pH & equilibria Flashcards
Why is pH 7 considered neutral?
How is pH affected by temperature?
What are the symptoms of blood pH at these levels:
>7.5 =
=7.4 =
<7.3 =
As H2O is virtually constant in aq solution, so [H+] = [OH-] = 1x10-14, so [H+] = 10-7
Temperature increase means more vibrations- causing formation of H+ ions. Increase H+ concentration causing pH decrease (more acidic)
alkalosis (hyperventilation)
normal
acidosis (shallow breathing)
On the graph of titrating a weak acid HA, what is the y and x axis?
Where is the pKa on a graph? What is it?
Where is the end point of the titration?
Y = pH (low bottom high top) X = alkali added, closer to crossing of axis is more acidic
where [HA] = [A-] (straight horizontal line)
The pH where those 2 concs are equal
where nHA = nOH-: so the moles of acid are equal to the moles of A-
typically midway up a slope of the line around neutral pH
What is a buffer?
Where is the buffering region in a titration? Why is this significant?
What is an amino acid’s isotonic point? What is its significance?
A weak acid and its conjugate base/salt that shifts equilibrium to accommodate H+ or OH-
Around the pK where [HA] = [A-]. Near the pH values close to its pKa
pH where zwitterion is in aq solution as number of -ve charges equal to number of +ve charges
pH where the protein has minimum solubility (greatest opportunity for oppositely charged groups to attract & cause aggregation and precipitation)
What are 2 ways of measuring pH?
What makes a theoretically best buffering range?
What happens to Gibbs free energy when K = 1, K<1 and K>1
What must Gibbs free energy be in order for a spontaneous reaction? What is its units?
Indicator (different pKs- less precise), pH electrodes
Where the pH change is low (horizontal line) and the buffering capacity is the greatest at the pKa of the buffer solution
K = 1, G = 0 (reaction at equilibrium)
K > 1, G = -ve (reaction favours products)
K < 1, G = +ve (reactants)
Very negative- favour the products and have more energy for reaction. kJmol-1
What are the standard conditions for a standard hydrogen electrode (SHE)? What is the potential generated?
What is an electrode potential Eh dependent on?
Em/midpoint potential is when the reduced species is equal to the oxidised species. What makes a good reductant/oxidant?
Em is under standard conditions of equal concentrations. What is Eh? how do they compare?
1M H+, 1atm H2 and 0V
Redox potential of the species
More negative Em7 = good reductant
Eh is the actual potential generated & depends on the relative conc of the reduced & oxidised species.
If [red] = [ox], Eh = Em
[red] > [ox], Eh < Em
[red] < [ox], Eh > Em
Potentiometric pH measurement:
The glass electrode is connected to a standard reference electrode in the same test solution connected to a voltmeter. What is the glass electrode composed of?
When the electrode is placed in HCl, what happens?
How is the electric potential affected?
Silver wire with silver chloride tip. Inside the glass is potassium chloride buffer solution.
Many H+ from HCl solution will fuse into the outside membrane of the glass bulb, and the H+ on the inside will fuse into the inner membrane. The H+ conc on the outer membrane is higher, and so an electric potential is generated.
The larger the gradient, the larger the electric potential. If the conc on the outside is higher, generates a positive potential. If it’s higher on the inside, generates a negative potential.
