12: Acids, Bases and pH Flashcards
pH Calculations Monoprotic/Diprotic Acids Acids/Bases Kc and Water Kw - Ionic Product of Water Ka - Weak Acids
What is a Bronsted Lowry acid and base?
Acid - Proton donor
Base - Proton acceptor
What is the definition for an acid?
A substance that reacts with water to form H+ ions.
What is the difference between monoprotic and diprotic acids? Give an example of each.
Monoprotic acids donate 1H+ when they dissociate eg: HCl
Diprotic acids donate 2H+ when they dissociate eg: H2SO4
Describe how strong acids dissociate in water.
They dissociate fully into water, meaning nearly all of the H+ ions will be released.
Describe how weak acids dissociate in water.
What is formed during the dissociation of weak acids.
They only dissociate partially, meaning only a few H+ ions are released. This forms an equilibrium, meaning weak acids are usually part of reversible reactions.
Describe proton donation in acid/base reactions.
Protons from the acid (H+) are donated to the base which accepts them.
What happens when acids and water react?
Water acts as an base to accept the proton.
Give the formula for calculating pH using H+ ion concentration.
pH = -log(H+)
Give the formula for calculating H+ concentration from pH.
H+ = 10^-pH
Give the equation for the dissociation of water.
H2O (l) + H2O (l) (reversible) H3O+ + -OH
Give an equation for Kc for the dissociation of water from the previous equation.
Kc = [H+] [-OH]
—————-
[H2O]
What constant is formed if you multiply Kc by H2O?
Give an equation for multiplying Kc and the new constant that forms.
Kc [H2O] = [H+] [-OH]
Kw = [H+] [-OH]
What is Kw?
The ionic product of water. 1x10^-14
Kw can be used to find the pH of which 2 substances?
Pure water.
Strong bases.
What is pure water?
Describe its pH.
A substance that has an equal concentration of H+ ions and -OH ions
Its pH can be 7, but not always.
Root of Kw tells us what? (pure water)
What is the opposite.
H+ concentration.
(H+^2) tells us Kw.
Give the equation linking Kw, H+ and -OH.
Kw = [H+][-OH]
Why is H2O not included in the Kw equation?
H2O is almost constant.
Why does the value of Kw increase as temperature increases?
Give the equation that helps to explain this.
H2O (reversible) H+ + OH-
Equilibrium shifts to the right in the endothermic direction to minimise temperature change.
What is Ka used to calculate?
pH of weak acids.
What is Ka?
The acid dissociation constant.
Give an equation linking Ka, H+, A- and HA, where Ka is the subject.
Ka = [H+] [A-]
————
[HA]
Give an equation linking [HA] to [H+]^2 and Ka, where HA is the subject.
[HA] = [H+]^2
———-
Ka
Give an equation linking for Ka where H+ is the subject.
H+ = ROOT [HA] [Ka]
Give the equation for Ka where A- is the subject.
A- = [Ka] [HA] / [H+]
Give the equation to calculate pKa
pKa = -log (Ka)
Give the equation to calculate Ka.
Ka = 10^-pKa
The bigger the Ka value….
The stronger the acid
The smaller the pKa value……..
The stronger the acid.
