Unit 8-Acids and Bases Flashcards

1
Q

Kw

A

ion-product constant for water
Illustrates amount of water ionized
Can be used for acids and bases
Kw = [H+] [OH-]

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2
Q

Kw at 25 degrees Celsius

A

1.0 * 10^-14

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3
Q

Type of solution based on concentration of H+ and OH-

A

[H+] > [OH-] = acidic
[H+] = [OH-] = neutral
[H+] < [OH-} = basic

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4
Q

pH =

A

-log [H3O+]
pOH = -log [OH-]
Sig figs for pH is decimals

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5
Q

As [H3O+] increases…

A

The pH decreases
When concentration changes by a factor of 10, pH will change by a factor of 1

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6
Q

Sum of pH and pOH at 25 degrees Celsius

A

14.00

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7
Q

Autoionization of water is…

A

Endothermic

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8
Q

Weak Acids

A

Partially ionize in water so to solve, you have to use a Ka expression

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9
Q

Large Ka =

A

stronger acid

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10
Q

Percent Ionization

A

(x/[initial concentration of weak acid]) *100
Stronger acids have a greater percent ionization
As the concentration of a weak acid decreases, the percent ionization increases because products decrease more than reactants so reaction shifts right to form more ions

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11
Q

Kb

A

Base dissociation constant
Refers to weak base added to water and forming conjugate acid and hydroxide

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12
Q

Anions of Weak Acids

A

F- = weak base forms HF = weak acid (conjugate acid)
HCl = strong acid forms Cl- =negligible

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13
Q

Relationship between Ka and Kb

A

Stronger acids have weaker conjugate bases
Stronger acids have negligible conjugate bases
Ka * Kb = Kw = 1.0 * 10^-14
pKa + pKb = 14.00

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14
Q

Strong Acid + Strong Base

A

Use before after and stoichiometry to find limiting reactant
ER determines pH

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15
Q

Weak Acid + Strong Base

A

Use stoichiometry (moles) to find LR and ER

Strong base excess = determines pH
Weak acid and conjugate base are excess = both determine pH
Both substances are limiting so conjugate base is left = determines pH

ER dissolves in water so…Use ICE table
Ka or Kb if weak acid and weak base are present
Only weak base = use Kb ICE table

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16
Q

Half-Equivalence Point

A

pH = pKa
pOH = pKb
([weak acid] = [conjugate base])

17
Q

Buffers

A

Solutions that contain a weak acid-conjugate base or weak base-conjugate acid pair
Withstands pH changes when strong acid/base is added to them

18
Q

Two ways to make a buffer

A

Add a salt of the weak acid or base
Ex. Add sodium acetate to a solution of acetic acid

Add a strong acid/base to a solution of weak base or weak acid
Ex. Add sodium hydroxide to a solution of acetic acid

19
Q

Strong Acid-Strong Base Titrations (Base is being added to the Acid)

A

Initial pH = calculate with concentration of initial acid
Between initial pH and equivalence point = added base is LR so perform stoichiometry to find concentration of acid after base was added. Use this concentration of acid to find pH
Equivalence point = 7.00
After equivalence point = base is excess so concentration of base finds pH

20
Q

Weak Acid-Strong Base Titrations (Base is added to the Acid)

A

Initial pH = use Ka ICE table to find out how much dissociated
Between initial pH and equivalence point = added base is LR; stoichiometry to find concentration of weak acid and conjugate base after base was added. Use ICE table to calculate pH; half-way is pH = pKa
Equivalence point = HA is all converted into CB so use Kb ICE table
After equivalence point = HA is LR so excess base determines pH

21
Q

Determining Ka from Titration Curve

A

Find volume of base needed to reach equivalence point and half it
This volume is the half-way point/half-equivalence point
pH = pKa

22
Q

Weak Acid-Strong Base vs. Strong Acid-Strong Base

A

Solution of weak acid has higher initial pH
pH changes is smaller in weak acid titration
pH equivalence point is above 7.00 in weak acid titration

23
Q

Titrations of Polyprotic Acids

A

Polyprotic Acids have more than one proton
It has 2+ Ka values and 2+ equivalence points

24
Q

Weak Base-Strong Acid Titrations Graph (Acid added to Base)

A

Opposite of weak acid-strong base titrations
Initial pH = ICE table to find concentration of base dissolved
pH at equivalence point = conjugate acid present so ICE table
After equivalence point = excess strong acid determines pH

25
Factors that Affect Acid Strength
Bond Polarity (Bond Polarity increases, stronger acid forms) Bond Length (Bond strength decreases, stronger acid forms Conjugate Base Stability (greater stability of CB, stronger acid; when resonance structures can be drawn for the conjugate base, this means that the acid has great stability due to the delocalized pi electrons)
26
Binary Acid Trends
Within a group=Bond strength is the most important factor Down a group = bond strength decreases and strength of acid increases Within a period=Bond polarity is the most important facotr Across a period = Bond polarity increases and strength of acid increases
27
Oxyacid
Contains an atom bonded to 1+ oxygen atoms
28
Inductive Effect
The attraction of electrons in adjacent bonds by more EN atoms
29
Rules of Oxyacid Strength
Same # of O-H groups and O atoms = acid strength increases as the EN value of Y increases Same central Y atom - acid strength increases with increase in # of O atoms
30
Comparing pH and PKa to find concentration of acid and conjugate base in buffer solution
pH < pKa = acid forms a higher concentration in the original solution pH > pKa = conjugate base forms a higher concentration in the original solution
31
When does an indicator change color?
Around the equivalence point; bc of rapid change in pH it changes color not exactly at the equivalence point
32
Henderson-Hasselbalch Equation
Used to find the pH of a buffer pH = pKa + log [A-]/[HA] X in the ICE table is essentially negligible
33
Using Henderson-Hasselbalch Equation to determine information of a reaction
Acid and conjugate base concentrations are equal:pH=pKa Conjugate base concentration than greater than acid: pH > pKa Conjugate base concentration is less than acid: pH
34
Buffer Capacity
Amount of acid/base the buffer can neutralize before it starts changing pH Depends on concentrations of weak acid and conjugate base use to make buffer A buffer can be made for any pH by adjusting relative concentrations of the weak acid/weak base
35
Higher concentrations =
greater buffer capacity
36
Making a buffer at a specific pH
Choose an acid with a pKa close to desired pH (H+ concentration) for the buffer Henderson-Hasselbalch equation can be used to determine ideal ratio for a certain pH