F Solution, continued 2. volume of known basic solution used (ml) amount of base used (mol) mol Ba(OH) 2 1L ml of Ba(OH) solution mol Ba(OH) 1 L 1000 ml mole ratio, moles of base used moles of acid used from unknown solution 2molHCl mol of Ba(OH) 2 in known solution mol Ba(OH) mol HCl

61 Section 2 Determining ph and Titrations Molarity and Titration, continued Sample Problem F Solution, continued 4. volume of unknown, moles of solute in unknown molarity of unknown amount of solute in unknown solution (mol) volume of unknown solution (ml) 1000 ml 1 L molarity of unknown solution

62 Section 2 Determining ph and Titrations Molarity and Titration, continued Sample Problem F Solution, continued 1. 1 mol Ba(OH) 2 for every 2 mol HCl mol Ba(OH) 1L 2molHCl 1molBa(OH) ml of Ba(OH) solution 1L 1000 ml mol Ba(OH) mol of Ba(OH) mol HCl 2

63 Section 2 Determining ph and Titrations Molarity and Titration, continued Sample Problem F Solution, continued mol HCl 1000 ml ml 1L -2 M HCl

64 End of Chapter 15 Show

ACID-BASE TITRATION AND PH

ACID-BASE TITRATION AND PH Section 1 Aqueous Solutions and the Concept of ph Hydronium and Hydroxide Ions Acids and bases form hydroxide and hydronium ions These ions are not the only ones in an aqueous