2.Acids and ph Flashcards
What is a salt?
salts are ionic compounds formed when the H+ ions in acids are replaced by metal IONS or ammonia ions.
What is a base
a proton acceptor
What is an acid
a proton donor (releases H= ions in aqueous solution)
what is a alkali
Releases OH- ions when in a water solution
whys are things classified as a base but not as an alkali?
IF it accepts protons but dosnt dissolve it cant be and alkali because an alkali need to be able to release OH- ions into a solution which cant happen if its insoluble.
Acid + metal oxide —->
Salt + water
Acid + metal (reactive) —->
salt + hydrogen gas
Acid + metal carbonate—->
salt + CO2 + water
Acid + metal hydro carbonate —->
salt + water + CO2
Acid + alkali —->
salt + water
3 types of bases
Metal hydroxides - HO- ion reacts with H+ to from waterMetal Oxides- Ammonia (and organic amino componds)
dilute amodia decolourises which halid ions?
Chloride
conc ammonia decoulourises which halide ions?
Bromide, and Chloride
insoluble compoud + acid is slow becuase ….
only the surface of the compound can react at once.
methyl orange colours
Alkaline-yellowneural(bit more acidic 4ph) -orangeacidic - red
Phenolphthalein colours
acid - colorlessalkali-pink
what is a strong acid?
Completly disassociates in aqeuous solution
what is a weak acid
partially disasociates in aqeuous solution
what must be present for a something to act as an acid?
a base, as a H+ ion cannot exist on its own
what is a conjugate base?
a species formed when a proton is removed from an acid
(has the possibility to revert back to acid by accepting a proton)
what is a conjugate acid?
a species formed when a proton is added to a base
(has the possibility to revert back to a base by losing a proton)
acid-base pair
a pair of two species that transform into each other by the loss/gain of a proton
can be labled 1.acid,1conjugate base etc
ph=
-log[H+]
[H+]=
10-ph
strong alkali
1 OH- per alkali molecule
Kw=
ionic product of water
[H+][OH-] = 1x10-14
effect temperature has on water’s ph and Kw
H2O <=> H++OH- is endothermic
inc temp = shift right = Kw increase = lower Ph
however the solution is still neautral as [H+]=[OH-]
Ka =
acid disociation constant for weak acids
[H+][A-]/[HA]
=10-Pka
pKa =
-log Ka
what does H3O+ represent
hydronium ion or H+ in aq sol
what values of pka and ka for a strong acid?
small pHa and a high Ka
approximation made in calculating weak acid ph
equ [HA] = initi [HA] as very little disasociates
([HA]-x=[HA]
sig figs for ph
2.21 is 2 sig figures which is the best numebr to give them to
setup for ph calcs
HA <=> H+ + A-
Initial: [HA] 0 0 .
Initial: [HA] (-x) x x .
ingnor -x
0 is replaced witht he conc in buffes
What is a buffer solution
a solution which resists(minimises) changes in ph , upon an addition of small amounts of acid or alkali
a mixture of a weak acid and its conjugate base
2 ways to make a buffer solution
- Add a weak acid and a salt of the weak acid(conjugate base)
- Add excess weak acid to an aqueous alkali.
how to lay out buffer solution questions
- Equilibrium equation
- Effect upon adition of H+ , what it reacts with where the equ shifts to
- Effect upon adition of OH- , what it reacts with where the equ shifts to
an example of a buffer in nature?
blood
H2CO3<=>H+ + HCO3-
what is the equivelance point
the point in a titration at which the volume of one solution has reacted exactly with the volume of the second solution.
what is the endpoint?
the point in a titration at which there are equal concs of the weak acid and conj base forms of an indicator.
what is an indicator
usually a weak acid , with two different colours for its acid and conj base.
indicator equation
HIn <=> H+ + In-
indicator for weak acid/strong base?
phenolphthalein
indicator for weakbase/strong acid
methyl orange
how is an indicator chosen?
the ph value of the end point is as close to the equivelance point as possible. (or on nthe vertical section) so that one drop will change its colour
indicator for weak acid / weak base
none as there is no vertical section so colour change is too gradual
titration curves
what is enthalpy change of neutralisation?
the energy change that accompanies the neutralisation of an aqeuous acid by an aqeuous base to form one mole of water under standard conditions
weak vs strong acid enthalphy of nutralisation
weak acid have less exothermic enthalphys oif neutralisation as some energy is used in breaking hydrogen bongs (in things like carboxillic acids)
