lecture 6

Question 1

Why does lemon juice sting in a cut?

Answer 1

there is a pH difference between the lemon which is more acidic and your blood which is more neutral

Question 2

How are acids and bases applicable to pharmaceutics?

Answer 2

We need to know the pH of drugs so that there is no pain due to a pH difference when the drug is administered

Question 3

Why doesnt diluting acid burn in eye with water not do much?

Answer 3

Water doesnt do much to acid. so there is still a pH difference which is what causes the pain in your eye

Question 4

Why do cleansers feel soapy and slippery?

Answer 4

Bases dissolve a bit of the outside layer of your skin

Question 5

What do acids liberate on dissociation?

Answer 5

H+ ions

Question 6

What do bases supply on dissociation?

Answer 6

OH- ions

Question 7

What theory of acids and bases do we most commonly use?

Answer 7

the brownsted lowry theory

Question 8

What are acids?

Answer 8

proton donators

Question 9

what are bases?

Answer 9

proton acceptors

Question 10

what are amphiprotic substances?

Answer 10

things that can both donate and accept protons

Question 11

what are aprotic substances?

Answer 11

things which dont want to give or take protons

Question 12

In the lewis theory aka electronic theory, what is an acid?

Answer 12

a molecule or ion that accepts an electron pair to form a covalent bond

Question 13

in the lewis theory aka electronic theory what is a base?

Answer 13

a substance that provides the pair of electrons to form that covalent bond

Question 14

What are the physical textures of acids and bases?

Answer 14

acids taste sour, and produce H3O+

bases feel slippery and soapy. When they react with acids, a salt is formed

Question 15

What is equilibrium?

Answer 15

the balance between 2 opposing forces or reactions. This equilbrium is dynamic i.e. moves forwards and backwards, not completely still

Question 16

What do strong acids do?

Answer 16

dissociate completely

Question 17

what do weak acids do?

Answer 17

dissociate partially and are slightly soluble

Question 18

Why is water not included in our equilbrium constant?

Answer 18

because we know the concentration of water stays the same essentially, until we get to really concentrated solutions

Question 19

Why can we exchange the H3O+ with A-?

Answer 19

the concentrations are equal (the molar ratio of the equation is 1)

Question 20

what are the log rules?

Answer 20

log(a/b) = log a - logb

log a ^n = n x log a

Question 21

What is pKa?

Answer 21

the -log of Ka.
it tells us how dissociative a molecule is at a certain pH

this can tell us whether a drug will be ionised or unionised which determines where it can be absorbed in the body

Question 22

What are indicators?

Answer 22

an acid conjugated base pair.
They indicate what the pH is.
They have an unionised colour and an ionised colour.

Question 23

what is universal indicator?

Answer 23

a combination of indicators so it gives us a different colour for each pH

Question 24

What is the pka of the indicator?

Answer 24

the pH at which the indicator changes from its unionised to its ionised form i.e. where it changes colour

Question 25

what is a buffer?

Answer 25

solutions which contain an acid and its conjugate base or vice versa which resist the change of pH

Question 26

Is an indicator a type of buffer?

Answer 26

yes

Question 27

How is the derivation of the henderson hasselbach equation achieved?

Answer 27

work out Ka.
-logKa and fraction
As H3O+ and A- are multipled, they are a plus (when divided they are negative)

Take the negative into the bracket by chnging the sign of everything inside the bracket

Move everything to oneside apart from -logH3O+

use log rules to recombine everything and end up with henderson hasselbach equation

Question 28

Which buffers are common? which are uncommon?

Answer 28

Common buffers are weak acids and salts

buffers from weak bases and salts are uncommon

Question 29

What happens when you dilute a buffer?

Answer 29

pure act of dilution does not change pH, but it does change its buffering ability

Question 30

Why do we use acidic buffers?

Answer 30

Temperature as a specific effect on basic buffers, a lot worse than for acidic buffers.

Question 31

Can a drug be a buffer?

Answer 31

yes. Buffers do not have to be something we add extra to.

e. g. salicylate acid. We can trn it into acetyl salicyclic acid which is aspirin

Question 32

What is the buffer capacity/strength of a buffer?

Answer 32

the ability of the buffer to resist pH changes
this is also known as its proficiency or index
Given by the equation β= ΔB/ΔpH

Question 33

How is buffer capacity measured?

Answer 33

we can add a little bit of acid and base and see how much the pH changes

if we add a lot of acid/base and it doesnt change much then it has a high buffering capacity

Question 34

What is the buffering capacity of water?

Answer 34

water has almost no buffering capacity

Question 35

What kinds of biological buffers are there?

Answer 35

Our bodies also have buffers so that we can resist changes in pH
Our blood is kept between pH 7.35-7.45 as if it goes too much out of this range, we would die.

We also have a good buffer in our eyes so a drop of lemon juice doesnt damage our eyes

There is lso CO2 and bicarbonate in the blood. If we dont breath enough Oxygen, CO2 accumulates causing the blood to become more acidic. Ventilating the patients will decrease the CO2 and hence, the activity

Likewise if someone hyperventialtes, they reduce too much of their CO2 so the blood becomes basic.
This is why you get them to breathe into a paper bag to slowly return CO2 levels back to normal

Question 36

What kinds of pharmaceutical buffers are there?

Answer 36

Eyedrops, and injections dont steam when administered because the pH has been buffered to the right level for your body

Changing pH can also increase solubilty of various drugs

Question 37

What can you do if you want to give a water based solution to a patient which can be ionised but is not very soluble?

Answer 37

You can shift it towards its ionised form by changing the pH of the environment so that it can dissolve in water.

Question 38

Where else are buffers used?

Answer 38

in analytical tests for determination

Question 39

what is another pharmaceutical application of pH and drugs? (paracetemol)

Answer 39

Paracetemol can be tasted if in solution and bit into. This is very bitter and unpleasant
In a suspension form, we wont taste it as it is solid.

The pH is manipulated to maintain it in a solid form in the suspension
we also have to maintain the tonicity (how salty it is) as it must have an equal osmotic pressure with respect to the membrane it comes into contact with.

Question 40

Why is the tonicity of the drug importnat?

Answer 40

membranes should not be exposed to the wrong tonicity and likewise we dont want to inject something of the wrong tonicity into your body.

The lining of all blood vessels are lined with endothelial cells (which are leaky) so these will be affected as well

Question 41

What is the significance of pKa?

Answer 41

pKa tells us that a certain pH, how much of the drug will be ionised
At any one pH, if we know the pKa we can predict how much is ionised and how much is unionised,
The ionised drug is more water based
Unionised form of drug is more lipidphilic
The unionised form will be more readily absorbed