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stuff ni jas > pH and buffers > Flashcards

pH and buffers Flashcards

1
Q

how does a pH meter measure the acidity or alkalinity of a substance?

A

by weighing the hydrogen-ion movement in water-based suspensions

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2
Q

pH is also called? and why is it called that?

A

potentiometric pH meter because it measures the electrical potential variation between pH electrode and reference electrode

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3
Q

where is the word pH derived from?

A

“p” is the scientific figure for negative logarithm
“H” is for hydrogen

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4
Q

range of pH?

A

0-14

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5
Q

equation to get pH?

A

pH = -log[H+]

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6
Q

who introduced the glass electrode idea?

A

Fritz Haber and his student Zygmunt Klemensiewicz

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7
Q

who introduced the pH meter? and when

A

1934 by Arnold Beckam

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8
Q

if the hydrogen density/concentration is greater than the hydroxide density/concentration the solution is?

A

acidic
pH < 7

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9
Q

if the hydrogen density/concentration is less than the hydroxide density/concentration the solution is?

A

basic
pH > 7

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10
Q

neutral pH?

A

7

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11
Q

how many electrodes does a pH have?

A

2 (measuring and reference electrode)

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12
Q

what is the reference electrode?

A

has a neutral solution such as KCl with a fixed concentration and gives a stable voltage

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13
Q

what is the measuring electrode?

A

it depends totally upon the pH of the suspension

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14
Q

what is the algebraic total of the potentials of the measuring and reference electrode, and liquid junction called?

A

overall potential or voltage

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15
Q

what happens when both electrodes are immersed in the suspension?

A

ion-exchange happens wherein hydrogen ions flow towards the outer surface of the measuring electrode and displace some metal ions inside

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16
Q

true or false: some of the variation is pH is not negligible therefore produces an unstable voltage

A

false

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17
Q

where does ion-exchange take place?

A

inside the surface of the glass electrode to generate a potential variation

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18
Q

what requires calibration to prepare for precise pH measurement?

A

the voltage studies in the impedance voltmeter

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19
Q

wash the electrodes with what?

A

distilled water

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20
Q

maintain the sample’s temperature at how much?

A

25C

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21
Q

true or false: immerse the electrodes and stir the solution to create a homogenous mixture

A

true

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22
Q

what are the pH meters based on portability?

A

portable pH meter: compact DC power equipment
desktop pH meter: same as portable
pen pH meter: single scale, conventional measurement range, easy and handy

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23
Q

pH meters based on purpose?

A

laboratory pH meter: multi-function, high accuracy
industrial online pH meter: excellent stability, steady work, specific level of measurement efficiency, environmental flexibility

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24
Q

pH meters based on advanced level?

A

economic pH meter
intelligent pH meter
precision pH meter/ digital pH meter

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25
Q

what are the 3 types of electrodes?

A

glass
reference
combination gel

26
Q

what are the applications of pH meter?

A

agricultural industries
measure water quality
chemical and pharmaceutical industries
food industry (dairy products)
detergents

27
Q

advantages of pH meter?

A

calibration is low prices and robust
user friendly
reliable and specific

28
Q

disadvantages of pH meter?

A

heat affects readings
pH calibration using glass electrodes need to be clean since dirt influences the readings

29
Q

true or false: most biochemical reactions occur in an aqueous environment

A

true

30
Q

why is water highly polar?

A

bc of its bent geometry

31
Q

why is water highly cohesive?

A

bc of hydrogen bonding

32
Q

how to get pOH?

A

pOH = -log[OH-]

33
Q

is an acid a proton acceptor or donor?

A

donor

34
Q

is the base a proton acceptor or donor?

A

acceptor

35
Q

true or false: [AH] is the conjugate base and [A] is the acid

A

false, [AH] is the acid and [A] is the conjugate base

36
Q

true or false: [BH] is the base and [B] is the conjugate acid

A

false, [BH] is the conjugate acid and [B] is the base

37
Q

acidic or basic: [H+] > 10^-7

A

acidic

38
Q

acidic or basic: [OH-] > 10^-7

A

basic

39
Q

what is the physiological pH?

A

6.5-8.0

40
Q

how does less pKa affect the pH?

A

less pKa = more Ka = more acidic

41
Q

true or false: polyprotic acids can lose more than one proton

A

true

42
Q

true or false: each dissociation of polyprotic acids have one Ka and pKa value for all

A

false, each dissociation has its own unique Ka and pKa

43
Q

what is the biological definition of a buffer?

A

solution that resists change in pH when adding an acid or base

44
Q

what is the chemical definition of a buffer?

A

mixture of a weak acid and its conjugate base with a buffering range of pKa+ or - 1

45
Q

buffer pair (WA + CB) when adding strong base will yield what?

A

CB and H2O

46
Q

buffer pair (WA + CB) when adding strong acid will yield what?

A

more weak acid

47
Q

what are ampholytes?

A

ionizing groups that have acidic and basic pKa

48
Q

the ionic form of each compound is dependent on what?

A

the pH of the solution

49
Q

if the pH of the solution is greater than the pKa, what form does it take?

A

conjugate base form deprotonated

50
Q

if the pH of the solution is less than the pKa, what form does it take?

A

conjugate acid form protonated

51
Q

what is the chemical formula for glycine?

A

H2N - CH2 - COOH

52
Q

what is the pKa of the carboxylate and amino groups in glycine?

A

carboxylate : 2.3
amino : 9.6

53
Q

what is a zwitterion?

A

ionic form of a substance that has a net charge of 0

54
Q

what is the isoelectric point (pI)?

A

pH at which the net charge on the ampholyte is 0

55
Q

true or false: pH and pI are equal

A

true

56
Q

what is an acidic buffer composed of?

A

weak acid + salt of a strong base

57
Q

what is a basic buffer composed of?

A

weak base + salt of a strong acid

58
Q

when the condensation of the conjugate acid is equal to the conjugate base what happens?

A

pH = pKa or pOH = pKb

59
Q

what is buffer capacity?

A

number of H ions that can be added to 1L of solution to decrease the pH by 1 unit or the number of OH ions that can be added to 1L solution to increase the pH by 1 unit

60
Q

what is the unit of buffer capacity?

A

moles

stuff ni jas (20 decks)

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