acids and bases Flashcards
bases soluble in water
are alkalis
zinc hydroxide
Zn(OH)2
acid definition
any substance that adds H+ ions to water
-proton donor
hydronium ions
hydrogen atoms attach to h2o molecule to form H30
base definition
proton acceptor
weak acids
only a few molecules dissaaociste into ions
strong acids
molecules completely dissociate into ions
strong base
fully dissociate
weak bases
react with water to form equilibrium with h2o
conjugate acid
base plus h+
conjugate base
acid reacting with base and donating proton
equation for concentration
moles of ion concentration/ volume of solution
pH =
-log10(H+)
increasing conc if acid
decreases pH value
pH of strong acid
-log10(H+)
conc of strong acid
(H+) = 10-pH
moles with conc and volume
conc times volume
acid solution + aqueous base when calculating new pH
find change in volume
-find change in (H+)
Kc =
products over reactants
Kw =
H+ times OH-
units mol 2 dm-6
equation for dissociation of water
H2O – H+ + OH-
Kw at room temp
1 times 10-14
temperature effect on kW
decreases if H and OH decrease and if conc of H and OH increase it increases
why does Kw change when temp increases
because equilibrium shifts to right so conc of H and OH produced increases so larger number brings value of Kw up and goes down if conc decreases
-position shifts to right because ionisation of water endothermic
how to find conc of H+ ions in equation
-H and OH equals H squared
-to find H conc you have to square root KW value
why is pure water always neutral
hydrogen ions always equal to amount of hydroxide ions
how to work out conc of OH or H when kW given and one other concentration given
Kw divided by other concentration
what doesnt affect Kw value of pure water
conc of H and OH ions
-addition of base to water
-addition of acid to water
pH
finding pH of strong acid
-log10 H+
finding pH of strong base
-first find the concentration of OH ions using dissociation equation
-find conc of H+ of ions
-use Kw to find it - rearrange equation of Kw
-
dissociation of NaOH
NaOH = Na+ + OH-
calculating conc of strong base
use pH to find conc of H ions
-10-ph
-use Kw to find conc of OH ions
-OH = Kw/ H+
pH and group 2 hydroxides
times by 2 because 1-2 ratio
solubility going down group 2
increases
factors that affect pH of solution
amount of dissociation
-solubility
-concentration of H+ ions
-temperature
calculating what mass of molecule dissolved into water
-use pH to find conc of solution
–logH+
-then OH= Kw/ H+
-rearrange to get moles= conc times volume
-mass= moles times molar mass
calculating final pH of two solutions
-find moles of both compounds
-which one is in excess- calculate limiting compound leftover after reaction
-find conc of limiting in final solution
-use Kw to find conc of opposite ion in final solution
-use conc to find pH
whats a buffer
resists change in pH when small amounts of acid are added to it or base
what must buffer solutions have
high concentrations of undissociated acids and high concs of its conjugate base
exam question how does a buffer resist changes in pH upon addition of a small amount of acid
write down reversible reaction for specific buffer
state that adding acid increases H+
state that equilibrium shifts to the left to lower the conc of H+
state that overall H+ remain almost constant
exam question how does a buffer resist changes in pH upon addition of small amount of base
write down reversible reacrtion for specific buffer
state that reacrion takes place between OH- and H+ which lowers the conc of H+ ions in buffer solution
state that equilibrium shifts to right to replenish lost H+
state that overall H+ remains almost constant
use of buffers in real life
brewing of beer
blood- hydrogencarbonate
swimming pools
alkaline buffers
weak base and conjugate acid
pH below 7
