ch20 - acids, bases & ph Flashcards
what is the bronsted - lowry definition of an acid and base
acid - proton donor
base - proton accepter
what is the arrhenius definition of an acid and base
aicds - dissociate and release h+ ions in aq solution
alkali - soluble bases releases oh- ions
HCl (aq) + OH- (aq) <–> H2O (l) + Cl- (aq)
what are the conjugate acid-base pairs
HCl (A1) -> proton donor -> Cl- (B1)
OH- (B2) -> proton acceptor
-> H2O (A1)
what are monobasic acids and give examples of them
monobasic: one H+ in acid that can be replaced in acid-base reactions per molecule
(H)Cl
CH3COO(H)
what are dibasic acids and give examples of them
dibasic: two H+ in acid that can be replaced in acid-base reactions per molecule
H2CO3
what are tribasic acids and give examples of them
tribasic: three H+ in acid that can be replaced in acid-base reactions per molecule
H3BO3
write the ionic eq for:
H2SO4 (aq) + Mg (s) -> MgSO4 (aq) + H2 (g)
H2+ (aq) + Mg (s) -> Mg2+ (aq) + H2 (g)
acid + metal -> ?
eg?
acid + metal -> salt + h2
2H+(aq) + Zn(s) -> Zn2+(aq) + H2 (g)
acid + carbonate ->?
eg?
-> salt + water + co2
2H+ (aq) + CO32- (aq) -> H2O (l) + CO2 (g)
acid + base -> ?
eg?
-> salt + water
2H+ (aq) + MgO (s) -> Mg2+ (aq) + H2O (l)
acid + alkali ->
eg?
-> salt + water
H+ (aq) + OH- (aq) -> H2O (l)
what is the relationship b/w pH value and [H+]
low [H+] -> high pH value
high [H+] -> low pH value
whats the mathematical realtionship bwteen pH and [H+]
pH = -log[H+(aq)]
[H+ (aq)] = 10^-pH
a change of one ph number is equal to a *x difference in [H+]
- ten times
what is the pH of a solution with a H+ (Aq) concentration of 2.45*10^-3 moldm-3
pH = -log(2.45*10^-3)
2.61 dp
What is the [H+ (aq)] of a solution with a pH of 8.75
[H+ (aq)] = 10^(-8.75)
for a …… acid [H+ (aq)] is equal to the concentration of the acid [HA(aq)]
strong
the pH of a strong acid can calculated directly from the conc. of the acid
a pH of 1 has x times the conc. of H+ ions as a solution with a pH of 2
x = 10
Ka?
Acid dissociation constant %
The higher the Ka the …….. the acid
Stronger the acid
High Ka -> high dissociation
What is the logarithmic equation for Ka
pKa = -logKa
Ka = 10^-pKa
A stronger acid would have a …….pKa value
Smaller
what is a weak acid
an acid that partially dissociates in solution
what is the Ka equation for a weak acid
Ka = [H+]^2 / [HA]
what are the two approximations that we make when simplifying the Ka equation for weak acids
HA dissociates to produce ‘equal’ equilibrium conc. of H+ and A- (we neglect the small h+ released by water)
neglect any decrease in conc. of HA from dissociation (assume [HA]»_space;> than [H+] eq
how can we determine the Ka for a weak acid experimentally
prepare standard solution of weak acid of known conc
measure pH of solution w/ pH meter
what is Kw and what is its equation
ionic product of water
Kw = [H+(aq)] [OH-(aq)]
what is the importance of having Kw as a set value
sets a neutral point in the pH scale
what is the value of Kw at 298K give the units
1 * 10^-14 mol2dm-6
what is the relationship b/w [H+] and [OH-] when solution:
acid
neutral
alkali
[H+] > [OH-]
[H+] = [OH-]
[H+] < [OH-]
what is the [H+] and [OH-] for a acid solution of pH = 3
[H+] = 10^-3 moldm-3
[OH-] = 10^-11 moldm-3
for monacidic bases each mole of NaOH (eg) releases …. mole of OH- ions
one
What is a buffer solution
A solution that minimises pH changes when small amounts of an acid or base are added.
