Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

MBB 222 > Topic 4 > Flashcards

Topic 4 Flashcards

1
Q

Ionic equilibrium, pH, pKa

A
  • the cell is an aqueous environment
  • water is the main solvent for biological systems
  • water has a slight tendency to dissociate into a hydrogen ion - a proton, H+, and a hydroxide ion (OH-)

H20 <-> H+ + OH-

  • only a small fraction fo the H2O molecules become ionized
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Generalized reaction

A

A + B <-> C + D

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Equilibrium constant Keq

A
  • The degree of dissociation
  • Keq for any given chemical reaction is fixed at a specified temperature
  • defines the composition at equilibrium regardless of the starting concentrations
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Kw

A
  • the ion product constant of water at 25 degrees
  • Kw = 10^-14 M^2
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Can [H+] and [OH-] change?

A

Yes
- if one increases the other will decrease to maintain Kw

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is the basis of the pH scale?

A

Kw

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Regardless of pH

A

[H+][OH-] = 10^-14 M^2
pH +pOH = 14
- the lower the pH, the higher the [H+]

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

pH Scale

A
  • a convient way to express [H+] concentration, pH = -log[H+]
  • the higher the [H+] of a solution (the more acidic), the lower the pH
  • is logarithmic, so a differ ne in 1pH unti is a 10x difference in H+ concentration
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Measuring pH

A
  • indicator dyer
  • colourless in acidic to neutral solutions and pink in basic solutions
  • glass electrode
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Strong acids and bases

A
  • almost completely ionize (dissociate) in aqueous solutions
  • strong acids (HA) will almost completely dissociate into H+ plus their conjugate base
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Weak acids and bases

A
  • hold onto their protons tightly and thus dissociate only partially
  • the equilibrium constant, Ka, of a weak acid is :
    Keq = ( [H+][A-] ) / [HA] = Ka
  • the larger the Ka, the greater the tendency for HA to dissociate
  • as with [H+], because the numbers are very small, for convenience the strength of acids is expressed in terms of pKa, pKa = -log Ka
  • a strong acid will have a large Ka and hence a small pKa
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Henderson-Hasselbalch equation

A
  • describes the relationship between pH and the ratio of acid to base in a solution
  • tell you exactly how much pH changes as you add a base (A-) to an acidic solution or vise versa
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

When [HA] = [A-], pH =pKa

A

The pKa is equal to the pH at which [HA] = [A-] (ie. the concentrations of the acid and the conjugate bases are equal)
- the lower the pKa, the stronger the acid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Titration curves

A
  • allow determination of pKa
  • a plot of the dependence of pH of a solution on the amount of base added
  • let you determine how much weak acid is present in a solution based on the amount of strong base required to neutralize that solution or to bring it to a specific pH
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Titration curve midpoint

A
  • the point where [A-] = [HA] or [proton acceptor] = [proton donor]
  • at this point the pH is equal to the pKa
  • the lower the pKa, the stronger the acid
  • the weak acid and the conjugate bases are present in ~ equal concentrations
  • the HA can neutralize any base added by dissociating to provide more H+ and the A- can neutralize any acid added by associating with excess H+, resulting in minimal pH change within the buffering range
  • weak acids have the highest buffering capacity when the pH is equal to their pKa
  • the weak acid solution acts as a “buffer”
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Buffer

A
  • a mixture of H+ donor and its H+ acceptor
  • have the ability to maintain a relatively constant pH within a certain pH range
  • the pH at which a buffer is most effective will depend on its pKa
  • biological buffers maintins a relatively constant pH within a compartment of an organism which is extremely important for survival
17
Q

Weak acids in biology and medicine

A
  • buffer systems defend cells and organisms against pH changes
  • enzymes have optimal activities at different pHs - small changes can alter their activity
  • some acid-based conjugate pairs have pKas close to physiological pH so can be in a pronated or deprotonated form at physiological pH - act as buffers
  • different enzymes are active at different pHs
18
Q

pH of blood plasma can indicate disease

A
  • normal pH is ~7.4
  • people with sever uncontrolled diabetes have blood pH below 7.4 (acidosis)
  • alkalosis is when the pH is above pH 7.4
  • blood plasma pH is maintained by the carbonic acid/bicarbonate systems
19
Q

Triprotic acid

A
  • phosphoric acid behaves as this
  • 3 ionizable hydrogen atoms
  • each acid has its own pKa

MBB 222 (5 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions