Ceutics Exam 2

Weak acid and weak base is dependent on the intrinsic acidity/basicity (pka) of the molecule and the pH of the environment

Extent of ionization

Weak acids ______ a proton

donate

Weak bases _____ a proton

accept

_____ is a hydrogen atom that has lost an electron

[H+]

This equation provides a means to determine the impact of the solution/environment pH and the drug pKa on the degree of ionization

HH equation

the solution pH at which weak electrolyte is 50% ionized and 50% unionized

pKa

A lower pka = _______acid

stronger

a higher pka= ______ base

stronger 

True or false: pKa does mean weak acid

FALSE

the _____ the pka, the _____ [H+] dissociation from the HA form and the ____ the [H+] attracting strength of the A- form

smaller, greater, lesser

the ____ the pKa, the ____ [H+] dissociation from the BH+ form and the _____ the [H+] attracting strength of the B form

larger, less, greater

Weak acids are given a single name followed by what suffix

-ium or acid 

A weak acid with an ester with the ending -ium then -ate

defining an ester

A weak base has the suffix

-ate or -ide

True or false: weak bases are generally one word

false;two

For ionizable drugs, absorbed dose is determined by the extent of unionized form at given pH

pH partition hypothesis

The more lipid soluble form of a drug can permeate

the cell membrane

What is the cell membrane primarily composed of

• phospholipids

• cholesterol

The cell membrane is

• lipophilic

• hydrophobic

drugs which are unionized or relatively non-polar can be “dissolved” in the hydrophobic cell membrane which means they can

move and partition

in a low pH environment, what is [H+] (acidic drug)

high

in a low pH environment, [HA] (increases/decreases) (acidic drug)

increases

in a low pH environment, drug absorption (increases/decreases) (acidic drug)

increases

in a high pH environment (acidic drug) the [H+] is (high/low)

low

in a high pH environment (acidic drug), [A-] (increases/decreases)

increases

in a high pH environment (acidic drug), drug absorption (increases/decreases)

decreases

(basic drug): in a low pH, [H+] is (high/low)

high

(basic drug): in a low pH. [BH+] (increases/decreases)

increases

(basic drug): in a low pH, drug absorption (increases/decreases)

decreases

(basic drug): in a high pH, [H+] is (high or low)

low(basic drug): in a high pH

(basic drug): in a high pH, [B] (increases/decreases)

increases

(basic drug): in a high pH, drug absorption (increases/decreases)

increases

A drug in its ionic form is more readily _____ in polar solvents compared to its _____ form

soluble, un-ionized

the extent of drug ionization of a weak base or acid is dependent on the ______ and the ______-

• pH of the solution

• pKa of the drug

What type of solubility will be affected by the pH of the solution and the pKa of the drug

aqueous

When predicting solubility, we assume that

• ionized form is infinitely soluble compared to the unionized form

Solubility of unionized form in the absence of ionized form

intrinsic solubility

-ide, -ate drug may ppt. with

-ium, -ium -ate

-ide, -ate may ppt. as B with

increasing or higher pH

-ium, -ate may ppt as HA with 

decreasing or lower pH

How do we lower pH of weak electrolyte drug solution

add strong acid

how do we raise pH of weak electrolyte drug solution

add strong base

A salt formation of weak base + strong acid yield pH (</>) 7.0 solution

pH < 7.0

A salt formation of weak acid + strong base yield pH (</>) 7.0 solution

pH > 7.0 solution 

what happens when you combine a weak acid and weak base

• forms weak electrolyte salts that ionize

a weak acid with a weak base forms equal molar species and dissolution of salt form which yields

variable pH depending on pKa of either HA or B species

compounds, or mixtures of compounds which, by their presence in solution, provide resistance to any drastic pH change when small amounts of acid or alkali are added or generated

buffer

Why use buffers?

• drug salts can impart acidity or basicity in unbuffered solutions

• provide an appropriate environment to preserve the desired solubility and stability of the drug

the ability of a buffer to withstand the effects us expressed in terms of

buffer capacity

how does the ratio of ionized to unionized species become significant

if large amountsare of acid or base is added to a buffer solution

buffer capacity is the ratio of the amount (moles) to [H+] or OH- required to change the pH of 1 liter of the buffer by 1 pH unit

Van slyke definition

the (higher/lower) value of B indicates a better buffer capacity

higher because a larger amount of acid or base is needed to cause unit change in pH

factors that influence buffer capacity

1. magnitude of individual concentrations of the buffer components 

2. value of the salt/acid ratio

incrased concentrations of buffer components results in a ____ buffer capcity

greater

B increases as the ratio approaches _____

unity 

Homogenous mixture of two or more components that form a single phase

Solution

Homogenous, physically distinct portion of a system that is separated from the other portions by bounding surfaces

Phase

This determines the phase of the system

Solvent

Dispersed molecules or ions within the solvent

Solute

Liquid solute in liquid solvent example

Alcohol in water

Solid in liquid example

Salt in water

Solid in gas example

Iodine in O2

Liquid solute in solid solvent

Oil in wax

Gas solute in solid solvent

Hydrogen in metal

Solutes forming a true solution can be classified as

• electrolytes

• Non-electrolytes

Forms ions in solution- ionize and conduct electricity

Electrolytes

Concentrated aqueous preparations of sugar

Syrups

Sweetened hydroalcoholic solutions

Elixirs

Alcoholic or hydroalcholic solutions

Tinctures

Conveys the amount of solute relative to the amount of either solvent or solution

Concentration

Qualitative properties of concentration include

Dilute/weak or concentrated/strong

Property or characteristics of a solution that depends on the number, not nature of the solute dissolved in the solvent to form a solution

Colligative properties

Examples of colligative properties

• vapor pressure

• Freezing point

• Boiling point

• Osmotic pressure

The values of colligative properties for electrolytes would be expected to be (greater/lesser) than that of a non-electrolyte at similar concentrations due to number of ions formed after dissolution

Greater

When a solid or liquid evaporates to a gas in a closed container, the rate of condensation of the gas becomes _____ to the rate of evaporation of the liquid or solid

Equal

Pressure exerted by the gas in equilibrium with a solid or liquid in a closed container at a given temperature is

Vapor pressure

Sum of all partial pressures of each volatile components

Ideal solution

This is equal to the vapor pressure of the pure constituent multiplied by its mole fraction in a solution

Partial pressure

The temperature at which the vapor pressure of a liquid is equal to atmospheric pressure

Boiling point

When solutes are dissolved in a solvent, the boiling point of the solvent is _____

Elevated

Elevation of the boiling temp is (directly/indirectly) related to the molality of the solute in the solution

Directly

what reduces vapor pressure

Additional of solute

What happens when solute is added to freezing solid

Depresses freezing point

Depression of freezing point of the solution is (directly/indirectly) related to molality of the solute in the solution

Directly

Passage of the solvent into a solution through a semi-permeable membrane from a dilute solution to a concentrated one

Osmosis

What is the goal of osmotic pressure

Establish equal concentration

Tonicity reflects what

Reflects a biological membrane

Hypertonic

Higher concentration on the outside of the cell relative to the inside, cell shrinks

Hypotonic

Low concentration on the outside relative to the inside, cell swells

Cells shrink

Crenation

Cell swells

Lysis

Unit or measure that defines the number of moles of a chemical compound that contribute to a solution’s osmotic pressure

Osmole

Measure of the osmoles of solute per liter (L) of solution

Osmolarity

Measure if the osmoles of solute per kg of solvent

Osmolality

Freezing point is (directly/indirectly) related to tonicity

Directly

Van Hoff factor