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AP Chemistry > Chapter 16 - Acid-Base Equilibria > Flashcards

Chapter 16 - Acid-Base Equilibria Flashcards

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1
Q

16.1

Define “Arrhenius acid”.

A

Substance that increases concentration of H+ ions in H2O

Applies only to solutions

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2
Q

16.1

Define “Arrhenius base”.

A

Substance that increases concentration of OH- ions in H2O.

Applies only to solutions

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3
Q

16.2

Define “Bronsted-Lowry acid”.

A
  • Donates a proton to another substance.
  • Doesn’t only apply to solutions
  • Must have a H atom that it can lose as an H+ ion
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4
Q

16.2

Define “Bronsted-Lowry base”.

A
  • Accepts a proton from another substance.
  • Doesn’t only apply to solutions.
  • Must have a pair of nonbonding electrons that can be used to bind the H+ ion
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5
Q

16.2

In the equation HCl(g) + H2O(ll) —> H3O+ + Cl-, what is the Bronsted-Lowry acid and what is the base?

A

The base is H2O. The acid is HCl.

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6
Q

16.2

Define “amphiprotic”.

A
  • Substance that can act as an acid or a base.
  • Acts as a base when combined w/ something more acidic than itself, and it acts as an acid when something more basic than itself.
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7
Q

16.2

Give It Some Thought - p. 670

In the forward reaction, which substance acts as the Bronsted-Lowry base:

HSO4- + NH3 SO4 2- + NH4 +

A

NH3 is the Bronsted-Lowry base.

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8
Q

16.2

In the equation HNO2 + H2O NO2- + H3O+, what are the conjugates?

A

NO2- is the conjugate base of HNO2.

H3O+ is the conjugate acid of H2O.

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9
Q

16.2

Give It Some Thought - p. 672

Using the three categories (strong, weak, negligible), specify the strength of HNO3 and the strength of its conjugate base, NO3-.

A

Strong, negligible.

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10
Q

16.2

In the equation HCl + H2O —> H3O+ + Cl-, where does the equilibrium lie?

A

It lies to the right because H2O’s conjugate base, H3O+, is stronger than HCl’s conjugate base, Cl-, so Cl- can’t take back the protons to become HCl again.

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11
Q

16.2

In the equation CH3COOH + H2O H3O+ + CH3COO-, where does the equilibrium lie?

A

To the left because CH3COO-, CH3COOH’s conjugate base, is stronger than H3O+, H2O’s conjugate base, and will accept the H+ more easily.

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12
Q

16.3

What is the autoionization of H2O?

A

H2O + H2O H3O+ + OH-

  • Extremely rapid in both directions
  • Only ~2/10^9 molecules are ionized at any given instant… so pure H2O is a bad conductor of electricity
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13
Q

16.3

What is the H2O equilibrium expression/equation?

A

Kw = [H3O+][OH-] = [H+][OH-]= 1.0 x 10^-14

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14
Q

16.4

What is the formula to find pH?

A

-log[H+]

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15
Q

16.4

Why do pHs generally have 2 decimal places?

A

Only the numbers to the right of the decimal point are the sig. figs. in a logarithm.

Ex: -log (1.0 x 10^-7) = -(-7.00) = 7.00

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16
Q

16.4

What is the formula to find pOH?

A

-log[OH-]

17
Q

16.4

How do pH & pOH correlate?

A

pH + pOH = 14.00

18
Q

16.5

What are the 8 strong acids?

A

HCl, HBr, HI, H2SO4, HClO3, HClO4, HNO3, HIO4

19
Q

16.5

What are the 7 strong bases?

A

Alkali metals + OH-, Ca(OH)2, Sr(OH)2, Ba(OH)2

20
Q

16.5

How do scientists use ionic metal oxides to form OH-?

A

The net ionic equation for these metal oxides + H2O is O2- + H2O —> 2 OH-, making a strong base.

21
Q

16.6

What is Ka, and what does it indicate?

A

Acid-dissociation constant. It shows the magnitude of an acid’s tendency to ionize in H2O. The larger the value of Ka, the stronger the acid.

22
Q

16.6

What is percent ionization?

A

Another measure of acid strength.The stronger the acid, the greater is the percent ionization.

(Concentration ionized/original concentration) x 100%

or

([H+]equilibrium/[HA]initial) x 100%

23
Q

16.6 - Give It Some Thought p. 685

When and why can we assume that the equilibrium concentration of a weak acid equals its initial concentration?

A

If Ka is x 10^-5 or less, this indicates that the equilibrium lies to the left, or to the reactants’ side, so any sort of change will be very small compared to the initial concentration.

If x is found to be >~5% of the intial concentration, however, the quadratic formula must be used.

24
Q

16.6

When does the percent ionization of a weak acid decrease?

A

When ionization increases.

So, for instance, doubling the concentration of a weak acid will not double the concentration of H+.

25
Q

16.6

What is a polyprotic acid?

A

It has more than one ionizable H atom, and thus two acid-dissociation constants. It is always easier to remove the 1st proton from a polyprotic acid than to remove the 2nd, due to electrostatic attractions.

H2SO3 HSO3- + H+ Ka1 = .017
HSO3 H+ + SO32- = 6.4 x 10^-8

26
Q

16.6

Where does equilibrium lie for the dissociation of H2SO4?

A

H2SO4 —-> HSO4- + H+

To the right because it dissociates completely.

HSO4- SO4 2- + H+

Still to the right because Ka2 is .012, and still quite large.

27
Q

16.6

How do you find the pH of polyprotic acids?

A

As long as Ka values differ by a factor of 10^3 or more, treat them as though they’re monoprotic. Most of the H+ will come from the 1st ionization reaction anyway.

28
Q

16.7

What is the base-dissociation constant?

A

Always refers to the equilibrium in which a base reacts with H2O to form the corresponding conjugate acid and OH-.

Ex.: NH3 + H2O NH4+ + OH-

[NH4+][OH-]/[NH3]

29
Q

16.7

What are the two general categories of weak bases?

A
  1. Neutral substances with an atom that has a nonbonding pair of electrons that can serve as a proton acceptor. Most contain N. These substances include NH3 & a related class of compounds called amines.
  2. Anions of weak acids. For example, ClO- from HClO.
30
Q

16.7

What is an amine?

A

In organic amines, 1+ N-H bonds in NH3 is replaced with a bond between N and C. So, the replacement of one N-H bond in NH3 with an N-CH3 bond produces NH2CH3, or methylamine.

31
Q

16.7

Give the chemical formula for the reaction of methylamine with water.

A

CH3NH2 + H2O CH3NH3+ + OH-

32
Q

16.8

What’s the relationship between Ka and Kb?

A

(Ka)(Kb) = Kw

Applies only to conjugate acid-base pairs.

33
Q

16.8

What are pKa and pKb?

A

-log Ka, -log Kb

pKa + pKb + pKw = 14.00

AP Chemistry (20 decks)

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