Chap 17 No Titrate Calc No Clicker(2)

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    Chapter 17:

    Additional AqueousEquilibria

    Chemistry the Central Science,12thed

    Dr. Stacey Gulde

    1

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    Common-Ion Effect Common ion effectshiftin equilibrium caused

    by adding anion involvedin the equilibrium

    AKA Le ChteliersPrinciple

    If add NaC2H3O2, what happens?

    C2H3O2-causes equilibriumto shift Thus, [H+]decrease& pH becomes morebasic

    Dissociationof a weakelectrolyte (ie. HC2H3O2) decreaseswhen a strongelectrolyte (ie. NaC

    2

    H3

    O2

    ) containing acommon ion (ie. C2H3O2

    -) is added2

    )()((aq) 232232 aqOHCaqHOHHC

    C2H3O2-Na+

    breaks up into ions

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    Sample Problems1. Calculate the pH of a 0.50M HF solution.

    3

    )(aqHFI

    C

    E

    0.50M 0 0

    xx-x

    0.50x xx

    4108.6 x]50.0[

    ]][[

    x

    xxKa

    ]50.0[

    ][

    108.6

    24 x

    x

    Mx 018.0 ][

    H

    100]50.0[

    ]018.0[% xI %6.3% I

    (Assumption OK)

    ]018.0log[pH

    74.1pH

    Check 5% Rule:

    Appendix D

    Ignore x

    (W. Acid)

    )()( aqFaqH

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    Sample Problems2. Calculate the pH of a 0.50M HF solution when 0.10M

    NaF is added.

    4

    4108.6 x]50.0[]10.0][[

    xxxKa

    ]50.0[

    ]10.0][[108.6 4

    xx

    Mx 0034.0 ][

    H

    100]50.0[

    ]0034.0[% xI

    %68.0% I

    ]0034.0log[pH

    47.2pH

    More basic

    )()()( aqFaqHaqHF

    I

    C

    E

    0.50M 0 0.10M

    xx-x

    0.50x 0.10+xx

    Ignore x

    (W. Acid)

    (Common

    Ion)

    [HF] only:pH=1.74

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    Buffer

    Solutions Buffersweakacid/base & conjugateacid/base (salt)

    Should have similarconcentrations

    Sample Prob. #2: 0.50M HF with 0.10M NaF

    Naturalbuffers:

    Human blood maintains pH of 7.4

    Seawatermaintains pH of 8.1-8.3

    CalculatingpH of a buffer:

    Previous sample problem #2 (pH=2.47)

    OR use Henderson-Hasselbalch eq. (H-H eq)

    5

    )()()( aqFaqHaqHF (W. Acid) (CB)

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    Henderson-Hasselbalch Eq

    Sample Problem #2 Revisited: Calculate pH of a0.50M HF solution when 0.10M NaF is added.

    6

    acidbase

    pKpH a log

    )()()( aqFaqHaqHF Ka= 6.8x10-4

    4108.6log xpH

    47.2

    pH

    50.0

    10.0log

    70.017.3

    0.50M 0.10M

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    Adding Strong Acids/Bases

    to a Buffer Solutions Buffer Purpose: resistpHchange when limited

    amountsof strongacid or base is added

    Lab Exp. 18

    How happen:

    Addedacid or base reactsw/something in the buffer

    Addedacid or base is limiting

    Ex. Buffer:

    7

    Buffer Demo

    HA A-

    Buffered soln

    )()()( aqAaqHaqHA (W. Acid) (CB)

    http://www.youtube.com/watch?v=g_ZK2ABUjvAhttp://www.youtube.com/watch?v=g_ZK2ABUjvA
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    Adding a substance:

    1. H+added: REACTS w/ ____ in buffer

    Producing more ____

    2. OH-added: REACTS w/ ____ in buffer

    Producing more ____

    8

    HA A-

    Buffered soln

    )()()( aqAaqHaqHA (W. Acid) (CB)

    H+(aq) +A-(aq) HA(aq)

    HA A-

    Buffered soln

    OH-(aq) + HA(aq) A-(aq)

    HA A-

    HA A-

    A-

    HA

    HA

    A-

    +H2O(l)

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    Adding Strong Acid/Base

    to a Buffer Solution If the addedacid/base is strong, it isALL used up

    To calculate pH you use:a) ICE (must use MOLES!)

    b) H-Heq.(must use M)

    9

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    Sample Problems1. Calculate the pH of a 1.0L solution containing 0.10M NaF &

    0.50M HF, when 9.5mL of 2.1M HCl is added.(assume minimal/no volume change)

    HF(0.50M)

    NaF(0.10M)

    &

    1.0L Solnalready made

    BUFFER!

