1 pH, acids, bases + buffers Flashcards
what is Mr?
relative molecular mass
what is Ar?
relative atomic mass
define Mr
the mean mass of a molecule of a compound / 1/12 mean mass of a c12 isotope
define Ar
the mean mass of an atom of an element / 1/12 mean mass of a c12 isotope
what is avogadro’s number and what is its definition?
6.022 x 10^23
number of particles in one mole of a substance
what is the triangle for the moles mass and Mr equation?
mass
mol Mr
what is the triangle for the concentration moles and volume equation?
moles
conc vol
what is the general definition of an acid?
a substance that increases the concentration of H+ ions when dissolved in water
what is the general definition of a base?
a substance that increases the concentration of OH- ions when dissolved in water
define a bronsted lowry acid
proton donor
define a bronsted lowry base
proton acceptor
what is a conjugate acid?
species formed when a base gains a proton
what is a conjugate base?
species formed when an acid loses a proton
how do conjugate acids and bases differ?
the conjugate acid always has ONE extra proton more than the conjugate base
what do strong acids do in water?
completely dissociate
what do weak acids do in water?
partially dissociate
describe a strong acids conjugate base
non basic / very weak
describe a weak acids conjugate base
just weak
what do you use to measure pH?
- litmus paper
- indicator
what is the equation for pH?
pH = -log10 [H+]
what is the equation for pOH?
pOH = -log10 [OH-]
how do you calculate Ka?
Ka = [H+][A-] / [HA]
what is Ka?
acid dissociation constant
what is Ka used for?
working out the pH of a weak acid
what is the equation for pKa?
pKa = -log10 [Ka]
what is pKa used for?
working out the strength of a weak acid
how would you work out [H+] if you know the Ka and the concentration?
[H+] = square root of Ka x concentration
define a weak acid / base
not completely ionised in aqueous solution
define a buffer
any solution that resists a change to pH when a small amount of an acid or a base are added
what makes an acidic buffer?
a weak acid and its conjugate base as a salt
what makes a basic buffer?
a weak base and its conjugate acid as a salt
where does an acidic buffer sit on the pH scale?
buffers on acidic side of neutral
where does a basic buffer sit on the pH scale?
buffers on the basic side of neutral
how do you calculate the pH with henderson hasselbalch?
pH = pKa + log10 x [salt] / [acid]
