6. Acids and Bases

Question 1

What does the acidity measure? Where does the hydrogen ions come form?

Answer 1

Measures the concentration of hydrogen ions in an aqueous solution

Formed by loss of an electron from a hydrogen atom= Positively charged

Question 2

What is the equation for pH?

Answer 2

pH= -log10 [H+]

The lower the pH, the greater [H+], and the more acid the solution becomes

When [H+] decreases, [OH-] increases as
Kw= [H+] x [OH-]= 10^-14

Question 3

What happens to an acid when it is added to water?

Answer 3

Its [H+] increases as the chemical dissociates

Question 4

What happens to a base when it is added to water?

Answer 4

Its [H+] decreases as it reacts with H+ and [OH-] increases

Question 5

What is Ka and what is its equation?

Answer 5

Ka= The acid dissociation constant
Ka= [H+] [A–]
[HA]

Question 6

What is the Henderson-Hasselbalch equation?

What is it used for?

Answer 6

pH= pKa + log [A–]
[HA]

Predicting the pH for a solution containing a defined ration of [A-] : [HA] from pKa value

Means that pH changes comparatively little over relatively large changes in ratio of [A-]/ [HA]

Question 7

What happens when pH

Answer 7

The PROTONATED form of an amino acid side chain predominates= +ve

Question 8

What happens when pH> pKa?

Answer 8

The DEPROTONATED form of an amino acid side chain predominates= -ve

Question 9

Give an example of how changes in charge on functional groups in biological molecules with pH can alter the functional properties of the molecule as a whole

Answer 9

Oxygen binding by haemoglobin:

The lower the pH in tissues, the more efficient the haemoglobin is at unloading oxygen= Tissues get more oxygen

This is due to the partial structure of haemoglobin chasing:
Aspartate (-ve) and histidine (+ve)= charge-charge interaction changes
Histidine becomes protonated
Favours the tense state of protein= Oxygen cannot bind