    Buffer:

    0.50M 0.10MH+(aq) + F-(aq)HF(aq)ADD HCl

    H+(aq)

    RXN:

    + F-(aq)HF

    (aq)

    Added: H+(aq) reacts w/

    W. Acid!

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    Sample Problems1. Calculate the pH of a 1.0L solution containing 0.10M NaF &

    0.50M HF, when 9.5mL of 2.1M HCl is added.(assume minimal/no volume change)

    +0.020-0.020

    0.08mol 0.52mol

    -0.020

    0

    I

    C

    E

    a) ICE Stoichiometry: (MOLES)Change by lower reactant value

    (0.10M)(1.0L)(2.1M)(0.0095L)

    0.10mol0.020 mol

    (0.50M)(1.0L)

    0.50mol

    1.0L 1.0L

    b) H-H: (M)

    AcidBase

    pKpH a log

    4108.6log xpH

    81.017.3 pH

    36.2pH

    52.008.0log

    H+(aq) + F-(aq) HF(aq)

    RXN:

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    Sample Problems2. Calculate the pH of a 1.0L solution containing 0.10M NaF &

    0.50M HF, when 9.5mL of 2.1M NaOH is added.(assume minimal/no volume change)

    12

    Buffer=

    a) ICE Stoich.: (MOLES) b) H-H eq (M)

    0

    +0.0200-0.020

    0.48mol 0.12mol0

    -0.020

    0

    I

    C

    E

    (0.50M)(1.0L)(2.1M)(0.0095L)

    0.50mol0.020 mol

    (0.10M)(1.0L)

    0.10mol

    1.0L 1.0L

    0.50M 0.10M

    AcidBase

    pKpH a log

    4108.6log xpH48.012.0log

    60.017.3 pH

    57.2pH

    OH-(aq)+ HF(aq) +F-(aq)H2O()

    H+(aq) + F-(aq)HF(aq)

    Added: OH-(aq) reacts w/

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    pH Comparison 0.50M HF: pH = 1.74

    Buffer0.50M HF & 0.10M NaF: pH = 2.47 pH inc. (more basic) due presence of a common ion

    Buffer0.50M HF & 0.10M NaF w/added9.5mL of

    2.1M HCl: pH = 2.35 pH dec. (more acidic) due additionof acid

    Buffer0.50M HF & 0.10M NaF w/added9.5mL of2.1M NaOH: pH = 2.59

    pH inc. (more basic) due additionof base 13

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    Sample Problem(What ifVolume changes?)

    1. Calculate the pH of a solution formed by mixing 65mL of0.20M NH4Cl with 75mL of 0.15M NH3. W. Base!

    NH3

    NH4Cl

    NH3

    NH4Cland

    75mL0.15M65mL

    0.20M

    65mL+75mL

    ??M

    Buffer:

    To Find Initial:Convert original M to moles,

    then back toMusing Total Vol

    =140.mL

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    Sample Problem(What ifVolume changes?)

    1. Calculate the pH of a solution formed by mixing 65mL of0.20M NH4Cl with 75mL of 0.15M NH3.

    BUFFER, MUSTuse ICE table!!

    15

    )(NH4 aq

    0-x

    0.093+x0

    +x

    0.080-x

    I

    C

    E

    (0.20M)(065L)(0.15M)(0.075L)

    0.013mol0.01125 mol0.140L

    )(NH3 aq O(l)H2

    0 0

    0.140L

    0.080M 0.093M

    +x

    x

    5

    108.1

    x]080.0[

    ]][093.0[

    x

    xx

    Kb

    ]080.0[

    ]][093.0[108.1

    5 xx

    Mxx5

    105.1

    ][

    OH

    W. Base!

    )(OH aq

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    Sample Problem(What ifVolume changes?)

