Acid, Based and Kw - physical Flashcards
(35 cards)
Bronsted lowry acid
proton donor
rele H+ ions when mixed in water
never get H+ alone = combined with H2O to form H3O+ ( hydroxonium ions )
Bronsted lowry base
proton acceptor
grab hydrongen ions
dissociation in water - strong acid
- completely dissociates
nearly all H+ ions = released - strong base also completely ionise
dissociation in water - weak acid
partially dissociates into ions when added in water
- slightly dissociates in water, a small amount of protons is produced
ionic product of water ( Kw )
- how is it formed
water dissociates into hydroxonium ion and hydroxide ions
H2O + H2O = H3O+ + OH-
Kc = (H+)(OH-) / H2O
water only dissociates a tiny amount - equi to left
- so much water compared to ions = concern of water = constant value
Kw = (H+) (OH-)
Kw and when it’s used
- find pH of the strong base
- same value for aq solu at given temp
at 298K = 1.00 x 10^-14 mol2 dm-6
- value changes as temp changes
Kw in pure water
- always one H+ ion for each OH-
so (H+) = (OH-)
Kw = (H+)^2
Ph scale
measure concen of H+ ions
pH = -log10 (H+)
strong acids
HCl
H2SO4 ( sulphuric acid )
strong acid will dissociated more in solution, the concentration of hydrogen ions will be higher, so the ph will be lower
strong bases
NaOH
KOH
calculating (H+)
H+ = 10^-ph
monoprotic acids
monoprotic = each mole of an acid release one proton when it dissociates
- Hcl , CH3COOH (ethanoic acid) and HNO3 = monoprotic
H+ same as concen of acid
diprotic acids
each mole of acid will release 2 protons when dissociates
2 mol of hydrogen ions for each mole of acid
- sulphuric acid = diaprotic
- ethhanediodic aicd = H2C2O4
H+ concern = x2 the acid
Ka
acid dissociation constant
- weak acid only sightly dissociates so [H+]
dissociation of acid much greater than dissociation of water = assume all H+ ions in solu come from acid
Ka = [H+]^2 / [HA]
unit = mol dm-3
pKa and Ka
pKa = -log10 Ka
Ka = 10^-pka
what assumption do you make when calculating Ka for weaka acd, why not true for strong acid
- assumption = weak acid only partly dissociates
so think all the H+ ions came from dissociation of acid instead of dissociation of water.
not true for strong acid because water completely dissociates
would strong acid have higher or lower Kpa and ka
and why
- strong acid have lower Kpa
lower the pKa more stronger the acid - stronger the acid higher the Ka value
higher Ka = indicates greater tendency for acid to dissociate
why indicator added
added to the base to show exactly when the base neutralises the acid
vertical line at the curve
- equivalence point or end point
- at this point tiny amount of base causes sudden, big change in ph ( here is when all the acid is neutralised
how to find dilution of strong acid
org [H+] x old volume/new volume = new [H+]
reaction between weak acid and strong bases
- when weak acid reacts with strong bases
- for every mole of OH- added, one mole of HA is used up and one mole of A- is produced
mol dm-3 to g dm-3
Mr x moles = mass
indicator
- methyl orange = red to yellow ( 3.1-4.4)
- phenolphthalein = colourless to pink (8.3- 10)
acid to alkaline
for weak acid and weak bases = no indicator because change in ph is gradual and not sharp ( very difficult to determine exact point acid is neutralised ) need to use ph meter
titration and diprotic acid
- diprotic acid releases 2H+ ion when it dissociates
- reaction happen at 2 stages = because 2 proton removed from acid separately.
will have 2 equivalent point
when calcu concen of a acid
- 1st concen / 2
