Acids, Bases and Buffers Flashcards
what are buffers important in
living systems
what do buffers do
they maintain the pH of the body within normal pH ranges
they ensure enzymes and other cellular processes function optimally
what are examples of inorganic buffers
phosphate and bicarbonate
what is the normal pH for blood
7.4
what is the normal pH range for urine
6
what is the normal pH for gastric fluid
2
what is the normal pH for saliva
6.2-7.2
what is an example of a macromolecule in the body that can act as a buffer
amino acids
are many molecules in biological systems weak acids/bases or strong acids/bases
weak
what can ionic properties be influenced by
hydrogen ion concentration
what are bases
substances that usually combine with hydrogen ions in water
the greater the acid dissociation constant…
…the stronger the acid
what is the henderson-hasselbalch equation
pH = pka + log10 [B-]/[A]
how can you determine pH
using indicators or electrical methods like a pH meter
how can indicators be used to determine pH
they show a difference of colour between their ionised and deionised form. ratio of ionised to deionised indicator is determined by pH and this ratio determines the colour of the indicator. the depth of colour of the indicator can be used to measure pH
what is the ionised form of indicators
[In-]
what is the deionised form of indicators
[HIn]
what are indicators
weak acids that show a difference of colour when ionised which is used to determine the pH of a solution
how much indicator is used
not a lot - the pH cant be altered by it this way
why is only a small amount of indicator ever used
so the pH is not altered
equationto show how the degree of dissociation and pH is related
pH = pKa + log10 [In-] / [HIn]
what is the most accurate way of determining pH
pH meter
are electric methods more effective at determining pH than indicators
yes
how can the pH measurement be made by pH meters
using a glass electrode.
what are glass electrodes
thin walled glass bulbs containing a platinum electrode immersed in 1M of hydrochloric acid
what are buffer solutions
solutions that resist changes in pH when acid or base is added
what do buffer solutions consist of
a conjugate acid-base pair of either a weak acid or a weak base
what role do buffers play in the body
maintaining pH homeostasis
what does buffering in the mouth limit
pH changes due to the acid produced by plaque bacteria
how may the pH in the mouth change
the acid produced by the plaque bacteria
when do buffers operate optimally
when they are 50% dissociated
when is buffering most effective
when the concentration of the acid and the base are equal
how do plaque bacteria produce acid
by fermenting dietary carbohydrate
how does the plaque pH fall
production of acid from the fermentation of carbohydrates from the diet
how is dental caries formed by plaque bacteria
- the bacteria ferment dietary carbohydrate to produce acid
- this acid reduces the pH
- this leads to increased solubility of dental enamel
- this results in dental caries if not reversed
how is the acid produced by plaque bacteria neutralised
the saliva acts as a buffer
can the buffering of saliva to neutralise acid produced by plaque bacteria prevent dental caries
if the buffering is adequate
what does saliva contain that aids buffering
proteins which are histidine rich known as histatins
what is an important buffer in the body that can be found in such things as blood
bicarbonate
what is another useful buffer that is not important physiologically
sodium acetate
why is sodium acetate useful in biochemistry
illustrates the principle of buffering
what is buffering capacity
this is the volume that can be added before there is a dramatic change in pH
what form does histidine exist in when at a neutral pH
zwitterion form
what does it mean if an amino acid is in its zwitterion form
both a positive and a negative charge is being carried
