pH and buffers

Question 1

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

Answer 1

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

Question 2

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

Answer 2

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

Question 3

where is the word pH derived from?

Answer 3

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

Question 4

range of pH?

Answer 4

0-14

Question 5

equation to get pH?

Answer 5

pH = -log[H+]

Question 6

who introduced the glass electrode idea?

Answer 6

Fritz Haber and his student Zygmunt Klemensiewicz

Question 7

who introduced the pH meter? and when

Answer 7

1934 by Arnold Beckam

Question 8

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

Answer 8

acidic
pH < 7

Question 9

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

Answer 9

basic
pH > 7

Question 10

neutral pH?

Answer 10

7

Question 11

how many electrodes does a pH have?

Answer 11

2 (measuring and reference electrode)

Question 12

what is the reference electrode?

Answer 12

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

Question 13

what is the measuring electrode?

Answer 13

it depends totally upon the pH of the suspension

Question 14

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

Answer 14

overall potential or voltage

Question 15

what happens when both electrodes are immersed in the suspension?

Answer 15

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

Question 16

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

Answer 16

false

Question 17

where does ion-exchange take place?

Answer 17

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

Question 18

what requires calibration to prepare for precise pH measurement?

Answer 18

the voltage studies in the impedance voltmeter

Question 19

wash the electrodes with what?

Answer 19

distilled water

Question 20

maintain the sample’s temperature at how much?

Answer 20

25C

Question 21

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

Answer 21

true

Question 22

what are the pH meters based on portability?

Answer 22

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

Question 23

pH meters based on purpose?

Answer 23

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

Question 24

pH meters based on advanced level?

Answer 24

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

Question 25

what are the 3 types of electrodes?

Answer 25

glass reference combination gel

Question 26

what are the applications of pH meter?

Answer 26

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

Question 27

advantages of pH meter?

Answer 27

calibration is low prices and robust user friendly reliable and specific

Question 28

disadvantages of pH meter?

Answer 28

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

Question 29

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

Answer 29

true

Question 30

why is water highly polar?

Answer 30

bc of its bent geometry

Question 31

why is water highly cohesive?

Answer 31

bc of hydrogen bonding

Question 32

how to get pOH?

Answer 32

pOH = -log[OH-]

Question 33

is an acid a proton acceptor or donor?

Answer 33

donor

Question 34

is the base a proton acceptor or donor?

Answer 34

acceptor

Question 35

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

Answer 35

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

Question 36

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

Answer 36

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

Question 37

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

Answer 37

acidic

Question 38

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

Answer 38

basic

Question 39

what is the physiological pH?

Answer 39

6.5-8.0

Question 40

how does less pKa affect the pH?

Answer 40

less pKa = more Ka = more acidic

Question 41

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

Answer 41

true

Question 42

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

Answer 42

false, each dissociation has its own unique Ka and pKa

Question 43

what is the biological definition of a buffer?

Answer 43

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

Question 44

what is the chemical definition of a buffer?

Answer 44

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

Question 45

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

Answer 45

CB and H2O

Question 46

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

Answer 46

more weak acid

Question 47

what are ampholytes?

Answer 47

ionizing groups that have acidic and basic pKa

Question 48

the ionic form of each compound is dependent on what?

Answer 48

the pH of the solution

Question 49

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

Answer 49

conjugate base form deprotonated

Question 50

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

Answer 50

conjugate acid form protonated

Question 51

what is the chemical formula for glycine?

Answer 51

H2N - CH2 - COOH

Question 52

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

Answer 52

carboxylate : 2.3 amino : 9.6

Question 53

what is a zwitterion?

Answer 53

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

Question 54

what is the isoelectric point (pI)?

Answer 54

pH at which the net charge on the ampholyte is 0

Question 55

true or false: pH and pI are equal

Answer 55

true

Question 56

what is an acidic buffer composed of?

Answer 56

weak acid + salt of a strong base

Question 57

what is a basic buffer composed of?

Answer 57

weak base + salt of a strong acid

Question 58

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

Answer 58

pH = pKa or pOH = pKb

Question 59

what is buffer capacity?

Answer 59

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

Question 60

what is the unit of buffer capacity?

Answer 60

moles