    1. Calculate the pH of a solution formed by mixing 65mL of0.20M NH4Cl with 75mL of 0.15M NH3.

    BUFFER, MUSTuse ICE table!!

    16

    )(NH4 aq

    0-x

    0.093+x0

    +x

    0.080-x

    I

    C

    E

    (0.20M)(065L)(0.15M)(0.075L)

    0.013mol0.01125 mol0.140L

    )(NH3 aq O(l)H2

    0 0

    0.140L

    0.080M 0.093M

    +x

    x

    W. Base!

    )(OH aq 100080.0

    105.1%

    5

    xx

    I

    %019.0% I

    ]105.1log[5

    xpOH

    82.4pOH

    82.400.14 pH

    18.9pH

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    Sample Problem (Volume changes?)2. Calculate the pH of a solution formed by mixing 65mL of

    0.20M NH4Cl with 75mL of 0.15M NH3& adding 15.3mL

    of 0.17M NaOH.

    17

    O(l)H)(NH 23 aq

    -0.0026-0.0026

    0.01385mol0mol

    +0.0026

    0.0104mol

    I

    C

    E

    (0.15M)(075L)(0.20M)(0.065L)

    0.01125mol0.013 mol

    0.155L

    )(NH4 aq )(OH- aq

    0

    VT=65mL+75mL+15.3mL=155.mL

    0.155L

    0

    0

    a) ICE Stoich: (MOLES)

    (0.17M)(0.0153L)

    0.0026 mol

    0.00671M 0.0894M

    b) H-H: (M)

    AcidBase

    pKpH a log

    14

    101

    xKK ba

    145

    101108.1

    xxKa

    10106.5 xKa

    Try on ownBuffer=

    Added: OH-(aq) reacts w/

    0.15M 0.20MNH4

    +(aq) + OH-(aq)NH3(aq)+ H2O(aq)

    (NH3is a base, K

    b= 1.8x10-5)

    Must solve for Ka

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    Sample Problem (Volume changes?)2. Calculate the pH of a solution formed by mixing 65mL of

    0.20M NH4Cl with 75mL of 0.15M NH3& adding 15.3mL

    of 0.17M NaOH.

    18

    O(l)H)(NH 23 aq

    -0.0026-0.0026

    0.01385mol0mol

    +0.0026

    0.0104mol

    I

    C

    E

    (0.15M)(075L)(0.20M)(0.065L)

    0.01125mol0.013 mol

    0.155L

    )(NH4 aq )(OH- aq

    0

    VT=65mL+75mL+15.3mL=155.mL

    0.155L

    0

    0

    a) ICE Stoich: (MOLES)

    (0.17M)(0.0153L)

    0.0026 mol

    0.00671M 0.0894M

    b) H-H: (M)

    AcidBase

    pKpH a log

    Try on ownBuffer=

    Added: OH-(aq) reacts w/

    0.15M 0.20MNH4

    +(aq) + OH-(aq)NH3(aq)+ H2O(aq)

    125.025.9 pH

    0671.00894.0

    log

    38.9pH

    10

    106.5log

    xpH

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    Buffer Capacity Buffer Capacityamount of acid/baseadded

    before a significantpH change occurs

    In demo video: needed to count drops of NaOHadded Took ~30 drops to turn green

    Took ~35 drops to turn blue/violet

    Depends on conc.of acid/base used to prepare buffer Which has a greater buffering capacity?

    19

    1 MHF & 1 M NaF0.1M HF & 0.1 M NaF

    More initialacid/baseto react with

    addedacid/base

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    Buffer Range Buffer range - pHrange where buffer is effective

    Want conc.of acid/base & conjugate to be similar

    Ex: 0.50M HF & 0.10M NaF

    If conc of 1 component in buffer is > 10x the conc of theother, buffering action is poor

    Choose an acidwhose pKais close to the desired pH

    20

    pKaofunitpH1Range

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    Questions:1. Which of the following will have the worstbuffering

    range?

