Acids and Bases

Question 1

Factors affecting acid strength - Strength of H-A bond

Answer 1

• As bond strength increases acidity decreases, pKa increases

Question 2

Factors affecting acid strength - Electronegativity of atom bearing negative charge

Answer 2

• As electronegativity increases, acidity increases, pKa decreases

Question 3

Factors affecting acid strength - Inductive effects

Answer 3

• As you add Cl the species becomes more stable (stabilising effect)
• Methyl can destabilise a negatively charged atom

Question 4

Factors affecting acid strength - Electronegativity of atom bearing lone pair

Answer 4

• as electronegativity decreases, basicity increases, pKa increases

Question 5

What is the concept of Henderson Hasselbalch?

Answer 5

• Where pH is equal to pKa, plenty of A- to mop up H+, you’ve got plenty of HA to mop up HO-
• e.g. use a weak acid and it’s salt

Question 6

Factors which affect base strength - availability of the lone pair

Answer 6

• the greater the availability of the lone pair the stronger the base

Question 7

Factors which affect base strength : Stable B+-H

Answer 7

• strong base

Question 8

Factors which affect base strength - High pKa of B+-H

Answer 8

• B is a strong base

Question 9

For a general acid the relationship between pKa and pH is…

Answer 9

Ka = [H3O+][A-] / [HA]

Question 10

For a Henderson Hasselbalch acid the relationship between pKa and pH is…

Answer 10

pH = pKa + log10 x [A-] / [HA]

Question 11

Choosing the right buffer…

Answer 11

• pH range in which you’d perform reaction chose acid in-between and it’s salt (eg 7-9 you’d pick 8)