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Biochemistry: Cellular Composition > Week 1 practical - pH and buffers > Flashcards

Week 1 practical - pH and buffers Flashcards

(78 cards)

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1
Q

acidity

A

measure of H+ concentration

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2
Q

pH definition

A

pH = -log10[H+]

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3
Q

[H+]

A

[H+] = 10^-pH

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4
Q

[H+] of pure water

A

1.0x10^-7

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5
Q

why do we use pH to measure acidity as opposed to H+ concentration?

A

H+ is small and varies widely

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6
Q

acids

A

proton donators

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7
Q

bases

A

proton acceptors

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8
Q

what type of acids are carboxylic acids?

A

weak

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9
Q

what do pipettes give their maximum volume in?

A

micro litres

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10
Q

what do we use to set the volume on a pipette?

A

thumbwheel

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11
Q

how do we know which tip to use on a pipette?

A

match the tip colour with the colour of the push button

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12
Q

what would we set the pipette to to measure 2 micro litres?

A

P20

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13
Q

how many microlitres in 1ml?

A

1000

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14
Q

what is a P20 pipette used to measure?

A

2-20 microlitres

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15
Q

what is a P200 pipette used to measure?

A

20-200 microlitres

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16
Q

what is a P1000 pipette used to measure?

A

between 200-1000 microlitres

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17
Q

what is a P5000 pipette used to measure?

A

1000-5000 microlitres

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18
Q

on which pipette do we need to twist the tip to tighten?

A

P5000

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19
Q

extra step when using P5000 pipette

A

twist tip to tighten

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20
Q

what must we do when not using the glass electrode bulb?

A

keep it moist

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21
Q

how many microlitres in 1ml?

A

1000

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22
Q

steps to calibrating a pH meter

A

-place electrode in the pH 7 standard buffer first
-completely immerse glass electrode bulb for an accurate reading
-agitate probe for faster reading
-reading to within 0.02 units of the pH 7 using “buffer offset”
-rinse then place electrode in the pH 4 standard buffer - adjust reading to within 0.02 units of the pH of the chose buffer using “slope %”
-probe back in pH 7 and shake gently
= meter is calibrated
=reading within 0.05 pH units of 7 (repeat if not)
+ remember to replace the calibrated electrode in the storage solution (bulb dries out = damaged)

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23
Q

steps to taking a measurement with a pH meter

A

-rinse and blot electrode before using (to avid contamination of measured solution)
-completely immerse glass electrode bulb and shake
-stabilise to 0.02 units before recording

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24
Q

what do pipettes give their maximum volume in?

