AP Chemistry: Unit 8

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Autoionization

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52 Terms

1

Autoionization

pure water has an equilibrium in the production of H3O+ and OH- ions (It will act as a Bronsted-Lowry acid and base)

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2

The equilibrium constant for the autoionization of water

Kw=[H3O+][OH-] Kw= 1 × 10-14

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3

[H3O+]>[OH-]

acidic

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4

[H3O+]<[OH-]

Basic (Alkaline)

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5

[H3O+]=[OH-]

Neutral

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6

What does “p” direct you to do?

to the usage of -log of the measurement we’re using

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7

pH=

-log[H3O+]

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8

[H3O+][OH-]=

1 × 10-14

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9

[H3O+]=

10 TO THE -pH

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10

[OH-]=

10 TO THE -pOH

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11

pOH+pH=

14

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12

pOH=

-log[OH-]

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13

Ka*Kb=

1 × 10-14

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14

As temperature increases, what happens to Kw?

It increases

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15

Strong acids have

weak H-X bonds (HCl)

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16

Weak acids have

strong H-X bonds (HF); do not experience a strong induced dipole force.

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17

Oxoacids

contain an atom bonded to one or more oxygen atoms, sometimes with hydrogens attached.

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18

Inductive effect

when electrons in adjacent bonds are attracted to more electronegative atoms. A stronger inductive effect creates more polarity in the molecule as e- move away to the electronegative atoms and makes it more ionizable (a stronger acid)

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19

Weak acids in terms of polarity

weak acids will have a less inductive effect, which leads to less attraction of e- to electronegative atoms, making it less ionizable.

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20

A strong acid will produce a

weak conjugate base

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21

A weak acid will produce a

strong conjugate base

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22

Strong bases

attract more protons

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23

Factors that affect base strength

  1. How easily the lone pair picks up a hydrogen ion

  2. Stability of the ions formed

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24

Strong base will produce a

weak conjugate base

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25

Weak base will produce

a strong conjugate acid

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26

As Kb or Ka increases

the strength increases

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27

Relative concentrations of an acid and its conjugate base can be predicted by comparing

the pH of a solution to the pKa of the acid in that solution

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28

pH<pKa

the acid form is greater in the buffer solution

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29

pH>pKa

the conjugate base is greater in the buffer solution

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30

Equivalence point

the number of moles of titrant added is exactly sufficient to react completely with the number of moles of the titrated species in the sample.

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31

Endpoint

point at which the indicator undergoes a color change in a titration

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32

Buffers

a solution that is resistant to changes in pH when a strong acid/base is added because it is a solution of a strong acid + conjugate base or strong base + conjugate acid

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33

pH of a buffer

includes the pKa of the acid an

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34

Key assumptions of the Henderson-Hasselbalch Equation

Equil. concentrations of acid and conjugate base are approx equal to the initial concentrations

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35

pH (according to the Henderson-Hasselbalch Equation)

pKa + log([A-]/[HA])

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36

The higher the buffer concentration

the greater the amount of acid or base it can neutralize - pH doesn’t change

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37

What should you do in order to have the buffer solution be able to control the pH at the desired value?

Choosing an acid with a Ka close to the intended value of [H3O+] - Finding the ideal ratio of acid : conjugate base

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38

Common strong acids

HCl, HNO3, HClO4, H2SO4, HBr, HI

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39

Common strong bases

LiOH, NaOH, KOH, RbOH, CsOH, Ca(OH)2, Ba(OH)2, Sr(OH)2

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40

What can you use to find pOH and pH of strong acids/bases?

Basic stoichiometric ratios to find the concentration of H+ or OH- when the strong base/acid dissociates

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41

% ionization

[H+]equilibrium concentration/[Acid]initial concentration * 100

[OH-]equilibrium concentration/[Base]initial concentration * 100

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42

Net ionic equation for strong base + strong acid

H+ + OH- → H2O(l)

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43

Weak acid + Strong base

Weak acid + Strong base → Water + Conjugate base

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44

Strong acid + Weak base

Strong acid + Weak base → Water + conjugate acid

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45

Weak acid + Weak base

Check your Ka and Kb values (Ka>Kb - ACIDIC)

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46

pH=pKa at the

half-equivalence point where the concentration of the weak acid/weak base is = to the conjugate acid/base

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47

Strength of an acid

ELECTRONEGATIVE ATOMS - # OF OXYGENS

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48

Common weak bases have

nitrogen and hydrogen (NH3)

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49

An indicator should have a pKa value close to

the pH value of the equivalence point

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50
<p>What kind of titration is this?</p>

What kind of titration is this?

Strong acid titrated with strong base - Equivalence point is 7 pH

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51
<p>What kind of titration is this?</p>

What kind of titration is this?

Weak acid titrated with strong base - Equivalence point is higher than 7 pH

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52
<p>What kind of titration is this?</p>

What kind of titration is this?

A strong acid titrated with weak base - Equivalence point is lower than 7 pH

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