Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

Pharmaceutics > Ionic Equilbria > Flashcards

Ionic Equilbria Flashcards

1
Q

Describe Acids and Bases by Arrhenius

A

Acids: substances that contain hydrogen and can dissolve in water to release H into solution

HCl + H2O  H+(aq) + Cl-(aq)

Bases: Substances that dissolve in water to release hydroxide ions (OH-) into solution

NaOH + H2O  Na+(aq) + OH-(aq)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Show the introduction of theories for acid base

A

Arrhenius’ classification – In aqueous solutions:

  • *Acid** yields hydrogen ion: HA  H+ + A-
  • *Base** yields hydroxyl ion: BOH  B+ + OH-
  • *Bronsted-Lowry Theory (“proton theory”), 1923**
  • *Acid** tends to give out proton: proton donor
  • *Base** tends to accept proton: proton acceptor

Lewis Electronic Theory (“electronic” theory), 1923
Acid accepts an electron pair to form a covalent bond
Base provide an electron pair to form a covalent bond
H+ + OH-  H2O

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is the bronsted lowry concept?

A

Acid + Base Conjugate acid + Conjugate base

Conjugate acid = molecule or ion created when the base accepts the proton (conjugate acid-base pair)

Conjugate base = molecule or ion remaining after the eacid has lost a proton

Reaction can proceed in either forward or backward direction; in each case the acid donates a proton to the base

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Describe Acid - Base Equilibrium

A

When strong acids are dissolved in water, complete dissociation occurs

When weak acids are dissolved in water, they dissociate only

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is Sorensen’s definition for pH

A

Definition:

   pH ( “ pH+ ”) = - log [“ H+ ”] = - log [H3O+] =

“pX”: -log10X (- “logX”) —- negative common logarithm
For pure water, pH = -log [H+] = -log (1 x 10-7) = 7

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Describe the pH scale?

A

Acids pH < 7

Bases pH > 7

Neutral pH = 7

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Describe the ionization of water?

A
  • Water can be both (very very.. WEAK) base and acid
  • Other H2O acts as an acid and loses H+ to become OH-
  • One H2O acts as a base and gains H+
  • H3O+: hydronium (solvated ion), H+ is used as a symbol of H3O+ for simplicity
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is Kw defined as? (Kw= ionic product of water)

A

Kw = k [H2O]2 = [H3O+][OH-]

At 25C, Kw = 10-14 (mol/L)2 = [H3O+][OH-] = 10-7 · 10-7

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Describe Ionization of weak acids?

A

Define Ka for acid HA at acid-base equilibrium —

HA + H2O  H3O+ + A-
HA  H+ + A-

Ka = [H+][A-] / [HA]

Ka is the ionization constant of a weak acid HA (acidity constant, or dissociation constant of HA) Units mol/L

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the pKa of a weak acid?

A

Ka = [H+][A-]/[HA]

pKa = - logKa
The stronger an acid, the smaller its pKa.
Ionization constants are used to measure the strength of acids and bases and calculate the extent of ionization, such as Ka and pKa, Kb, pKb

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Describe the ionization of weak bases?

A

Define Kb for a base B at acid-base equilibrium —

NH3 + H2O  NH4+ + OH-
B + H2O  BH+ + OH-

Kb: base ionization constant (basicity constant)
Kb = [BH+][OH-]/[B]

For water solution only contains B, BH+, and OH-
[BH+] = [OH-]
[OH-]2 = Kb[B]

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the pKa of a weak base?

A

Define: the Ka of the base B is the Ka of its conjugate acid BH+. For its conjugate acid BH+, at equilibrium, the acidity constant of BH+ is Ka

NH3 + H2O  NH4+ + OH-
B + H2O  BH+ + OH-
BH+ Ka H+ + B
Ka = [H+][B] / [BH+]
pKa = - log Ka

The stronger a base, the higher its pKa.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

pKa and pKb

A

pKa + pKb = 14
pOH + pH = 14

Kb is less and less used in pharmacy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the ionization of ampholytes?

A

Most polyprotic acid systems are amphoteric systems (Except HnA and An-)
Ionization of amphoteric electrolytes
Amphoteric electrolyte (or ampholyte): A specie can function either as an acid or a base.
Ampholytes often are molecules contain both acidic and basic functional groups, which will act as acids under certain conditions, and act as bases under certain other conditions. Examples: amino acid, proteins

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is a zwitterion form and isoelectric point?

A
  • *Zwitterion:** Amphoteric species that carry both positive and negative charges and the whole molecule is electrically neutral.
  • *Isoelectric point (pI):** the pH at which the zwitterion forms and the net charge of the ions equal zero.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is a salt?

A
  • A salt is the combination of an anion (- ion) and a cation (+ ion)
  • An acid + A base => A salt
  • In a solid salt, the ions are held together by the difference in charge
  • If a salt dissolves in water, it usually dissociates to form ions
  • The reaction of anions or cation of the salt with water to produce acidic or alkaline solution is called hydrolysis NaCl
  • Solutions containing a salt of a strong acid and a strong base (SASB)
  • Nacl
  • Solutions containing a salt of a weak acid and a strong base (WASB)
  • NH4 Cl
  • Solutions containing a salt of a strong acid and a weak base (SAWB)
  • NH4 Ac
  • Solutions containing a salt of a weak acid and a weak base (WAWB)
17
Q

A solution with a salt of a strong acid and a strong base

A

The solution is neutral, pH = 7
Neither the cation or the anion undergoes hydrolysis

18
Q

A salt of a weak acid and a strong base

A

Basic pH

pH = ½(pKw + pKa + log[A-])

19
Q

A salt of a strong acid and a weak base

A

Acidic pH

pH = ½( pKa - log[BH+])

20
Q

A salt of a weak acid and a weak base

A

Can be acidic, neutral, or basic

21
Q

What is the importance of ionic equilibria in pharmaceutical science?

A

Many drugs and ingredients are organic weak electrolytes.
Weak electrolyte can exist in an ionized form and an unionized form
The degree of ionization directly affects drug physicochemical properties, such as solubility, hydrophobicity, stability, etc.
The degree of ionization directly affects drug dissolution, absorption, transportation, and excretion.
Ionized forms are more water-soluble and less lipophilic
Unionized forms are less water-soluble but more lipophilic, and more permeable to lipid membrane
pH partition hypothesis for drug absorption: the absorption of a weak electrolyte is determined mainly by its existing unionized form at the site of absorption, when drug are absorbed from the GI tract by passive diffusion. (page 238)

22
Q

The SUMMARY

A
  1. Ionization of water
  2. Ionization of strong acids or strong base (SA, SB) pH = -log[H+]
  3. Ionization of weak acids (WA) pH = ½ (pKa – log [HA])
  4. Ionization of weak bases (WB) pH = ½ (14 + pKa + log [B])
  5. Ionization of polyprotic electrolytes
  6. Ionization of ampholytes
  7. Ionization of salts
  • Solutions containing a salt of a strong acid and a strong base (SASB)pH= 7
  • Solutions containing a salt of a weak acid and a strong base (WASB)pH = ½ ( 14+pKa+log[a-])
  • Solutions containing a salt of a strong acid and a weak base (SAWB)pH = ½ ( pKa – log [BH+])
  • Solutions containing a salt of a weak acid and a weak base (WAWB)

Pharmaceutics (7 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions