Weak acids and bases

Question 1

What is the equation for the dissocation constant?

Answer 1

• K_a = [H⁺ (aq)]_eqm [A^- (aq)]_eqm / [HA(aq)] _eqm

Question 2

What does a large value for Ka signify?

Answer 2

• eqm further to the right, more the acid is dissociated, stronger the aicd

Question 3

How are the units for Ka found?

Answer 3

cancelling the units in the expression

Question 4

How is pH of a weak acid found?>

Answer 4

• assume [H+] = [A-]
• therefore Ka = [H+]² / [HA]
• therefore [H+] = √(Ka x [HA])
• -log₁₀ [H+]

Question 5

What is pKa?

Answer 5

• pK_a = -log₁₀ K_a
• measure of how strong a weak acid is
• smaller the value, the stronger the acid.