    A. 0.1M HA and 0.1M A-

    B. 0.2M HA and 0.1M A-

    C. 0.1M HA and 1.5M A-

    D. 1.0M HA and 1.0M A-

    21

    Difference ismore than 10x

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    Questions:2. You wish to make a buffered solution with a pH=7.0,

    which acid will be the best to use?

    A. HNO2: Ka = 4.5x10-4 pKa= 3.35

    B. HClO: Ka= 3.0x10-8 pKa= 7.52

    C. H3PO4: Ka= 7.5x10-3 pKa= 2.12

    D. H2CO3: Ka= 4.3x10-7 pKa= 6.37

    E. HBrO: Ka= 2.5x10-9 pKa= 8.60

    22

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    Acid/Base Titration Introduced in Chapter 4

    Indicatorschemicals that changecolorwhen a solution turns fromacidic to basic

    Phenolphthalein

    Acid = Clear

    Base = Pink

    23

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    Acid/Base Titration Titration CurvepHvs. volumeof titrantadded

    Titrant- liquid in buret

    Equivalence Pointstoichiometric# of moles of acid =

    # mols base reacted

    Endpointwhere indicator changescolor permanently

    Just past the equivalence point

    24

    TitrationCurve

    Equiv. pt

    Endpt

    http://www.youtube.com/watch?v=yirkozUyG74http://www.youtube.com/watch?v=yirkozUyG74http://www.youtube.com/watch?v=yirkozUyG74http://www.youtube.com/watch?v=yirkozUyG74http://www.youtube.com/watch?v=yirkozUyG74
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    pH at Various

    Titration Points 2 types of titrations

    1. Strong/Strong

    2. Weak/Strong

    What is happening to pH @ 4 different points

    A. InitialpH

    B. Beforeequivalence pt

    C. @equivalence pt

    D. Afterequivalence pt

    25

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    pH at VariousTitration Points

    1. Strong Acid

    &Strong Base

    26

    1 Strong Ac Strong Base:

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    1. StrongAc - StrongBase:(NaOH added to HCl)

    A. Initial pH:beforeadding base

    NoNaOH added, onlyHCl present

    pH =Very acidicB. Beforeequivalencept:

    HCl & NaOH react

    Baselimiting

    Acidexcess

    pH=slowlymore basic,b/c less acid in excess

    Raises rapidlynear

    equivalence pt.27

    )(l(aq)a)(a)( 2 lOHCNaqOHNaqHCl

    A

    100mL0.50M

    ?mL0.10M

    pH=0.30

    BpH=0.44

    pH=2.17

    1 Strong Acid Strong Base:

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    C. At equivalencept: HCl & NaOH react

    Moles acid=Moles of base

    CompletelyNeutralized pH = 7.00

    How get pH when only

    NaCl & H2O present?- Waterdissociates

    28

    C

    H2O (l) H+(aq) + OH-(aq) 14101 xKw

    M101]OH[]H[ 7 x

    1. Strong Acid-Strong Base:(NaOH added to HCl)

    pH=7.00

    )(l(aq)a)(a)( 2 lOHCNaqOHNaqHCl 100mL0.50M

    ?mL0.10M

    1 Strong Acid Strong Base:

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    D. After equivalencept: HCl & NaOH react

    Acid limiting

    Completely consumed

    Base excess

    pH = slowly more basic

    29

    D

    1. Strong Acid-Strong Base:(NaOH added to HCl)

    )(l(aq)a)(a)( 2 lOHCNaqOHNaqHCl 100mL0.50M

    ?mL0.10M

    pH=11.82pH=13.20

    1 St A id St B

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    mL NaOH pH

    0 0.30

    10.0 0.44

    49.0 2.17

    50.0 7.00

    51.0 11.82

    80.0 13.22

    1. StrongAcid - StrongBaseSummary: (NaOH is added to HCl)

    Why does pH change drasticallynear equivalence point ()?

    pH dependent on MOLESpresentAFTERreaction!

