Topic 12 - Acid-base Equilibria Flashcards
What is the definition of a Bronsted-Lowry Acid?
Proton donor
What is the definition of a Bronsted-Lowry Base?
Proton acceptor
What happens in acid-base reactions?
Protons are transferred between substances
Describe what happens in the forwards reaction and backwards reaction when HCl dissociates in water
HCl + H2O <=> Cl- + H3O+
In the forwards reaction HCl acts as an acid and donates a proton to H2O. H2O acts as a base and accepts that proton.
In the backwards reaction H3O+ acts as an acid and donates a proton to Cl-. Cl- acts as a base and accepts that proton.
What are the conjugate pairs in the dissociation of HCl in water?
HCl and Cl-
H2O and H3O+
Conjugate pairs differ by…?
H+
How would you describe the conjugate pairs in the dissociation of HCl and water?
HCl is the conjugate acid of Cl-
Cl- is the conjugate base of HCl
H3O+ is the conjugate acid of H2O
What are the conjugate pairs in the dissociation of NH3 in water?
NH3 + H2O <=> NH4+ + OH-
NH3 and NH4+
H2O and OH-
NH4+ is the conjugate acid of NH3
OH- is the conjugate base of H2O
What is the definition of a strong acid?
One that fully dissociates into its ions
What is the definition of a weak acid?
One that partially dissociates into its ions
What type of conjugate pairs do strong acids, strong bases, weak acids and weak bases have?
Strong acids - weak conjugate base
Strong bases - weak conjugate acid
Weak acids - strong conjugate base
Weak bases - strong conjugate acid
What is the definition of pH?
-log(base 10)[H+]
What value do you use to calculate the pH of a solution?
Hydrogen ion concentration
How do you calculate the hydrogen ion concentration from pH?
10^-pH
A high concentration of H+ ions means…?
A low pH
A low concentration of H+ ions means…?
A high pH
A decrease in pH of 1 on the pH scale is equivalent to…?
The concentration of H+ ions increasing by 10 fold
What is the assumption made when strong acids dissociate?
They dissociate fully into their ions, therefore:
Concentration of acid = concentration of H+ ions when dissociated
What is the definition of the ionic product of water?
The product of the molar concentrations of H+ and OH- ions at a specified temperature
What is the value of the ionic product of water equal to at 298K?
1 x 10^-14
Write the equation for the ionic product of water
Kw = [H+][OH-]
How will temperature affect the ionic product of water?
At higher temperatures the forwards reaction, H2O dissociating into H+ and OH- is favoured as the forwards reaction is endothermic. Therefore, the POE shifts to the right and the value of Kw increases. [H+] and [OH-] increase and so the pH decreases.
Vice versa for when the temperatures are lower
What are the units for the ionic product of water?
mol^2dm^-6
If you have [OH-] how do you calculate the pH of the solution?
- Use Kw to find [H+]
- -Log(base 10)[H+]