Acid-base equlibria Flashcards
Define Bronsted-Lowry acid
A species that can donate a proton (proton donor)
What is required for a substance to act as an acid?
The hydrogen atom must carry a slightly positive charge, due to bonding with a highly electronegative atom
Define Bronsted-Lowry base
A species that can accept a proton (proton acceptor)
What is required for a substance to act as a base?
It must contain a lone pair of electrons that it can use to form a dative colvalent bond with the proton
Define conjugate acid-base pair
A pair of reactants and products that can be interconverted by the transfer of a proton
Define conjugate acid
The species formed when a base accepts a proton
Define conjugate base
The species formed when an acid donates a proton
Identify the conjugate acid-base pairs in the following reaction:
HCl(aq) + H₂O(l) ⇌ H₃O⁺(aq) + Cl⁻(aq)
HCl is an acid; its conjugate base is Cl⁻
H₂O is a base; its conjugate acid is H₃O⁺
Define amphoteric substance
A species that can act as both an acid and as a base
Define strong acid
Write the dissociation of HCl
An acid that almost completely dissociates in aqueous solution
HCl(aq) → H⁺(aq) + Cl⁻(aq)
What is the equation used to calculate the pH of a strong acid?
pH = -log₁₀[H⁺]
What is the equation used to calculate the [H⁺] of a strong acid?
[H⁺] = 10⁻pH
Define weak acid
Write the dissociation of ethanoic acid
An acid that only partially dissociates in aqueous solution
CH₃COOH(aq) ⇌ CH₃COO⁻(aq) + H⁺(aq)
What are the assumptions made when using weak acids in calculations?
- [HA]initial = [HA]equilibrium
- The dissociation of water is negligible
What is the general expression for the acid dissociation constant, Ka?
HA(aq) ⇌ H⁺(aq) + A⁻(aq)
Ka = [H⁺] [A⁻] / [HA]
What are the units for the acid dissociation constant, Ka?
mol dm⁻³
What is the equation used to calculate the acid dissociation constant, Ka
Ka = [H⁺]² / [HA]
What is the equation used to calculate the [H⁺] of a weak acid?
[H⁺] = (square root) Ka × [HA]
What is the equation used to calculate the concentration of a weak acid?
[HA] = [H⁺]² / Ka
What is the equations that link pKa and Ka?
pKa = -log₁₀Ka
Ka = 10⁻pKa
What does the pKa value indicate?
The smaller the pKa value, the stronger the acid
What does the Ka value indicate?
The larger the Ka value, the stronger the acid
