Ioe Ph And Buffers

Front 1

Weak acids like acetic acid do not completely.....

Back 1

Weak acids like acetic acid do not completely ionise (dissociate) in water

Front 2

The equilibrium
reaction is:

Back 2

CH3COOH>>>>>CH3COO- H+

Front 3

The equilibrium constant (acid dissociation constant Ka) is given by:

Back 3

Ka= [h+][ch3coo-]
[ch3cooh]

Front 4

just like with hydrogen ion concentrations
and pH it’s convenient to express Ka values on a log scale as

Back 4

Pka values

Front 5

ph and pka are measures of?

Back 5

pH is a measure of acidity; pKa is a measure of the degree of dissociation:

Front 6

what would a

large pka

small pka mean

Back 6

Small pKa (large Ka) = dissociated to large extent – strong acid


Large pKa (small Ka) = dissociated to small extent – weak acid

Front 7

what is the formulae for PH ,

Back 7

PH= pKa + log proton acceptor ,
proton donor

Front 8

how is pka found

Back 8

by titration

Front 9

what is a buffer

Back 9

Buffers are molecules that resist pH changes that would otherwise occur by the small additions of acid or base to a system.

Front 10

Buffers cannot completely stop

Back 10

the pH changing – they reduce the change in pH that would otherwise occur in their absence

Front 11

Buffers are usually mixtures of

Back 11

mixtures of weak acids and their conjugate bases or weak bases and their conjugate acids.

Front 12

Acetic acid is monoprotic
so there is only one

Back 12

Acetic acid is monoprotic
so there is only one buffering
region 1 pH unit either side
of pH 4.8.

Front 13

The buffering region extend
about

Back 13

The buffering region extend
about 1 pH unit either side of
the pKa value (general rule)

Front 14

In the 3 plateau regions large additions of hydroxide only cause

Back 14

In the 3 plateau regions large additions of hydroxide only cause a small increase in pH

Front 15

These buffering regions extend
about

Back 15

These buffering regions extend
about 1 pH unit either side of
the pKa value (general rule)

Front 16

High concentrations of buffer components allow the buffer to handle?

what is high?

Back 16

High concentrations of buffer components allow the buffer to handle large additions of acid
or base – i.e. the buffering capacity is high

Front 17

the conjugate base
buffer component is bigger than
the acid component so this buffer would be more...

Back 17

when the conjugate base
buffer component is bigger than
the acid component so this
buffer would be more effective
at buffering added acid

Front 18

if the acid buffer
component is bigger than the
conjugate base component so
this buffer would be more
effective

Back 18

at buffering added base

Front 19

Buffer solutions have their own

Back 19

inherent ph

Front 20

this inherent ph depends on

Back 20

This depends on the ratio of acid component
to the conjugate base component and the dissociation characteristics of the buffer.

Front 21

in the hendle hesslebach equation what dose


ph stand for


pka stand for

a-/ha stand for

Back 21

ph stands for ph of the buffer


pka stands for - pka defining dissociation characteristics

A-/HA stands for the term defining ratio of a- to ha

Front 22

Animals strive to maintain

Back 22

to maintain intra and extracellular pH close to 7.4.

Front 23

A deviation of
1 pH unit would be

Back 23

catastrophic

Front 24

why is acidosis a bigger threat

Back 24

Acidosis is a bigger threat than alkalosis since we all
produce various acids through metabolic processes.

Front 25

Intacellular pH is largely buffered by

Back 25

buffered by phosphate and the histidine side chains of proteins

Front 26

histidine is the only

Back 26

Histidine is the only amino acid with a
pKa value near physiological pH

Front 27

Extracellular pH is buffered by

Back 27

the bicarbonate buffer system (phosphate and proteins also contribute a little):

Front 28

CO2 generated by the tissues dissolves in the

Back 28

the plasma

Front 29

This CO2(d) is in equilibrium
with carbonic acid which in turn is in equilibrium with

Back 29

bicarbonate

Front 30

what effect would an increase in h+ have


write out the equation from paper to mark

Back 30

If H+ increases the equilibrium is driven to the left which increases the concentration of
dissolved CO2. The increase in pCO2 causes excess CO2 to be lost through the lungs to the atmosphere.

Front 31

what effect would an increase in oh- have

write out the equation from paper to mark

Back 31

If H+ increases the equilibrium is driven to the left which increases the concentration of
dissolved CO2. The increase in pCO2 causes excess CO2 to be lost through the lungs to the atmosphere.

Front 32

In the mouth salivary buffering is vital in order to prevent

Back 32

dissolution of the tooth surface. Enamel is composed of substituted hydroxyapatite which will be in equilibrium with its constituent ions in saliva:

Front 33

write the equilibrium equation for hydroxyapatite

Back 33

Ca10(PO4)6OH2 >>>> 10Ca2+ + 6PO43- + 2OH-
<<<<<

Front 34

Impaired salivary output (xerostomia or dry mouth) leaves patients

Back 34

very susceptible to caries. Caused by many factors e.g. radiation therapy, some drugs, diseases (e.g. Sjogren’s syndrome, HIV), dehydration etc.

Front 35

what does le chateliers principle predict

Back 35

Le Chatelier’s principle predicts that protons (acid) removing hydroxide and phosphate from the right of the equation will drive more hydroxyapatite into solution (dissolve the teeth).
Salivary buffering is vital to oral health.

Front 36

There are 3 buffer systems in saliva:

Back 36

Bicarbonate (most important)
Phosphate
Proteins

Front 37

what is the big difference in salivary bicarbonate buffer system in saliva

Back 37

Saliva contains the enzyme carbonic anhydrase that catalyses
the uptake of the proton to bicarbonate which increases the efficiency of this
system.

Front 38

where is carbonic anhydrase retained

Back 38

Carbonic anhyrdrase VI is retained in pellicle

Front 39

Protons are not just buffered

Back 39

Protons are not just buffered – they are eliminated

Front 40

Plaque acid is produced by

which is the basis of

Acid levels can also increase due to

Back 40

Plaque acid is produced by bacteria fermenting dietary carbohydrate

cariogenesis


due to consumption of acidic foods
and drinks which can lead to dental erosion.

Front 41

what effect does mechanical stimulation have

Back 41

Mechanical stimulation associated with mastication and chemical stimulation (especially by
acidic tastes) of the taste buds increases the flow rate of saliva which increases washing
action to remove fermentable food and acid food/drink quickly

Front 42

what other features exist to enhance salivary buffering

Back 42

In addtion:
pH increases with flow rate
Bicarbonate concentration increases with flow rate (carbonic acid stays constant)

Front 43

why is salivary buffering described as adaptive

Back 43

Salivary buffering is adaptive
buffering capacity increases in response to
potential increases in plaque acid concentration

Front 44

without saliva what happens to the ph of the mouth

Back 44

Without saliva the pH falls below the critical pH for enamel dissolution to occur.