PH

Question 1

What does acid contain a lot of?

Answer 1

Hydrogen ions (H+)

Question 2

If a base is soluble what does it mean?

Answer 2

It means it is alkali and has a small number of hydrogen ions

Question 3

What do we use to measure the acidity of a solution?

Answer 3

A pH scale

Question 4

What is meant by a ‘Bronsted acid’?

Answer 4

Proton donor

Question 5

What is meant by a ‘Bronsted base’?

Answer 5

Proton acceptor

Question 6

What is a ‘Lewis Acid’?

Answer 6

Electron pair acceptor e.g all metal cations

Question 7

What is a ‘Lewis base’?

Answer 7

Electron pair donor

Question 8

What is conjugate acid-base pairs?

Answer 8

Every acid has a conjugate base and every base has a conjugate acid

Question 9

What are the two ways to measure pH?

Answer 9

1.) Acid base indicator- changes colour in specific pH ranges, can have different colours in their acid or conjugate base forms

Question 10

What are strong and weak acids?

Answer 10

90% of drugs are weak acids or bases

If the hydrogens are fixed quite firmly onto the structure it is not going to be a strong acid.

If the hydrogens are able to separate then it will lead to the acid becoming stronger since they will separate and go into the solution.
The solubility of a compound depends on how strong or weak the acid/base of the drug structure is.

Question 11

Strong acids

Answer 11

Almost completely dissociated into ions e.g. HCl
HA—-> H+ + A-

Question 12

Weak acids

Answer 12

Partially dissociated into ions e.g. acetic acid
HA <—-> H+ + A-

Question 13

What makes an acid strong?

Answer 13

-solvent effects
-energetic stability
-the nature of the parent molecule
-the strength of the HA bond

Question 14

What are logarithms?

Answer 14

Converts a large range of values into a small range
Log10= 1
Log100= 2
Log1000= 3

Question 15

What are monophonic and polyphonic acids?

Answer 15

Monoprotic- lose one proton per molecule of acid e.g; HCl
Diprotic- lose two protons per molecule e.g; H2SO4

Question 16

What is a buffer?

Answer 16

Keeps the pH approximately constant when small amounts of acid or alkali are added

Question 17

Tell me more about a buffer:

Answer 17

*effects are suppressed with enough dilution
*buffer capacity is a measure of the resistance to pH change
*buffer capacity is at a maximum when the pH of the buffer is equal to the pKa of the weak acid
*decreases as the pH extends more than one unit either side of this value
*abundant supply of A- ions to remove H+ from acid added
*HA can supply H+ to react with any strong base added

Question 18

What is the buffering of blood?

Answer 18

-3 diff blood buffer systems that hold the pH at 7.40
-blood has a much greater capacity for absorbing acidic ions than for basic ions

Question 19

What is pH partition theory?

Answer 19

A drug must cross the plasma membrane therefore it must be lipid soluble. Since most drugs are weak electrolytes, has to be expected that unionised form of acids and bases e.g. the lipid soluble species will diffuse across while the ionised form will be rejected
^ partioning has a pH dependence
-extent of ionisation of a drug has an important effect on; it’s absorption, distribution and elimination

Question 20

What are the limitations of the pH theory?

Answer 20

-calculations; equilibrium distribution is attained
-stomach and blood are not closed= equilibrium will rarely be achieved (static compartments)
-drug is removed from the stomach to the intestine by stomach contractions
-drug entering the blood is removed from the site of absorption by circulation and then distributed into tissues.
^however, absorption from the stomach using direct measurements = qualitative hypothesis