acids & bases Flashcards
brønsted–lowry acid
proton donor
brønsted–lowry base
proton acceptor
conjugate acid–base pair
two species that differ by one proton
relative strength relationship of conjugate acid-base pairs
stronger the acid, weaker the conjugate base (if an acid readily donates a proton, its conjugate base does not readily accept it back)
stronger the base, weaker the conjugate acid (if a base readily accepts a proton, its conjugate acid does not readily donate it back)
amphiprotic substance
behaves as a brønsted–lowry acid & base
able to donate & accept protons
(e.g. H₂O)
Ka trend
larger Ka = greater extent of dissociation = stronger acid
smaller Ka = lower extent of dissociation = weaker acid
extent of dissociation trend
(Ka)
greatest for the first dissociation & smaller for each subsequent dissociation
(each acid in the series becomes progressively weaker)
it becomes harder to lose a proton as the acid species becomes more negative
strong acid & base
ionizes completely in aqueous solution
readily donates/accepts protons
high conductivity (more ions)
“→”
strong acids
HCl
HNO₃
H₂SO₄
strong bases
NaOH
Ba(OH)₂
(group I hydroxides in general)
weak acid & base
ionizes partially in aqueous solution
high proportion of undissociated particles
low conductivity (less ions)
“⇌”
weak acids
CH₃COOH
H₂CO₃
(carboxylic acids in general)
weak bases
NH₃
(amines in general)
strength vs concentration
strength refers to the degree of dissociation
concentration refers to the relative amount of solute in a given volume of solution
water characteristics
weak electrolyte
self-ionizes to a very small extent
buffer
solutions that are conjugate in nature & resists changes in pH when small amounts of acid or base are added
until the buffer is exhausted (broken), causing pH change
indicator characteristics
weak acid (HIn) or weak base (BOH)
conjugate acid-base pair (color A & color B)
when does an indicator change colour ?
pKa = pH or Ka = [H⁺]
explain the relationship between the pH range of an indicator & its pKa
pH range : HIn (color A) & In⁻ (color B)
pH = pKa : indicator changes color (Hln = In⁻)
pH < pKa : indicator is color A (HIn > In⁻)
pH > pKa : indicator is color B (HIn < In⁻)
pKa trend
high pKa = low Ka = weak acid
low pKa = high Ka = strong acid
equivalence point
moles of reactants are equal
chemical reaction finishes
end point
indicator changes colour
additional drop of titrant causes sharp change in colour
