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Flashcards in pH and Buffers Deck (31)
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1

Definition of pH

Measure of H+ conc that are free in a solutionq

2

Definition of buffers

Weak acid + conjugate base
can resist abrupt and large pH changes in the body fluids by releasing H+ when pH in creases, binding H+ when pH decreases

3

Definition of a strong acid

H+ completely dissociates in solution

4

Definition of a strong base

OH- completely dissociates in solution

5

Definition of a weak acid

H+ partially dissociates in solution

6

Definition of a weak base

OH- partially dissociates in solution

7

Definition of ionization of water

Process by which water splits into their H+ and OH- in solution

8

Definition of Ka

Acid dissociation constant, greater the constant, the stronger the acid, smaller the constant, the weaker the acid

9

Definition of pKa

pH at which the acid is half dissociated, same amount of undissociated acid and conjugate base.

10

Why is blood pH maintained

In contact with nearly every body cell
Acidosis/alkalosis can occur is not maintained

11

Living range and regulated pH levels

7.0-7.8
7.35-7.45

12

Where does acids in the body come from

By food
Protein breakdown
incomplete oxidation of fats/glucose
Loading/transport of CO2 in blood

13

How is the acid base balance regulated

Lungs (ventilation)
Kidney (monitor and adjust blood pH)
Chemical buffers

14

Buffer operation

When pH too high, H+ released
When pH too low, H+ binds

15

Range of buffer operation

1-2

16

Water content of humans

Infants=73%
Healthy male=60%
Healthy female=50%
Old age=45%

17

Conc of pure water

55.6M

18

Keq equation

[H+]/[H2O] = Keq
[1.0 x 10-7]/[55.6] = 1.8 x 10-14

19

Kw equation

[H+][OH-] = Kw = 1.0 x 10-7

20

How to calculate pH and [H+]

-log[H+] = pH
10-pH = [H+]

21

Analyzing titration curves

Mid point of horizontal section = pKa
pKa = pH at which the buffer is strongest
Midpoint = midpoint between total and 0 dissociation

22

How to calculate pKa and Ka

pKa = -log(Ka)

23

Henderson-Hasselbalch equation

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

24

Physiologically important buffers

Saliva
H2CO3 => HCO3-
H2PO4- => HPO4 2-
Protein + => protein

25

Amino acids and buffers on titration

NH3+ and COO- has pKa values
No buffering at zwitterion

26

Amino acids involved in buffering

Histidine (pKa at 6) and cysteine

27

How can haemoglobin be a buffer

Hb has many histidine residues, within physiological pH

28

Change of pKa of a group

Histidine pKa in Hb has different pKa to free His
Neighboring groups affect pKa

29

How does oxyhemoglobin and deoxyhaemoglobin affects buffers

Deoxy, greater pKa than Oxy, better buffer
Greater difference between deoxy pKa and blood pH when carbonic acid conc is high, absorbs H+ as weaker acid than oxy

30

Lipid soluble molecules and diffusion at different pH

When lipids are charged, cannot pass through membrane at certain pHs