2. Weak acids and bases Flashcards
what does water ionize into
H+ and OH-
do free protons exist in solution? explain
no, any free proton upon water dissociation is hydrated to from H3O+, but we will usually see it as just H+
what is Keq
a fixed and dimensionless constant for a given chemical reaction. The starting concentrations do not matter
what is the Keq formula
Keq= [products] at equilibrium/[reactants] at equilibrium
in regards to amount of water ionization, what does a high Keq mean?
high Keq=high amount of water ionization
what is the formula for Kw
Kw= Keq x [H2O]
what is Kw
the ion product of water
what type of solution do we have when [H+] is high
acidic
what type of solution do we have when [H+] is low
alkaline (basic)
what is the formula for pH
pH= -log[H+]
what is the relationship between pH and [H+]
high pH=low [H+]
what does one unit jump of pH represent in regards to number of H ions
one jump represents a 10x difference
T or F: strong acids and strong bases ionize completely in water
true
describe a conjugate acid-base pair
when a weak acid loses its proton, it becomes the corresponding base pair (or proton acceptor), and together they make the conj. acid-base pair
which donates a proton: acid or base?
acid
which accepts a proton: acid or base
base
what is Ka
the acid dissociation constant. It is an equilibrium constant for ionization reactions of acids
what is the formula for pKa
pKa= -log(Ka)
what does pKa measure
the strength of the acid (the tendency it has to dissociate into a proton and its conj. base)
what does it mean when you have a low pKa
low pKa=high Ka= high level of ionization
T or F: the weaker the acid the weaker the conjugate base
false. The weaker the acid the stronger the conj. base
__ acids have a pKa less than one
strong acids
__ acids have a pKa greater than one
weak acids
what is a titration curve?
a curve showing the pH of an acidic solution when a strong base has been added
how is pH measured on a titration curve
in increments
what can a titration curve tell us about the given acid?
pKa
how can we determine the pKa of an acid using a titration curve
at the midpoint, pH=pKa
what happens as the base is added to the acid in a titration?
new OH combines with the free H+ in the solution = H2O (the free H+ was due to acid ionization)
next, the acid further ionizes to produce the H+ that was lost (shifts right), and slowly [HA] will fall and [A-] will rise as equilibrium is reached
T or F: shapes of titration curves are consistant
true, because all weak acids have the relationship: pH=pKa at the midpoint
what does the midpoint of a titration curve represent
the midpoint is where the system is 50% titrated
will a strong acid’s titration curve start lower or higher on the x axis (pH axis)
it will start lower, since strong acids have lower pH
how many inflection points will a triprotic acid have?
3
how do you deal with the 3 midpoints for a triprotic acid on a titration curve?
each midpoint represents the point where pH=pKa for that weak acid compound. (As protons are lost, each acid will have a different pKa)
how do cells keep their pH values relatively stable
they use buffer systems
what does the curve look like in the buffering region
it’s flat
how does a buffer system work
the conj acid HA has a reserve of bound protons that can be released to neutralize an addition of OH- into the system, which allows the solution to resist pH changes when small amounts of OH- or H+ are added
what is the range of a buffer system
+/- 1 pH value away from the pKa
what does the Henderson-Hasselbalch equation help us do
it allows us to connect pH, pKa, [A-], and [HA] together and descrive the shape of a weak acid titration curve
what is the Henderson-Hasselbalch equation
pH= pKa + log([A-]/[HA])
in regards to buffers, what biological importance does histidine have?
His has an amine group with pKa=6, so proteins with His residues can serve as buffers
describe the bicarbonate buffer system and how it’s useful
we have carbonic acid (H2CO3) in blood plasma which can dissociate into bicarbonate (HCO3-), and there is CO2 in the air space of the lungs. Blood often accepts excess H+ produced during exercise, so we shift toward carbonic acid. CO2 levels in blood rise, transfer to lungs, and extra is exhaled. Blood can also lose H+ from protein breakdown in the body. We shift toward bicarbonate, so CO2 from lungs dissolves into blood plasma
how is respiration rate altered (hint: think brain stem)
the brain stem is able to detect increases in blood pH or CO2 to alter respiration rate. Too much H= in blood=breathing faster and deeper to expel CO2 and adjust the equilibrium
in regards to enzyme function, why is maintaining your body’s pH important
many enzymes have a maximal activity at pH 7.4, so changes in pH can decrease enzyme activity and greatly slow essential metabolic reactions in the body
how are stored fats impacted when someone has uncontrolled diabetes (high blood sugars)
the stored fats are broken down into large amounts of ketone bodies
T or F: two of the ketone bodies that are formed during diabetes are weak acids
true
what is the issue of the two ketone bodies (produced due to diabetes) being weak acids
the acids can dissociate into their conjugate bases, which lowers blood pH and causes acidosis
describe symptoms of acidosis
drowsiness, nausea, vomiting, stupor, convulsions, and coma
what are 4 other causes of acidosis other than diabetes
starvation (cells=lacking in glucose=fat stores broken down to ketone bodies)
very heavy exercise (high buildup of lactic acid in the blood)
kidney problems (unable to regulate bicarbonate levels in the blood)
lung problems (unable to expel enough CO2)