    1 St A id St B

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    At equivalencepoint: OHH

    nn1

    2

    3

    4

    MOLESpresentAFTERreacting0.050

    0.040

    0.001

    00

    0

    0

    0

    0

    0

    0.001

    0.030

    OHNaClNaOHHCl 2

    1. StrongAcid - StrongBaseSummary: (NaOH is added to HCl)

    StepmL

    NaOH

    n H+

    (after rx n)

    n OH-

    (after rxn )

    1 0

    2 10.0

    2 49.0

    3 50.0

    4 51.0

    4 80.0

    What does a

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    What does aStrong Base-Strong Acid

    Titration Look Like?

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    Question: Where is the end point for the following titration

    curve?

    33

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    pH at VariousTitration Points

    2. Weak Acid

    &

    Strong Base

    34

    2 Weak Acid - Strong Base:

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    A. Initial pH:beforeadding base

    NoNaOH added, onlyHC2H3O2present

    pH =acidic

    35

    A

    )()((aq)(aq) 2232232 lOHaqOHCOHOHHC

    2. WeakAcid - StrongBase:(NaOH added to HC2H3O2)

    100mL0.50M

    ?mL0.10M

    pH=2.52

    2 Weak Acid - Strong Base:

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    B. Beforeequivalence pt: HC2H3O2& NaOH react

    Baselimiting

    Acidexcess pH =slowlymore basic,

    b/c less acid in excess

    Raises rapidlynear

    equivalence pt.

    A BUFFER soln!

    HC2H3O2& conjugate

    base (C2H3O2-

    ) present 36

    B

    OHOHCOHOHHC 2232232

    2. WeakAcid - StrongBase:(NaOH added to HC2H3O2)

    100mL0.50M

    ?mL0.10M

    pH=5.69

    2 Weak Acid - Strong Base:

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    C. At equivalencept: HC2H3O2 & NaOH react

    Moles acid=Moles of base

    NOT completely neutralized!!

    Have conjugatebase (C2H3O2-)

    pH > 7

    37

    C

    )(OH)(OHHCO(l)H)(OHC 2322232 aqaqaq

    OHOHCOHOHHC 2232232

    2. WeakAcid - StrongBase:(NaOH added to HC2H3O2)

    100mL0.50M

    ?mL0.10M

    pH=9.25

    2 Weak Acid - Strong Base:

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    D. After equivalence pt: HC2H3O2 & NaOH react

    Acidlimiting

    Completely consumed Baseexcess

    pH = gets more basic

    D

    OHOHCOHOHHC 2232232

    2. WeakAcid - StrongBase:(NaOH added to HC2H3O2)

    100mL0.50M

    ?mL0.10M

    pH=11.82

    pH=13.20

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    0 20 40 60 80 1000

    2

    4

    6

    8

    10

    12

    14

    pH

    Volume of NaOH added (mL)

    Titration Curve

    Comparisons1. Initial pH:

    S/Sis lower, more acidic

    DissociatescompletelymoreH+in soln

    2. After Equivalence:

    Curves are the same Amount of excess

    OH-is the same

    W. acid S. base

    S. acid S. base

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    0 20 40 60 80 1000

    2

    4

    6

    8

    10

    12

    14

    pH

    Volume of NaOH added (mL)

    Titration Curve

    Comparisons3. @ Equivalence point:

    S/Smore rapidrise

    Volumeneeded is same

    pHdifferent S/S = 7.00

    W/S > 7

    - b/c conjugate base

    present

    VNaOH(HAc) =VNaOH(HCl)

    W. acid S. base

    S. acid S. base

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    0 20 40 60 80 1000

    2

    4

    6

    8

    10

    12

    14

    pH

    Volume of NaOH added (mL)

    Titration Curve

    Comparisons4. Before Equivalence point:

    W/Sis a bufferedsoln!

