Acids and Bases Flashcards
define a bronsted-lowry acid
it is a proton donator/H+ donor
define a bronsted-lowry base
it is a proton acceptor/H+ acceptor
define a amphiprotic species
it is a species that is able to both donate and accept a proton, and thus able to react both as an acid and a base
define a amphoteric species
a species that can act as both acid and base
what is a dative bond
where both the valence electrons from a molecule is donated to the bond
is H+ the same as H3O+
yes
HCl + NH3 ––> NH4+ + Cl-
what is the acid and the conjugate base?
HCl = acid
Cl- = conjugate base
acid + base ––>
salt + water (H20)
what are alkalis?
- substances which form OH- ions in solution when they dissolve
- soluble bases
- all alkalis are bronsted-lowry bases
- but not all bronsted-lowry bases are alkalis
what colour is litmus in acid
red
what colour is litmus in base
blue
what colour is methyl orange in acid
red
what colour is methyl orange in base
yellow
what colour is phenolphthalein in acid
colourless
what colour is phenolphthalein in base
pink
acid + metal ––>
salt + hydrogen
acid + carbonate ––>
salt + water + carbon dioxide (CO2)
acid + metal oxide (base) ––>
salt + water (H2O) (ionic, made up of ions)
equation for pH
pH = –log [H3O+]
or
pH = –log [H+]
what units does pH have
none
[H+] =
10^(–pH)
what does a one unit change in the pH mean
there has been a 10-fold change in [H+]
what does a change from pH 7 to pH 11 mean in terms of [H+]?
40x decrease in [H+]
[H3O+]*[OH–] =
Kw
what is [H+] best written as?
[H3O+]
what is the pH a measure of
the concentration of [H+]
what happens at pH 7 (in terms of the concentration of [H30+] and [OH–])
there is equal amounts of [H3O+] and [OH–], it is neutral
in acids, there are _____ [H+] ions than [OH-]
more
in bases, there are _____ [H+] ions than [OH-]
less
when neutral, [H3O+] ____ [OH–]
equals
Kw =
10^(–14) = [H3O+]*[OH–] at (25ºC)
what are the units for concentration
moldm^(-3)
what concentration is considered a concentrated acid?
anything above 1moldm^(-3)
> 1moldm^(-3)
what is the definition of a concentrated acid
an acid that doesn’t have acid like properties
ie. it doesn’t turn litmus paper red, do not release hydrogen gas from metals, do not release carbon dioxide from carbonates etc.
what does the size of Kw tell us about the ionisation of a compound/molecule?
- a small value represents that the reaction has mostly reactants
- a large value represents that the reaction is mostly products
- therefore there is are ions when Kw is larger vice versa
what is Kw?
it is the ionic product of water
pH+pOH =
14
what is the definition of a dilute acid
an acid that is in water and has dissociated into H3O+ ions to give acid like properties
H3O+ is:
- what turns litmus red
- releases CO2 form carbonates
- makes excellent electrical conductors
definition of strong acids
strong acids ionise completely in solution
they transfer all of their protons to water
(H2O + H+ ––> H3O+)
what size is the equilibrium constant when acids are strong? and what does it tell you about the position of the equilibrium?
large and the equilibrium lies to the right
definition of weak acids
- weak acids will transfer a few protons to water
- only a small portion of acid will turn into ions, most will remain as molecules
what do weak acids have?
carbon
how do you identify a weak acid?
carbon is present in the acid
what size is the equilibrium constant when acids are weak? and what does it tell you about the position of the equilibrium?
the equilibrium constant is small and it lies to the left because it is mostly reactants
how do you write a Ka expression for
CH3COOH + H2O ––> CH3COO– + H3O+
Ka= products / reactants
= [CH3COO–] [H3O+] / [CH3COOH]
you do not include liquids in K expressions
definition of weak base
- it doesn’t ionise fully
- it only ionises partially
- equilibrium lies to the left
- Kb value is low/small
definition of strong base
- it ionises fully
- equilibrium lies to the right
- Kb value is high/large
strong acids and bases do what?
they completely dissociate/ionise in water
weak acids and bases do what?
they only partially dissociate/ionise in water
10molL^-1 HCl = a _________ of a __________ acid
fill in the gaps
- concentrated solution
- strong
what is acid deposition
how to put acid in an environment
what are some causes of acid deposition
- wet acid deposition
- rain
- snow
- sleet
- hail
- fog
- mist
- dew
all fall to the ground as aqueous precipitates
- dry acid deposition
- acidifying particles
- gases fall to ground as dust, smoke
these later dissolve in water to form acids
what is the pH of normal rain
5.6 (rain is naturally acidic)
what counts as acid rain?
any rain that has pH below 5.6 (normal rain)
what are the primary pollutants to acid rain
oxides of sulphur and nitrogen
is acid rain a primary or secondary pollutant
secondary as it is produced when acidic gases (oxides of sulphur and nitrogen) are dissolved in water
how is sulfur dioxide produced
burning fossil fuels
produces H2SO3 or H2SO4 when dissolved in water, which are strong acids
how is nitrogen oxides produced
internal combustion engines
produces HNO3 and HNO2 when dissolved in water which are strong acids
what are the effects on acid deposition
- impact on materials
- impact on plant life
- impact on water
- impact on human health
how can we reduce SO2 emissions
pre-combustion methods:
- remove the sulfur present in coal or oil before combustion
- hydrodesulfuristion, catalytic process which removes sulphur from refined petroleum products by reacting it with hydrogen to for hydrogen sulphide: H2S
post-combustion methods:
- flue-gas desulfurisation, removes up to 90% of SO2 from flue gas before it is released into the atmosphere. uses wet slurry of CaO and CaCO3 which reacts with SO2 to form neutral product: CaSO4
how can we reduce emissions that cause acid rain in general?
