Flashcards in lecture 6 Deck (41)
Why does lemon juice sting in a cut?
there is a pH difference between the lemon which is more acidic and your blood which is more neutral
How are acids and bases applicable to pharmaceutics?
We need to know the pH of drugs so that there is no pain due to a pH difference when the drug is administered
Why doesnt diluting acid burn in eye with water not do much?
Water doesnt do much to acid. so there is still a pH difference which is what causes the pain in your eye
Why do cleansers feel soapy and slippery?
Bases dissolve a bit of the outside layer of your skin
What do acids liberate on dissociation?
What do bases supply on dissociation?
What theory of acids and bases do we most commonly use?
the brownsted lowry theory
What are acids?
what are bases?
what are amphiprotic substances?
things that can both donate and accept protons
what are aprotic substances?
things which dont want to give or take protons
In the lewis theory aka electronic theory, what is an acid?
a molecule or ion that accepts an electron pair to form a covalent bond
in the lewis theory aka electronic theory what is a base?
a substance that provides the pair of electrons to form that covalent bond
What are the physical textures of acids and bases?
acids taste sour, and produce H3O+
bases feel slippery and soapy. When they react with acids, a salt is formed
What is equilibrium?
the balance between 2 opposing forces or reactions. This equilbrium is dynamic i.e. moves forwards and backwards, not completely still
What do strong acids do?
what do weak acids do?
dissociate partially and are slightly soluble
Why is water not included in our equilbrium constant?
because we know the concentration of water stays the same essentially, until we get to really concentrated solutions
Why can we exchange the H3O+ with A-?
the concentrations are equal (the molar ratio of the equation is 1)
what are the log rules?
log(a/b) = log a - logb
log a ^n = n x log a
What is pKa?
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
What are indicators?
an acid conjugated base pair.
They indicate what the pH is.
They have an unionised colour and an ionised colour.
what is universal indicator?
a combination of indicators so it gives us a different colour for each pH
What is the pka of the indicator?
the pH at which the indicator changes from its unionised to its ionised form i.e. where it changes colour
what is a buffer?
solutions which contain an acid and its conjugate base or vice versa which resist the change of pH
Is an indicator a type of buffer?
How is the derivation of the henderson hasselbach equation achieved?
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
Which buffers are common? which are uncommon?
Common buffers are weak acids and salts
buffers from weak bases and salts are uncommon
What happens when you dilute a buffer?
pure act of dilution does not change pH, but it does change its buffering ability
Why do we use acidic buffers?
Temperature as a specific effect on basic buffers, a lot worse than for acidic buffers.
Can a drug be a buffer?
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
What is the buffer capacity/strength of a buffer?
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
How is buffer capacity measured?
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
What is the buffering capacity of water?
water has almost no buffering capacity
What kinds of biological buffers are there?
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
What kinds of pharmaceutical buffers are there?
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
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?
You can shift it towards its ionised form by changing the pH of the environment so that it can dissolve in water.
Where else are buffers used?
in analytical tests for determination
what is another pharmaceutical application of pH and drugs? (paracetemol)
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.
Why is the tonicity of the drug importnat?
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