    Acid& conjugate basepresent

    TitrationComparison

    (extra)

    W. acid S. base

    S. acid S. base

    http://www.youtube.com/watch?v=xRVTdDrrtLchttp://www.youtube.com/watch?v=xRVTdDrrtLchttp://www.youtube.com/watch?v=xRVTdDrrtLchttp://www.youtube.com/watch?v=xRVTdDrrtLc
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    Titration Curve

    Comparisons Differences morepronounced, the weakerthe acid

    Weaker acids have more basicequivalence points

    Can determine Kaof aweakacid from thetitration curve

    In a bufferedsystem: AcidBase

    pKpH a log

    0apKpH

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    Titration of

    Polyprotic Acids Polyprotic acidcontains 1 or more ionizable H

    atoms

    Ex: H3PO3=

    H2C4H4O6=

    Ionization occurs 1 H atom at a time,thus multipleequivalence pts exist

    Ex: H3PO3

    43

    3H+

    2H+

    H2PO3-(aq)

    H2PO3-(aq) HPO32-(aq)

    (aq)H(aq)POH 33

    (aq)H

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    Titrating w/Indicators How do you know what indicatorto use?

    Ideallyit should change at/nearthe equivalence pt.

    Since pH changes so fast here, as long indicator changesanywhere on rapid rise of titration curve, all is ok

    44

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    Titrating w/Indicators Are the following goodindicators for the titration

    shown?

    45

    1. Phenolphthalein: 2. MethylRed:

    Yes, change colorin rapid rise

    No, doesnt change colorin rapid rise

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    Titrating w/Indicators What if not given a picture diagram for color change?

    Indicators are acids thus have a Ka

    Indicators change color when pHof the system equalstheir pKa!

    Want pKa of Indicator to be as close to pH of

    endpoint/equivalence as possible 46

    IndHHInd

    Color 1 Color 2

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    Questions:1. Which indicators would work for the titration shown?

    47

    Both,b/c on rapid decline

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    Questions:2. A laboratory worker is titrating an unknown solution of a

    weak acid with a strong base. Which indicator shouldthey choose given the following titration curve?

    A. Pentamethoxy red: pKa = 1.8

    B. Congo red: pKa = 4.0

    C. Azolitmin: pKa = 6.5

    D. Phenolphthalein: pKa = 9.0

    E. Trinitrobenzoic acid: pKa = 12.7

    48

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    Solubility Equilibria Some ions when combined form insolublesalts

    PrecipitationRxns (Chap 4, solubility Rules)

    Saturated solutioncontains undissolvedsolute

    However, somedoes dissolve (SLIGHTLY!)

    49

    PbI2

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    Solubility Equilibria Solubility-Product Constant, Kspequilibrium

    constant for a slightlysoluble(or nearlyinsoluble)

    ioniccompound Degreeto which a solid is soluble in water

    NOsolidsor liquidsin equilibrium expression!

    Appendix D

    50

    )(2I)(Pb(s)PbI 22 aqaq

    22

    sp ]][I[PbK

    5107.1 x

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    Sample Problem If 0.0012 mols PbI2(s) dissolves in 1.0 L water, what is

    its Kspvalue?

    51

    22 ]][[ IPbKsp0.0012M 0 0

    2(0.0012)0.0012-0.0012

    0M 0.0012M 0.0024M

    2]0024.0][0012.0[spK

    9

    109.6

    xKsp

    I

    C

    E

    )(2I)(Pb(s)PbI 22 aqaq

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    52

    Solubility vs.

    Solubility Product, Ksp Solubilitygrams dissolved to form a saturated

    solution Units = grams/L

    Molar Solubilitymolesdissolved to form asaturatedsolution Units = mols/L

    Kspequilibrium constant for ionic solid & itssaturatedsolution

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    53

    Sample Problem If the Kspof BaF2is 1.7x10

    -6, calculate the molarsolubility.

    22 ]][[ FBaKsp)(2)((s)2

    2 aqFaqBaBaF

    26]2][[107.1 xxx

    364107.1 xx

    Mxx

    3

    105.7

    [Ba2+]

    1:1 ratio of Ba2+:BaF2,molar solubility of BaCl2= 7.5x10

    -3M

    x 0 0

    2(x)+x-x

    0M x 2x

    I

    C

    E

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    Factors Affecting Solubility1. Common Ion EffectAdding a common ion

    decreasesthe solubilityof the partially soluble salt

    AKA Le ChteliersPrinciple

    Adding BaCl2(Ba2+) or NaF (F-) shifts equilibrium

    54

    )(2)((s) 22 aqFaqBaBaF

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    Sample Problem What is the molar solubility of BaF2in 0.15M NaF?

