LEC1: pH and Buffers Flashcards Preview

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Flashcards in LEC1: pH and Buffers Deck (36):

where can a buffer be useful?

+/- 1 pH unit around the pKa


formula for dissociation constant of an acid?

A image thumb

how do weak acids/abses act as buffers?

weak acids & bases only partially dissociate into charged species 
buffers provide a reservoir of acid that consumes added base, reservoir of base that consumes added acid 
therefore dampen pH changes 


what do acids and bases tend to do, what is each's effect on pH? 

acids donate protons, cause a decrease in pH
bases accept protons, cause an increase in pH by removing protons from H2O


what do acids/bases each do re: proton exchange? 

acids donate protons 
bases accept protons


what is pH for pure water under normal conditions? 

pH = 7


what is the definition of pH? 

pH = -log[H+]

pH is the measure of the Hion concentration


what is the effect of buffers on pH? 

buffers dampen pH changes


what is the Ka?

dissociation constant of an acid


what does this curve show? 

Q image thumb

concentration curve for buffer 

shows relationship between acid added/base added (x axis) & pH (y axis)

see small changes to pH when add base (to the R) or acid (to the L) because this is where buffer is useful 

see if add a LOT of base or acid, the conjugate acid/base is exhausted, buffer is no longer useful as a buffer 


what is Henderson-Hasselbach equation? 

A image thumb

what is the pKa of a weak acid?

the pH at which 1/2 of the molecules are dissociated into ions


what is the maximum buffering capacity of a weak acid?

1 pH unit above/below the pKa 

here, both acid and conjugate base are present, can consume added ions 


how is an acid and a base when each is above its pKa?

acid above its pka: unprotonated, charged 

base above its pKa: unprotonated, neutral


what buffers human blood?

bicarbonate buffering system


what is the Henderson-Hasselbach equation for the formation of bicarbonate?

A image thumb

what does this graph represent? 


Q image thumb

titration curve of carbonic acid/bicarbonate system 

pH = 6.1 is known neutral state; see that between pH=5.1-7.1, small changes in pH



what is the pH of blood? 



at physiologic pH of blood, what is ratio of bicarbonate:carbonic acid? explain

[H2CO3] to [HCO3-] is 1:20 

physiological mechanisms can regulate this concentration

1) [H2CO3] modulates with breathing rate, affecting COlevels in the blood - rxn becomes more acidic

2) [HCO3-] modulates by changing the rate of its elimination by the kidney - rxn becomes more basic


when does a drug get absorbed?

if a drug is a weak acid, aka protonated & uncharged, it can be absorbed into the stomach 



describe how aspirin works, the form its found in in the stomach

pH of the stomach = 1.5 

aspirin is a weak acid, pH= 3.5

therefore at pH = 1.5, aspirin will be protonated and uncharged, and therefore can cross membrane > stomach & intestines

protonated form is 100x more abundant than charged form 


what is charge of each part of an amino acid? & what is amino acid's charged at pH=7?

weakly basic amino group, pKa = 9-10 

weakly acidic carboxyl group, pKa = 2

overall, at pH=7, charge of an amino acid=0


structure of an amino acid?

A image thumb

what does it mean that amino acids are optical isomers?

their stereoisomers are nonsuperimposable mirror images


what is the simplest amino acid? how is it found in nature?

glycine; R group = H

overall charge is positive, both groups are protonated, if in highly acidic environment

overall charge is neutral in physiologic form (normal!)

overall charge is negativeboth groups are unprotonated, if in highly basic environment


what is this? explain what is happening


Q image thumb

represents the acidic/basic propteries of an amino acid w/ an uncharged R-group, aka glycine

see 2 regions where it behaves as a buffer:

1) pK1, the pKa of carboxyl group 

2) pK2, the pKa of the amino group



what is the isoelectric point?

the pH in which the amino acid is electrically neutral - charges balance


what is the pI of amino acids w/ R groups that cannot be ionized?



how are amino acids re: protonation, charge, at physiological pH?

carboxyl group is unprotonated, negative charged

amino group is protonated, positively charged


how does the body control the level of CO2 in blood?

[H2CO3] modulates with breathing rate, affecting CO2 levels in the blood 

Henderson-Hasselbalch rxn becomes more acidic



how does the body control bicarbonate concentration?

 [HCO3-] modulates by changing the rate of its elimination by the kidney

H-H rxn becomes more basic


how does a buffer reduce the effect of added acid or base on the pH of a solution?

buffers dampen pH changes by providing a reservoir of acid that consumes added base / a reservoir of base that consumes added acid 

at +/- 1 pH unit above or below a weak acid's pKa, added ions are consumed by buffer


why is the maximum buffering capacity of a weak acid at +/- 1 pH unit of its pKa?

because in this pH range both the acid and its conjugate base are present and can consume the added ions 



is a weak acid charged or uncharged at 2 pH units above its pKa?



is a weak base charged or uncharged at 2 pH units above its pKa?



why is the carbonic acid/bicarbonate system an effective buffer of blood even though its combined pKa is more than 1 more pH unit below that of blood pH?

the combined pKa of carbonic acid/bicarbonate = 6.1 

blood pH=7.4

works b/c components can be regulated by physiological mechanisms

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