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CELLULAR BASIS OF MEDICINE > PHOSPHATE BUFFER PRACTICAL > Flashcards

PHOSPHATE BUFFER PRACTICAL Flashcards

1
Q

WHAT IS A BUFFER?

A

solution that prevents a drastic pH chage
-consists of a conjugate pair -> acid and conjugate base or base and conjugate acid
-weak acid - salt = negative ion (conjugate base)
-weak base - salt = positive (conjugate acid)
-2 different salts of the same polyprotic acid
-an amphoteric electrolyte (protein)

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2
Q

WHAT ARE THE MOST IMPORATANT BUFFERS IN THE HUMAN BODY?

A

-carbonate, phosphate, hemoglobin

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3
Q

WHAT ARE BUFFERS USED FOR IN THE LAB?

A

buffers are used to prepare solutions of known stable pH - they are used as standard solutions to calibrate pH meter or help maintain pH of some reaction mixtures

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4
Q

WHAT DO PROTONS REACT WITH?

A

conjugate base

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5
Q

WHAT DO HYDROXIDE IONS REACT WITH?

A

conjugate acid

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6
Q

WHAT HAPPENS WHEN AN ACID IS ADDED TO THE SOLUTION?

A

most of the extra protons are removed / neutralized by the base

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7
Q

WHAT HAPPENS WHEN A BASE IS ADDED TO THE SOLUTION?

A

most of the extra hydroxide ions are removed by a reaction with undissociated acid

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8
Q

WHAT IS THE BEST RATIO FOR A BUFFER?

A

ratio 1:1 of the conjugate pair is the most efficient for handling the addition of either a base or an acid

-> If the buffer contains much
more conjugate acid than conjugate base, it is less efficient in handling in acid. Alternatively, a buffer with much more of the conjugate base than of conjugate acid cannot efficiently counteract the addition of a base.
For example, the H2CO3 / HCO3
- buffer in blood has a 1:20 ratio of acid to its conjugate base. Blood is then more effective in counteracting acids, which are the products of metabolism

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9
Q

ACIDIC BUFFER CALCULATION

A

pH = pKa + log (csalt/cacid)

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10
Q

BASE BUFFER CALCULATION

A

pOH = pKb + log (csalt/ cbase)
pH = 14 - pOH

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11
Q

WHAT IS pKa?

A

negative common logarithm of the dissociation constant of the acid (pKa = - log Ka)

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12
Q

WHAT IS Ka?

A

an equilibrium constant describing a dissociation of the acid: HA <–> H+ + A-
(i.e. Ka is andissociation constant of the acid)

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13
Q

WHAT IS pKb

A

negative common logarithm of the dissociation constant of the hydroxide (pKb = - log Kb)

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14
Q

WHAT IS Kb?

A

an equilibrium constant describing a dissociation of the hydroxide: BOH  B+ + OH-
(i.e. Kb is an dissociation constant of the hydroxide)

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15
Q

WHAT IS THE MOST EFFICIENT BUFFER?

A

pH = pK (the ratio of concentrations is 1/1 because log(1/1) = 0), sufficient efficiency is found if a buffer pH = pK ± 1 (it is related to the ratio of 1/10 or 10/1)

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16
Q

ACIDIC BUFFER WITH MOLAR CONCENTRATION

A

pH = pKa + log (c´salt x Vsalt / c´acid x Vacid)

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17
Q

BASIC BUFFER WITH MOLAR CONCENTRATION

A

pOH = pKb + log (c´salt x Vsalt / c´base x Vbase)
pH = 14 - pOH

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18
Q

WHAT IS THE CAPACITY OF A BUFFER?

A

the substance amount of acid or base it must be added into the buffer to change its pH by 1 pH unit (substance amount of acid or base divided by related pH change).
-buffer has its highest capacity at equal concentrations of weak acid and conjugate base, when p H = p K a
-to increase capacity -> increase total concentration

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19
Q
A
20
Q

DEFINE POTENTIOMETRY

A

electrochemical analytical method that is based on the measurement of voltage of an electrochemical cell when no current flows

21
Q

WHAT IS A WORKING / INDICATING ELECTRODE?

