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My Packs: UWO (CHEM 1302) > Chapter 3: 3.3 Weak Acids and Bases > Flashcards

Chapter 3: 3.3 Weak Acids and Bases Flashcards

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1
Q

How are acids and bases often defined?

A
  • Acids: Substances that increase hydrogen ion concentration [H+] in solution
  • Bases: Substances that increase hydroxide ion concentration [OH-] in solution
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2
Q

What is the difference between a strong acid/base vs. a weak acid/base?

A

Strong acids and bases completely ionize in solution, whereas weak acids and bases do not ionize completely (only proceed until equilibrium)

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3
Q

What is used interchangeably for the definition of strong acids?

A

Strong acids increase the [H+] or [H3O+] concentration of the solution (H+ combining with H2O gives the H3O+)

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4
Q

True or False:

Acid-base equations use equilibrium arrows

A

Not necessarily, strong acid/base reactions use unidirectional arrows as they ionize completely

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5
Q

Define:

Acids and Bases, according to the Arrhenius theory

A
  • Acid: Produces H3O+ ions in water
  • Base: Produces OH- ions in water
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6
Q

Define:

Acids and Bases,
according to the Brønsted-Lowry theory

A
  • Acid: Proton donor
  • Base: Proton Acceptor
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7
Q

True or False:

Weak acid/base reactions use two directional arrows

A

True, as they proceed until an equilibrium is achieved between reactants and products

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8
Q

State the notation for:

Equilibrium constants of weak acids and weak bases

A
  • Weak acids: Ka
  • Weak bases: Kb
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9
Q

Define:

Lewis Acid and Lewis Base

A
  • Lewis Acid: A substance that can accept a pair of electrons from another atom to form a bond
  • Lewis Base: A substance that donates a pair of electrons to another atom to form a bond
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10
Q

In terms of Lewis definition, what would amines classify as? Why?

A

Lewis Bases
* They have a lone pair of electrons that they can donate, making them a Lewis Base

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11
Q

In terms of Lewis definition, what would metal cations classify as? Why?

A

Lewis Acids
* As they are cations they form complex ions with Lewis Bases known as coordination complexes

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12
Q

In terms of Lewis definition, what would oxides of nonmetals classify as? Explain

A

Lewis acids
* For example, CO2 accepts electrons from OH- to form HCO3-, making it a Lewis acid

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13
Q

In the case of weak acids and weak bases, what would the K value be?

A

Less than 1, as they cannot ionize completely

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14
Q

In terms of acids/bases, the larger the K value…

A

The greater the ionization

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15
Q

How are Ka and Kb values often expressed? Show the notation

A

In a logarithmic scale:
* pKa = -logKa
* pKb = -logKb

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16
Q

True or False:

In terms of weak acids, there are some acids that are “weaker” and some that are “stronger”

A

True, “stronger” and “weaker” are relative terms

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17
Q

State the Ka and pKa for:

  1. Stronger weak acid
  2. Weaker weak acid
A
  1. Larger Ka (smaller pKa)
  2. Smaller Ka (larger pKa)
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18
Q

State calculation method/result of:

  1. pH
  2. pOH
  3. pH + pOH
A
  1. -log[H+]
  2. -log[OH-]
  3. 14
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19
Q

Defineand give the notation for:

Percent Ionization

A

The amount of the weak acid ionized (or dissociated) expressed as a percent of the original concentration of the acid, using the relationship:
* (x/c)(100%) = α

q

20
Q

How are x and c found in the calculation for percent ionization?

A

c (initial concentration) and x (amount that ionizes) are calculated using Ka/Kb and ICE tables

21
Q

True or False:

When the quadriatic formula is involved in calculating the amount that ionizes, we only use the positive value

A

True, as only a positive concentration is possible

22
Q

In the process of calculating percent ionization, how can we determine if we can assume c-x=c?

A
  1. Calculate the ratio for c/Ka. If ratio is less than 400, quadriatic formula should be used
  2. If α is less than 5%; this is less helpful as it usually requires knowing x already
23
Q

What is the main rule in calculating the initial concentration of the weak acid?

A

If you know x, USE IT

24
Q

What is the relation between diluteness and percent ionization?

A

The more dilute the solution of a weak acid or base, the greater the percent ionization

25
Q

State:

The trend with dilution and pH

A

The more dilute the solution, the closer to pH 7 the solution gets

26
Q

Define:

Conjugate base of an acid

A

The species formed when the acid has donated a proton

27
Q

Define:

Conjugate acid of a base

A

The species formed when the base has accepted a proton

28
Q

How will a conjugate base behave in a solution?

A

Like a weak base

29
Q

How will a conjugate acid behave in a solution?

A

Like a weak acid

30
Q

What is Kw known as?

A

The ion product of water OR the equilibrium constant for the ionization of water

31
Q

What is Kw at 25 °C?

A

1.0 * 10^-14

32
Q

State the relation between:

  1. Ka
  2. Kb
  3. Kw
A

Ka * Kb = Kw

33
Q

State the relation between:

  1. pKa
  2. pKb
A

pKa + pKb = 14

34
Q

True or False:

Strong acids have conjugate bases

A

Technically true, they are referred to as spectator ions and do not affect pH at all

35
Q

True or False:

The stronger the weak acid, the stronger the conjugate base

A

False, the stronger the weak acid, the weaker the conjugate base

36
Q

What are characteristics of spectator ions?

A
  • Do not react with water
  • Does not affect pH of solution
  • Related to strong acids and strong bases
37
Q

Define:

Salts

A

An ionic solid containing cations (other than just H+) and anions

38
Q

What happens when a salt dissolves in water?

A

The cation and anion separate from each other

39
Q

True or False:

Salts will completely dissolve

A

False, they may not be very soluble

40
Q

True or False:

The dissolved portion of salts is completely ionized

A

True, this is always the case

41
Q

What are cations that do not have any effect on pH known as?

A

Spectator ions

42
Q

In cases where both the cation and anion can affect pH, how do we determine the pH of the salt/solution?

A
  1. If Ka > Kb, the salt is acidic
  2. If Kb > Ka, the salt is basic
43
Q

Define:

Amphoprotic anion/Amphoteric species

A

A species that can act as both an acid or a base

44
Q

Define:

Polyprotic weak acids

A

They contain more than one ionizable hydrogen atom

45
Q

How do polyprotic acids ionize?

A

In stages, each with a different Ka value

My Packs: UWO (CHEM 1302) (15 decks)

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