lower the demand for fossil fuels: use more efficient energy transfer systems, public transport, and switching to renewable energy sources are all ways of reducing emissions
how can we reduce NOx emissions
- catalytic convertor in vehicles, catalyst converts toxic emissions into relatively harmless products
- lower temperature combustion, the formation of nitrogen monoxide is reduced at lower temperature
what is a lewis acid
an electron pair acceptor (electrophile, electron-deficient)
what is a lewis base
an electron pair donator (nucleophile, electron-rich)
what is a dative covalent bond
where one atom donates both electrons to the bond
what bonds are lewis acid-base reactions
covalent, which will always be dative
are all bronsted-lowry acids lewis acids or are all lewis acids bronsted-lowry acids
all bronsted-lowry acids lewis acids but not all lewis acids are bronsted-lowry acids
pH =
– log [H30+]
[H3O+] =
10^-Ph
pOH =
– log [OH–]
[OH–] =
10^-pOH
pH + pOH =
14
pH + pOH =
pKw
Kw = in terms of [H3O+] and [OH–]
[H3O+] [OH–] = 10^ (–14)
Kw = in terms of Ka and Kb
Ka x Kb
pKw = in terms of pH and pOH
pH + pOH = 14
pKw = in terms of pKa and pKb
pKa + pKb
do you include liquids in K expressions
nonononono
the stronger the acid, the ________ the pKa value
lower
they are inversely propotional
what assumptions are you making when calculating the pH of weak acids
eg. ants contain formic acid (HCOOH). At concentration of 0.01mol L^(-1), what is the pH of squashed ant? pKa = 3.75
[HCOO–] = [H3O+]
- ignore [H3O+] from water because this is negligible
[HCOOH] = 0.01 mol L^(–1)
- because hardly any of the HCOOH has reacted
for weak acids, what does [H3O+] =
…___________
√ [acid/HA] x Ka
what assumptions are you making when calculating the pH of weak acids
eg. the ammonia you wash windows with has a concentration of 0.1mol L^(–1). What is its pH? pKa(ammonium ion) = 9.24
[NH4+] = [OH–]
- ignore [OH–] from water because this is negligible
[NH3] = 0.1mol L^(–1)
- because hardly any of the NH3 has reacted
what is the conjugate base of H2CO3
HCO3–
what is the conjugate acid of HSO4–
H2SO4
the stronger the acid (___ pKa), the weaker the conjugate base (____ pKb)
low pKa
high pKb
the weaker the acid (____pKa), the stronger the conjugate base (___pKb)
high pKa
low pKb
the stronger the base (____pKb ), the weaker the conjugate acid (___pKa)
high pKb
low pKa
the weaker the base (____pKb), the stronger the conjugate acid (____pKa)
low pKb
high pKa
what is the relationship between Ka and pKa
inverse, so high Ka means low pKa vice versa
what is the relationship between Kb and pKb
inverse, so high Kb means low pKb vice versa
what is the definition of a buffer
an aqueous solution consisting of a weak acid and its conjugate base (or a weak base and its conjugate acid) that resists changes to pH when small amounts of acid or base are added
how do you make a buffer solution
- mixing roughly equal amounts of a weak acid and its conjugate base
or - partially neutralising a weak acid with a strong base, so that some of the weak acid remains and the rest has been converted to its conjugate base
Strong acids produce n_______ a______
neutral anions
this refers to the ability of the species to react further
eg: HCl ––> Cl– + H+
=> will not react further
strong bases produce n________ c_______
neutral cations
this refers to the ability of the species to react further
eg: NaOH ––> OH– + Na+
=> will not react further
how do buffers keep the pH constant?
they react away any extra acid or base that is added to the solution by reacting them with a strong acid/base conjugate.
they are in an equilibrium reaction so it works according to Le Chatelier’s principle
when does the equivalence point happen
when n(acid)=n(base)
on graph:
half-way up the point of inflection
Why does the point of inflection happen
in most titrations, it is found that a big jump in pH occurs at the point of inflection
Study the graphs in your booklet, pg 47
what are indicators
they are very weak acids that have a different colour to their conjugate bases
where is the buffer region in a graph
the flattish region of the titration curve (where the pH is hardly changing)
at half way to the equivalence point, pH=
pH=pKa(weak acid)
where does the equivalence point occur for a:
strong acid weak base
pH=7
where does the equivalence point occur for a:
strong acid weak base
pH<7
where does the equivalence point occur for a:
weak acid strong base
pH>7
where does the equivalence point occur for a:
weak acid weak base
pH=7
what is hydrolysis
it is a proton transfer
how to remember:
[H+] is also known as proton
for every titration, there are at least two steps: Neutralisation and hydrolysis; explain these two steps
- neutralisation: eg.
acid + base ––> salt + water
- exist as ions in solution and will either do hydrolysis - hydrolysis:
proton transfer
