Buffers

Question 1

Definition of Buffer Solution

Answer 1

A buffer solution is a system that minimizes pH changes on addition of small amounts of an acid or a base.

Question 2

How to for a buffer?

Answer 2

To form a buffer, combine a weak acid with its salt, or by adding excess weak acid (HA) to a solution and then neutralizing it with a strong alkali

Question 3

Role of Weak Acid and Conjugate Base in Buffer Action?

Answer 3

The weak acid resists a decrease in pH by donating protons, while the conjugate base resists an increase by accepting protons.

Question 4

How to calculating pH of a Buffer Solution?

Answer 4

pH = pKa + log([A⁻]/[HA]), where [A⁻] is the concentration of the conjugate base, [HA] is the weak acid concentration, and pKa is the acid dissociation constant.

Question 5

How is blood ph regulated?

Answer 5

In blood, CO2 forms carbonic acid (H2CO3), which dissociates into HCO3⁻ (hydrogencarbonate) and H⁺ ions, helping maintain blood pH.

Question 6

What two components does a buffer solution contain?

Answer 6

An acid buffer solution contains a weak acid and its conjugate base.

HA = H+ + A- weak acid conjugate base

Question 7

How can a weak acid buffer solution be prepared from a weak acid and its salt?

Answer 7

A buffer solution can be prepared by mixing together

a solution of a weak acid
a solution of a salt of the weak acid

Question 8

How can a weak acid buffer solution be prepared by partial neutralisation?

Answer 8

A buffer solution can be formed by adding togther

an excess of a weak aqueous acid
and a solution of aqueous alkali

Question 9

In a buffer solution, what occurs to increase pH when acid is added?

Answer 9

[H+] increases
H+ ions react with conjugate base A-
Equilibrium shifts to the left removing most H+ ions

H+ + A- = HA

Question 10

In a buffer solution, what occurs to decrease pH when alkali is added?

Answer 10

[OH-] increases
H+ ions react with OH-
HA dissociates, shifting equilibirum to the right to restore H+ ions

Question 11

When is a buffer solution most effective?

Answer 11

Equal concentrations of the weak acid and its conjugate base.

Question 12

A buffer solution is most effective with equal concentrations of weak acid and its conjugate base
Why is this the case?

Answer 12

The pH of the buffer solution is the same as the pKa value of HA.
Operating pH is typically over two pH units, centred at pH of pKa value.

Question 13

whats the expression of Ka for a weak acid buffer solution?

Answer 13

Ka= [H+(aq)][A-(aq)] / [HA(aq)]

Question 14

How can the pH of a buffer solution be calculated?

Answer 14

When Ka, [HA] and [A-] are known:

Ka=[H+][A-]/[HA]

Question 15

How is pH calculated if [A-]=[HA]?

Answer 15

Ka=[H+] as [A-] and [HA] cancel out in the equation

pKa=pH

Question 16

What is the Henderson-Hasselbalch equation for calculating pH?

Answer 16

pH=pKa + log([A-]/[HA])

Question 17

Where does blood pH operate between?

Answer 17

7.35 and 7.45

Question 18

What happens if the blood pH falls out of the right range?

Answer 18

Below - acidosis causing fatigue, shortness of breath and in extreme, death.
Above - alkalosis causing musle spasms and nausea.

Question 19

What is the most important buffer system in blood?

Answer 19

Carbonic acid-hydrogencarbonate
(H2CO3/HCO3-)

H2CO3 is carbonic acid and is the weak acid
HCO3- is the conjugate base of H2CO3

Question 20

What is the equilibrium for the buffer system in blood?

Answer 20

H2CO3(aq) = H+(aq) + HCO3-(aq)

Question 21

When acid is added to blood, what happens?

Answer 21

[H+] increases
then H+ ions react with HCO3-
then Equilibrium position shifts to the left removing most of the H+ ions

Question 22

When alkali is added to blood, what happens?

Answer 22

[OH-] increases
H+ ions react with OH- ions
H2CO3 dissociates to restore H+
Equilibrium shifts to the right

Question 23

What are the significant points on a pH titration curve?

Answer 23

At first, excess of acid, pH increases slowly.
Vertical section, pH increases rapidly on addition of very small volume of base.
Equivalence point, centre of the vertical section.
At the end, excess of base, pH increases slowly.

Question 24

What is the equivalence point?

Answer 24

The volume of one solution that exactly reacts with the volume of the other solution.

Question 25

What is an acid-base indicator?

Answer 25

An acid-base indicator is a weak acid, HA, that has a distinctively different colour from its conjugate base, A-.

Question 26

when is the end point of a titration?

Answer 26

At the end point of a titration

1) there are equal concentrations of HA and A-
2) the colour is a mix between the extreme colours

Question 27

what are methyl oranges colours?

Answer 27

methyl orange is
red in acid
yellow in alkali
orange at the end point

Question 28

what does a strong acid vs strong base titration curve look like? what indicators are suitable?

Answer 28

it starts low cause it a strong acid and ends high cause its a strong base

Question 29

what does a weak acid vs strong base titration curve look like? what indicators are suitable?

Answer 29

starts higher because its a weak base and it ends higher cause its a strong alkali

Question 30

what does a strong acid vs weak base titration curve look like? what indicators are suitable?

Answer 30

starts low as its a strong acid and ends low as its a weak base

Question 31

what does a weak acid vs weak base titration curve look like? what indicators are suitable?

Answer 31

its starts high as its a weak acid and ends low as its a weak base and there’s not much change

Question 32

When is an indicator suitable for a titration?

Answer 32

The pH indicator range is passed through by the vertical section of the pH titration curve.