    55

    )(2)((s) 22 aqFaqBaBaF

    0 0.15

    x 2x

    x 0.15+2x

    22 ]][[ FBaKsp

    6107.1 x

    26]15.0][[107.1 xx

    Mxx5

    1056.7

    I

    C

    E

    2]215.0][[ xx x

    -x

    0M

    small

    Just BaCl2= 7.5x10-3M

    Decreased

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    Factors Affecting Solubility2. pH:Almostany ioniccompound will dissolve if the

    pH of the solution is altered

    Solubilityincreasesif acidis added to a basicanion

    Ex: Add HNO3to BaF2: H+from HNO3reacts w/F

    -from BaF2

    Adding more acid (H+) shifts equilibrium

    56

    )(aqH )( aqF )(aqHF22 2

    )(2)((aq)2)(2

    2 aqHFaqBaHsBaF

    )(2)((s) 22 aqFaqBaBaF

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    Factors Affecting SolubilityComplexes

    3. In the presence of suitable Lewis bases, metalionscan form complexes:

    57

    (aq)S(aq)FeFeS(s) 22

    (aq)CNFe(aq)6CN(aq)Fe -462

    Ksp= 6.31x10-18

    Kf= 1.00x1035

    (aq)S(aq)CNFe(aq)6CNFeS(s)-2-4

    6

    K = 6.31x10

    17

    f for formation(of a complex).

    More in Chapter 23, but will use this idea in Experiment 19!

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    Precipitation &Separation of Ions

    How do you know if a precipitatewill form?

    Need to compare Kspto your actualconditions Qsp

    IF:

    Qsp= Ksp: Equilibrium (saturated soln)

    Qsp> Ksp: Pptoccurs

    Qsp< Ksp: Dissolutionoccurs

    58

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    Sample Problems

    1. [Ca2+] in human blood is 0.0025M & Calcium oxalate (CaC2O4)makes kidney stones. If Ksp= 2.3x10

    -9for calcium oxalate,will it ppt in a patient with [C2O4

    -2] = 1.0x10-6?

    59

    ]][[ 2422

    OCCaQsp

    ]100.1][0025.0[ 6 xQsp9105.2 xQsp

    Qsp> Ksp

    Not at equilibrium, use Qsp

    Ppt occurs & Kidney stones form (OUCH!!)

    Sample exercises (in book)17.15 & 17.16

    very helpful!

    )()((s)2

    42

    2

    42 aqOCaqCaOCaC

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    Sample Problems

    2. A solution contains 1.0x10-2M Ag+& 2.0x10-2M Pb2+.When Cl-is added, both AgCl (Ksp=1.8x10

    -10) & PbCl2(Ksp=1.7x10

    -5) can precipitate. Which precipitates first?

    60

    ]][[ ClAgKsp22 ]][[ ClPbKsp

    Solve for [Cl-]

    10108.1 x

    8108.1][

    xCl

    225 ]][100.2[107.1 Clxx2

    109.2][

    xClAnything abovethis will ppt

    AgCl ppt first, b/c smaller [Cl-]

    ]][100.1[ 2 Clx

    Anything abovethis will ppt

    ua tat ve Ana ys s

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    Determines presenceorabsenceof metalions

    Noinfo about amount

    5 groups

    1. Insoluble Cl-

    2. InsolubleAcid S-

    3. Insoluble Base S-&OH-

    4. Insoluble PO4-3

    5. Soluble alkali metal& NH4

    +ions

    61

    y(selective precipitation)

    (LAB 22)

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    Sample Question

    1. Which ion will precipitate whenphosphate ion is added to a

    solution containing all of theions below

    A. K+

    B. Ba2+

    C. Na+

    D. NH4+

    62

    Summary Chap. 17

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    Summary Chap. 171. Common Ion Effect

    2. Buffers:

    Calculationsa) Ice Table

    b) Henderson-Hasselbalch eq.

    3. Adding Strong Acid or Base to a buffer

    RXN occurs! ICE table (MOLES)

    H-H eq. (M)

    4. Acid/Base Titration

    S/S

    S/W

    Compare titration curves

    5. Solubility equilibria

    6. Qualitative analysis

    acidbasepKpH a log