A

sensitive for a compound of interest – its potential is changed if an activity (concentration) of the compound is changed

22
Q

WHAT IS A REFERENCE ELECTRODE?

A

one whose potential is stable
- The electrode potential of those electrodes is constant, it is not influenced by
ion of interest.

EG: metal wire covered by layer of an insoluble salt that has common cation with the wire; it is
dipped into a solution that has the same anion with the insoluble salt (e.g. argentchloride electrode:
Ag/AgCl/solution of saturated KCl; calomel electrode: Hg/Hg2Cl2/solution of saturated KCl)

23
Q

WHAT IS THE ELECTRODE POTENTIAL?

A

“expression of energy” of processes proceeding on the electrode. It is defined as the voltage of the electrochemical cell that consists of this electrode as a cathode and a standard hydrogen electrode (SHE) as an anode

24
Q

WHAT IS THE ELECTRON POTENTIAL OF THE SHE ELECTRODE?

A

0.00 volts under all temperatures

25
Q

WHAT DOES THE NERNST PETERSON EQUATION REPRESENT?

A

relationship between the electrode potential and the activity of any ion of interest

26
Q

WHAT DOES POTENTIOMETRIC ANALYSIS CONTAIN?

A

-voltmeter
-reference electrode
-salt bridge
-analyte
-indicator electrode
-magnetic mixer

27
Q

NERNST PETERSON EQUATION

A

IF REDOX PAIR IN STANDARD THE STATE THE EQUATION IS SIMPLIFIED

28
Q

DEFINE ANODE

A

the electrode at which oxidation occurs; anions move toward the anode because it is
positively charged

29
Q

DEFINE ANODE

A

the electrode at which oxidation occurs; anions move toward the anode because it is
positively charged

30
Q

DEFINE CATHODE

A

the electrode at which reduction occurs; cations move toward the cathode because it is
negatively charged

31
Q

DEFINE CURRENT

A

the flow of charge
-> current of 1 ampere = 1 coulomb per sec

32
Q

DEFINE POTENTIAL

A

it is an expression of energy; the gradient (slope) of a potential causes charge to move;
the movement of one coulomb of charge from a potential of V to a potential of V-1 volts requires one joule of energy

33
Q

WHAT IS A SALT BRIDGE?

A

a device that allows charge to flow as ions between two separate containers of
electrolyte that are also connected by metallic conductors

34
Q

WHAT IS FARADAYS CONSTANT?

A

the number of coulombs in a mole of electrons which is 96 485 coulombs per mole

35
Q

WHAT IS POTENTIOMETRY USED FOR IN VOLUMETRIC ANALYSIS?

A

for indication of a point of equivalence during neutralization or redox reactions

36
Q

WHAT ARE MEMBRANE / ION SELECTIVE ELECTRODES?

A

potentiometric electrodes that develop a potential in the presence of one ion (or class of ions) but not in the presence of a similar concentration of other ions

EG: electrodes specific to H+, Na+, K+, Cl-

37
Q

WHAT IS THE GLASS ELECTRODE?

A

glass membrane sensitive to H+ and it is commonly used for determination of solution pH

38
Q

WHICH ELECTRODE IS DIFFERENT TO OTHER TYPES BASED OF THE PRINCIPLE OF ELECTRODES?

A

ion selective electrodes

39
Q

WHAT IS A COMBINATION ELECTRODE?

A

glass electrode and reference electrode

40
Q

IONIC PRODUCT OF WATER

A
41
Q

EQUILIBRIUM CONSTANT OF WATER

A
42
Q

DEFINE EQUILIBRIUM CONSTANT

A

a value that links the amounts of reactants and products in a reversible reaction at equilibrium

43
Q

WEAK ACIDS AND BASES

A
44
Q

DISSOCIATION OF TRIHYDROGEN PHOSPHORIC ACID

A
45
Q

EXAMPLES OF REFERENCE ELECTRODES

A

argentchloride
calomel

  • metal wire and layer of insoluble salt in common with the cation of the wire
46
Q

WHAT IS USED TO CALIBRATE THE PH MACHINE?

A

Two buffers of known solution are used to set relationship between known value of ph and a measured value of ph

CELLULAR BASIS OF MEDICINE (32 decks)

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