pH and buffers Flashcards
how does a pH meter measure the acidity or alkalinity of a substance?
by weighing the hydrogen-ion movement in water-based suspensions
pH is also called? and why is it called that?
potentiometric pH meter because it measures the electrical potential variation between pH electrode and reference electrode
where is the word pH derived from?
“p” is the scientific figure for negative logarithm
“H” is for hydrogen
range of pH?
0-14
equation to get pH?
pH = -log[H+]
who introduced the glass electrode idea?
Fritz Haber and his student Zygmunt Klemensiewicz
who introduced the pH meter? and when
1934 by Arnold Beckam
if the hydrogen density/concentration is greater than the hydroxide density/concentration the solution is?
acidic
pH < 7
if the hydrogen density/concentration is less than the hydroxide density/concentration the solution is?
basic
pH > 7
neutral pH?
7
how many electrodes does a pH have?
2 (measuring and reference electrode)
what is the reference electrode?
has a neutral solution such as KCl with a fixed concentration and gives a stable voltage
what is the measuring electrode?
it depends totally upon the pH of the suspension
what is the algebraic total of the potentials of the measuring and reference electrode, and liquid junction called?
overall potential or voltage
what happens when both electrodes are immersed in the suspension?
ion-exchange happens wherein hydrogen ions flow towards the outer surface of the measuring electrode and displace some metal ions inside
true or false: some of the variation is pH is not negligible therefore produces an unstable voltage
false
where does ion-exchange take place?
inside the surface of the glass electrode to generate a potential variation
what requires calibration to prepare for precise pH measurement?
the voltage studies in the impedance voltmeter
wash the electrodes with what?
distilled water
maintain the sample’s temperature at how much?
25C
true or false: immerse the electrodes and stir the solution to create a homogenous mixture
true
what are the pH meters based on portability?
portable pH meter: compact DC power equipment
desktop pH meter: same as portable
pen pH meter: single scale, conventional measurement range, easy and handy
pH meters based on purpose?
laboratory pH meter: multi-function, high accuracy
industrial online pH meter: excellent stability, steady work, specific level of measurement efficiency, environmental flexibility
pH meters based on advanced level?
economic pH meter
intelligent pH meter
precision pH meter/ digital pH meter
what are the 3 types of electrodes?
glass
reference
combination gel
what are the applications of pH meter?
agricultural industries
measure water quality
chemical and pharmaceutical industries
food industry (dairy products)
detergents
advantages of pH meter?
calibration is low prices and robust
user friendly
reliable and specific
disadvantages of pH meter?
heat affects readings
pH calibration using glass electrodes need to be clean since dirt influences the readings
true or false: most biochemical reactions occur in an aqueous environment
true
why is water highly polar?
bc of its bent geometry
why is water highly cohesive?
bc of hydrogen bonding
how to get pOH?
pOH = -log[OH-]
is an acid a proton acceptor or donor?
donor
is the base a proton acceptor or donor?
acceptor
true or false: [AH] is the conjugate base and [A] is the acid
false, [AH] is the acid and [A] is the conjugate base
true or false: [BH] is the base and [B] is the conjugate acid
false, [BH] is the conjugate acid and [B] is the base
acidic or basic: [H+] > 10^-7
acidic
acidic or basic: [OH-] > 10^-7
basic
what is the physiological pH?
6.5-8.0
how does less pKa affect the pH?
less pKa = more Ka = more acidic
true or false: polyprotic acids can lose more than one proton
true
true or false: each dissociation of polyprotic acids have one Ka and pKa value for all
false, each dissociation has its own unique Ka and pKa
what is the biological definition of a buffer?
solution that resists change in pH when adding an acid or base
what is the chemical definition of a buffer?
mixture of a weak acid and its conjugate base with a buffering range of pKa+ or - 1
buffer pair (WA + CB) when adding strong base will yield what?
CB and H2O
buffer pair (WA + CB) when adding strong acid will yield what?
more weak acid
what are ampholytes?
ionizing groups that have acidic and basic pKa
the ionic form of each compound is dependent on what?
the pH of the solution
if the pH of the solution is greater than the pKa, what form does it take?
conjugate base form deprotonated
if the pH of the solution is less than the pKa, what form does it take?
conjugate acid form protonated
what is the chemical formula for glycine?
H2N - CH2 - COOH
what is the pKa of the carboxylate and amino groups in glycine?
carboxylate : 2.3
amino : 9.6
what is a zwitterion?
ionic form of a substance that has a net charge of 0
what is the isoelectric point (pI)?
pH at which the net charge on the ampholyte is 0
true or false: pH and pI are equal
true
what is an acidic buffer composed of?
weak acid + salt of a strong base
what is a basic buffer composed of?
weak base + salt of a strong acid
when the condensation of the conjugate acid is equal to the conjugate base what happens?
pH = pKa or pOH = pKb
what is buffer capacity?
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
what is the unit of buffer capacity?
moles
