2. Weak acids and bases

Question 1

what does water ionize into

Answer 1

H+ and OH-

Question 2

do free protons exist in solution? explain

Answer 2

no, any free proton upon water dissociation is hydrated to from H3O+, but we will usually see it as just H+

Question 3

what is Keq

Answer 3

a fixed and dimensionless constant for a given chemical reaction. The starting concentrations do not matter

Question 4

what is the Keq formula

Answer 4

Keq= [products] at equilibrium/[reactants] at equilibrium

Question 5

in regards to amount of water ionization, what does a high Keq mean?

Answer 5

high Keq=high amount of water ionization

Question 6

what is the formula for Kw

Answer 6

Kw= Keq x [H2O]

Question 7

what is Kw

Answer 7

the ion product of water

Question 8

what type of solution do we have when [H+] is high

Answer 8

acidic

Question 9

what type of solution do we have when [H+] is low

Answer 9

alkaline (basic)

Question 10

what is the formula for pH

Answer 10

pH= -log[H+]

Question 11

what is the relationship between pH and [H+]

Answer 11

high pH=low [H+]

Question 12

what does one unit jump of pH represent in regards to number of H ions

Answer 12

one jump represents a 10x difference

Question 13

T or F: strong acids and strong bases ionize completely in water

Answer 13

true

Question 14

describe a conjugate acid-base pair

Answer 14

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

Question 15

which donates a proton: acid or base?

Answer 15

acid

Question 16

which accepts a proton: acid or base

Answer 16

base

Question 17

what is Ka

Answer 17

the acid dissociation constant. It is an equilibrium constant for ionization reactions of acids

Question 18

what is the formula for pKa

Answer 18

pKa= -log(Ka)

Question 19

what does pKa measure

Answer 19

the strength of the acid (the tendency it has to dissociate into a proton and its conj. base)

Question 20

what does it mean when you have a low pKa

Answer 20

low pKa=high Ka= high level of ionization

Question 21

T or F: the weaker the acid the weaker the conjugate base

Answer 21

false. The weaker the acid the stronger the conj. base

Question 22

__ acids have a pKa less than one

Answer 22

strong acids

Question 23

__ acids have a pKa greater than one

Answer 23

weak acids

Question 24

what is a titration curve?

Answer 24

a curve showing the pH of an acidic solution when a strong base has been added

Question 25

how is pH measured on a titration curve

Answer 25

in increments

Question 26

what can a titration curve tell us about the given acid?

Answer 26

pKa

Question 27

how can we determine the pKa of an acid using a titration curve

Answer 27

at the midpoint, pH=pKa

Question 28

what happens as the base is added to the acid in a titration?

Answer 28

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

Question 29

T or F: shapes of titration curves are consistant

Answer 29

true, because all weak acids have the relationship: pH=pKa at the midpoint

Question 30

what does the midpoint of a titration curve represent

Answer 30

the midpoint is where the system is 50% titrated

Question 31

will a strong acid's titration curve start lower or higher on the x axis (pH axis)

Answer 31

it will start lower, since strong acids have lower pH

Question 32

how many inflection points will a triprotic acid have?

Answer 32

3

Question 33

how do you deal with the 3 midpoints for a triprotic acid on a titration curve?

Answer 33

each midpoint represents the point where pH=pKa for that weak acid compound. (As protons are lost, each acid will have a different pKa)

Question 34

how do cells keep their pH values relatively stable

Answer 34

they use buffer systems

Question 35

what does the curve look like in the buffering region

Answer 35

it's flat

Question 36

how does a buffer system work

Answer 36

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

Question 37

what is the range of a buffer system

Answer 37

+/- 1 pH value away from the pKa

Question 38

what does the Henderson-Hasselbalch equation help us do

Answer 38

it allows us to connect pH, pKa, [A-], and [HA] together and descrive the shape of a weak acid titration curve

Question 39

what is the Henderson-Hasselbalch equation

Answer 39

pH= pKa + log([A-]/[HA])

Question 40

in regards to buffers, what biological importance does histidine have?

Answer 40

His has an amine group with pKa=6, so proteins with His residues can serve as buffers

Question 41

describe the bicarbonate buffer system and how it's useful

Answer 41

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

Question 42

how is respiration rate altered (hint: think brain stem)

Answer 42

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

Question 43

in regards to enzyme function, why is maintaining your body's pH important

Answer 43

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

Question 44

how are stored fats impacted when someone has uncontrolled diabetes (high blood sugars)

Answer 44

the stored fats are broken down into large amounts of ketone bodies

Question 45

T or F: two of the ketone bodies that are formed during diabetes are weak acids

Answer 45

true

Question 46

what is the issue of the two ketone bodies (produced due to diabetes) being weak acids

Answer 46

the acids can dissociate into their conjugate bases, which lowers blood pH and causes acidosis

Question 47

describe symptoms of acidosis

Answer 47

drowsiness, nausea, vomiting, stupor, convulsions, and coma

Question 48

what are 4 other causes of acidosis other than diabetes

Answer 48

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)