A

micro litres

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25
how many pH units should a reading be within once it's been calibrated?
0.05
26
on which pipette do we need to twist the tip to tighten?
P5000
27
what do we do before using the electrode on a pH meter and why?
rinse with distilled water to avoid contamination
28
what do we use to set the volume on a pipette?
thumbwheel
29
what must we do when not using the glass electrode bulb?
keep it moist
30
what type of acids are carboxylic acids?
weak
31
what would we set the pipette to to measure 2 microlitres?
P20
32
Ka equation + define symbols
Ka = [A-][H+]/[HA] HA = weak acid A- = conjugate base H+ = proton
33
what's the difference between a conjugate acid and conjugate base?
the presence of an additional proton
34
what is the only thing the Henderson-Hasselbalch equation can be used for?
for conjugate acid-base pairs
35
pKa equation
pKa = -logKa
36
can the henderson-hasselbalch equation be used for acids and bases that react together?
no, only for conjugate acid-base pairs
37
conjugate acid and base pair equation
acid --><-- base + H+
38
Henderson-Hasselbalch equation
pH = pKa + log10 [A-]/[HA]
39
derivation of Henderson-Hasselbalch equation
Ka = [A-][H+]/[HA] take logs of both sides log Ka = log [A-][H+]/[HA] rearrange log Ka = log [A-]/[HA] + log [H+] rearrange -log[H+] = -logKa + log [A-]/[HA] definitions of pH and pKa pH = pKa + log [A-]/[HA]
40
Uses of Henderson-Hasselbalch equation
- describe how concentrations of conjugate acid and base in a buffer solution change at different solutions - find pKa of a buffer (mix known amounts of conjugate acid + base + see how concentration changes) -pH = pKa --> concentrations of conjugate acid + base are equal -predict how a solution will respond to adding a strong acid or base
41
how do we know if the concentrations of conjugate acid and base are equal?
pH = pKa
42
what does it mean if pH = pKa?
the concentrations of conjugate acid and base are equal
43
what are biochemical reactions sensitive to?
pH
44
why is the pH of the body tightly regulated?
biochemical reactions are sensitive to pH
45
acidosis
when the pH of the blood plasma is less than 7.35
46
when the pH of the blood plasma is less than 7.35
acidosis
47
symptoms of acidosis
headaches, confusion, breathlessness, coma
48
what are there to control intracellular pH?
proteins that pump protons out of cells buffers
49
major buffer in blood and interstitial fluid
bicarbonate buffer system
50
where is the bicarbonate buffer system found?
it's a major buffer in blood and interstitial fluid
51
bicarbonate buffer system equation
CO2 + H2O --><-- H2CO3 --><-- HCO3- + H+
52
why is there CO2 in the bicarbonate buffer system equation?
produced in the tissues
53
carbonic acid
H2CO3
54
what happens to the carbonic acid in the bicarbonate buffer system?
it ionises immediately
55
bicarbonate ions
HCO3-
56
how do clinicians estimate the concentration of HCO3- in patient's plasma?
from... pH [CO2] HH equation use a pKa of 6.1
57
name a buffer commonly used in biochemistry
phosphate
58
why is phosphate a buffer that's commonly used in biochemistry?
3 ionisable groups = 3 pKas and 4 different chemical forms
59
ionisation
gain or lose electrons
60
how much of the ionic species is remaining at 2 pH units from the pKa and why?
1/100 pH is a log function
61
what happens to the phosphate buffer at different pHs?
different concentrations of the different forms of phosphate in the buffer
62
forms of phosphate in the buffer
H3PO4 H2PO4- HPO4^2- PO4^3-
63
at which pH is phosphate in the H3PO4 form in the buffer?
low pH
64
at which pH is phosphate in the PO4^3- form in the buffer?
high pH
65
what do we have when pH = pKa?
equal concentrations of conjugate acid and base (careful with H2)
66
what is true when we have equal concentrations of conjugate acid and base?
pH = pKa (careful with H2)
67
when is a buffer most resistant?
when [conjugate acid] = [conjugate base]
68
describe the buffer when [conjugate acid] = [conjugate base]
most resistant
69
what does a greater difference between the pH and the pKa lead to?
a greater difference between the relative concentrations of acid and conjugate base
70
when do buffers function best?
within one pH unit of their pKa
71
why do buffers function best within one pH unit of their pKa?
because pKa is the -log of Ka
72
when do we have a greater difference between the relative concentrations of acid and conjugate base?
when there's a greater difference between the pH and the pKa
73
which buffer should we choose and why?
one with a similar pKa to the pH of the solution you want to use buffers function best within one pH unit of their pKa
74
what gives a buffer a greater buffering capacity?
greater concentration of the buffer
75
buffer concentration often used by biochemists
10-100mmol.L-1
76
why are buffers used a lot?
near-physiological pKa lack of toxicity tend not to interfere with biochemical reactions
77
examples of buffers used + pKa
MES 6.1 phosphate 6.9 HEPES 7.5 Tris 8.1
78
What would we set the pipette to to measure 450 micro litres? Explain
P45 On P1000, bottom number is 10 micro litres

Biochemistry: Cellular Composition (1 decks)

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