Buffers

log (2)

0.3

log (3)

0.5

How do you make a buffer with a weak base (2 methods)

1) add the salt of the conjugate acid in roughly equal mole proportions (eg NH3 with NH4Cl) 2) Roughly half of an equivalent of strong acid (eg H3CNH2 and a half equivalent of HCl)

How do you make a buffer with a weak acid (2 methods)

1) add the salt of the conjugate base in roughly equal mole proportions (eg HCO2H with HCO2Na) 2) Roughly half of an equivalent of strong base (eg HOAc with a half eq. of KOH)

What is the range of a buffer using a weak acid and a weak base?

pkA +/- 1

How do you make a buffer with a pH of 5, given that HA has a pKa of 4.7?

Because pH is greater than pKa, this means that the buffer has more conjugated base than the acid. So a buffer with a pH of 5 would have less equivalents of acid to conjugated base. ex: A- with one third equivalent of H3O+ If pH = pKa, then you'd have A- with one equivalent of HA. Ka = [H+]

bicarbonate buffer system

CO2 (g)+ H2O(l)↔H2 CO3 (aq)↔H+ (aq)+HCO3- (aq) -Blowing off CO2 (hyperventilation) decreases levels of CO2 which causes reaction to shift left consuming H+ and reducing H+ in the blood making pH less acidic -mechanism that deals w/ acidemia (excess H+ in blood)

What can you combine a weak acid with to make a buffer?

Equal mole mixture of weak base OR 1/2 equivalent mole of strong base

Bohr effect

If pH was lower than it normally was (normal physiological pH is 7.4), then the hemoglobin does not bind oxygen as well. In other words, the lower the pH, the more Hydrogen ions, the higher the carbon dioxide level and the LESS affinity Hemoglobin has for oxygen. Shift to the right of the curve means that you require a greater partial pressure of O2 to have the same level of O2 saturation of Hb

If the ratio of base to acid in a conjugate pair is 3:1, and the weak acid has a Ka = 1.0E-5, what can be said about the pH of the buffer solution

If the ratio was 1:1, then the buffer would have a pH of 5. Because there is more base in the conjugate pair, the pH must be greater than 5. Because the ratio does not exceed a 10:1 ratio, the pH must also be less than 6 So the pH of this is between 5 and 6

What does neutralization (equivalence point) mean in regards to pH

Neutralization does not mean to make the pH of the solution equal to 7. When the base is stronger than the acid, the neutralized solution is slightly basic, so the pH is greater than 7. When the acid is stronger than the base, the neutralized solution is slightly acidic, so the pH is less than 7 If you use both a strong base and acid, then the neutralized solution has a pH = 7.

Can you make a buffer with HCl and KOH?

No you cannot make a buffer with a strong acid and a strong base.

Retention of CO2

Respiratory acidosis because your body would shift the equation to the right toward acid. Thus a decrease in pH

Loss of CO2

Respiratory alkalosis because your body would shift toward the left to make up for the loss CO2. Thus an increase in pH

How does a buffer with a weak base and acid respond to changes?

They can equilibrate in both the forward and reverse directions of the reaction to absorb any hydronium or hydroxide that may be added to solution

When creating a buffer with a weak base/acid with half equivalent of strong acid/base, buffering occurs

in the region (where pH does not change appreciably) found in the middle area of the titration curve between the starting point and the equivalence point

log(3/2)

log(3)-log(2) = 0.2

Loss of HCO3-

metabolic acidosis because your body would shift toward the right to make up for loss HCO3- thereby creating more H3O+. Thus a decrease in pH

Loss of H3O+

metabolic alkalosis because your body would shift toward the right to create more H3O+ thereby generating more HCO3-, which decreases pH in the body