pH and H2O

Question 1

Dissociation of H2O

Answer 1

H2O H+ + OH-
Keq=[H+] [OH-] / [H2O] = 1.8 X 10^-16
[H2O] = 55.6g/mol
[H+] = 1 X 10^-7
[OH-] = 1X 10^-7

Question 2

strong acid dissociation

Answer 2

complete

HA –> A- + H3O+ (in H2O)
acid transfers proton to H2O making hydronium ion

final [H3O+] = initial [HA]
virtually no HA left in solution

Ka very large and pKa small
Ka= [H3O+] [A-] / [HA]&raquo_space;1
contribution of H+ from H2O not needed to be considered

Question 3

dissociation of weak acids

Answer 3

[H+] contributed by H2O is significant

Ka is small, and pKa is very large…because of little proton dissociation
the larger the Ka, the more dissociation

Henderson-Hasselbach equation
pH=pKa + log[A-]/[HA] or pH=pKb + log[B+]/[BOH]
pH=[H+] [A-] / [HA] or pH = [B+] [OH-] / [BOH]

Question 4

calculating [H+] or [OH-]

Answer 4

pH = -log[H+]

[H+] [OH-] = 1 X 10^-14

Question 5

Bronsted acid and base

Answer 5

acid=proton donor, base=proton acceptor

HA H+ + A-
where HA is the conjugate acid and A- is the conjugate base

Question 6

ionization constant

Answer 6

pKa = -logKa

to figure out pH use Henderson-Hasselbach

when conj acid = conj base…pH=pKa

Question 7

polyprotic acids

Answer 7

have mult H+ to lose

1st Ka tends to be larger (pKa-lower)
because 1st proton is easier to lose; losing the second makes the molecule negative so it’s harder to lose

Question 8

what factors affect buffering capabilities?

Answer 8

1) molecular [ ] of buffer components…buffer is stronger when both buffer components [ ] inc
2) pKa…buffers are usually a mix of a weak acid and its conj base

Question 9

best buffers

Answer 9

for any particular purpose the buffer who’s pKa is closest to the desired pH is the best

Question 10

what are physiological buffer systems

Answer 10

carbonate and phosphate

Question 11

phosphate buffer

Answer 11

pH control in Kidneys

H2PO4- H+ + HPO4-2

Question 12

how do the kidneys affect blood pH?

Answer 12

phosphate buffer: H2PO4- H+ + HPO4-2

reabsorption or production of HCO-3 when needed

Question 13

bicarbonate buffer

Answer 13

H+ + HCO3- H2CO3 CO2 + H2O
where CO2 + H2O H2CO3 requires carbonic anhydrase

remember CO2 conversion

Question 14

determining [CO2]

Answer 14

multiply by 0.03

pCO2 X 0.03mM/mmHg @ 37C

Question 15

hyperventilation

Answer 15

physiological response to acidic blood pH

dec CO2 in body -> inc ratio [HCO3-]/[CO2] -> dec pCO2 -> dec acidity/inc pH

Question 16

hypoventilation

Answer 16

lower [HCO3-]/[Co2] ratio -> inc pCO2 -> dec pH/inc pH

Question 17

CO2 through the body

Answer 17

http://www.ric.edu/faculty/jmontvilo/335files/335(27)respirationmech.htm

Question 18

Amphoteric

Answer 18

species that can react with either acid or base

simple dissociation of H2O generates both H+ and OH-