Acids and Bases

Question 1

Bronsted Lowry definition of acids and bases

Answer 1

acids are proton donors

bases are proton acceptors

Question 2

Lewis acids and bases

Answer 2

Lewis acids are electron pair acceptors
Lewis bases are electron pair donors.
Lewis acid/base reactions frequently result in the formation of coordinate covalent bonds.

Question 3

strong acid

Answer 3

one that dissociates completely in water

ex) HCl

Question 4

weak acid:

Answer 4

dissociation does not go into completion.

weak acid is HF

Question 5

strength of the acid is directly related to how much the products are favoured over the reactants.

Answer 5

Ka= acid dissociation constant.
if Ka >1 : then products are favoured and we say the acid is strong
if ka<1 : reactants are favoured and the acid is weak.

Question 6

Ka and acid strength

Answer 6

the larger the ka , the stronger the acid.

the smaller the ka, the weaker the acid.

Question 7

what are the common strong acids?

Answer 7

HI
HBr
HCl
HClO4
H2SO4
HNO3
assume that any acid not on this list is weak acid.

Question 8

why is HF weak?

Answer 8

F is smaller then Cl , Br, I
The more stable the conjugate base is the stronger the acid.
larger anions are better ale to spread out their negative charge making them more stable.
HF is the weakest of the H-X acids bc it has the least stable conjugate base, due to its size.

Question 9

we can apply the same ideas to identify weak and strong bases.

Answer 9

Kb= base dissociation constant. the larger the kb the stronger the base and the smaller kb= weaker base.

Question 10

strong bases

Answer 10

group 1 hydroxides ex NaOH
Group 1 oxides Li2O
some group 2 hydroxides BaOH2, SrOH2, CaOH2
Metal amides ex NaNH2

Question 11

weak bases

Answer 11

ammonia NH3, conjugate bases of many weak acids

Question 12

the conjugate base of a strong acid has no basic properties in water

Answer 12

ex) Cl- from HCL

Question 13

the conjugate base of a weak acid is a weak base

Answer 13

ex) F- from HF

Question 14

the weaker the acid the more the reverse reaction is favoured.

Answer 14

and the stronger the conjugate base!

Question 15

the conjugate acid of a strong base has no acidic properties in water

Answer 15

ex ) Li + from LiOH , does not have any acidic properties in water.

Question 16

the conjugate acid of a weak base…

Answer 16

acts as a weak acid! the weaker the base , the stronger the conjugate acid .

Question 17

polyprotic

Answer 17

has more then 1 proton to donate, ex would be carbonic acid H2C03- in its dissociation . HCO3- first acts as a CB then it acts as an acid : therefore that means HCO3- is amphoteric : when a substance can act either as an acid or a base.

Question 18

The ion product constant of water

Answer 18

water is amphoteric , it reacts with itself in a bronzed lowery acid base reaction and produces H3O+ and OH-
this is called self ionization of water.
the equilibrium expression is
kw= [H30+][OH-]
written as Kw : equilibrium expression for auto ionization of water , so kw is the ion-product constant of water.

Question 19

at 25 degrees Celsius what is kw

Answer 19

1 x 10^-14

Question 20

kw varies with?

Answer 20

temperature! like all other equilibrium constants!

Question 21

kw will not be affected by concentration

Answer 21

ex) if we add an acid the [h3o+] will increase, equilibrium will be disturbed and the reverse reaction will be favoured. decreasing the [OH-] . Same thing happens if we increase [OH-], reverse reaction will be favoured. in either case, THE PRODUCT of [H30+] [OH-] will remain equal to kw

Question 22

pH= - log [H+]

Answer 22

[H+] = 10^-pH
since [H+] = 10^-7
ph of water is 7.

Question 23

pOH= -log [OH-]

Answer 23

[OH-] = 10^-pOH

Question 24

Since [H+][OH-] =10^-14 at 25 degrees Celsius.

Answer 24

the values of pH and pOH satisfy a special relationship at 25 degrees Celsius.
pH +pOH = 14

Question 25

rule of thumb about pH calculation

Answer 25

[H+] = y x 10^-n (n is a whole number)

if y is a number between 1 and 10, pH will be between (n-1) and n .

Question 26

in general p of something = - log of that something

Answer 26

so pKa = -logKa

pKb= -logKb

Question 27

larger the Ka , stronger the acid. but p means negative log of something. therefore, LOWER pKa value will mean higher acid strength.

Answer 27

acid with a lower pKa value is stronger acid and therefore

lower pKb value = stronger base

Question 28

for any acid - base conjugate pair at 25 degrees celcius we will have

Answer 28

KaKb = Kw = 1 x 10^-14
as well as
pKa +pKb = 14

Question 29

weak acids come to equilibrium with their dissociated ions. for a weak acid at equilibrium the concentration of undissociated acid will be much greater then the concentration of hydrogen ion.

Answer 29

to get the pH of a weak acid, you need to use the equilibrium expression.
so set it up as Ka= products/reactants
and if Ka is very small means its a very weak acid and not a lot of it dissociated . then we can assume the x part at the bottom is negligible.
when Ka is <10^-4 –> we can assume that the x being added or subtracted is negligible

Question 30

when determining how much base we need to add to an acidic solution or how much acid we need to add to a base , in order to cause complete neutralization, we need the following formula

Answer 30

a x [A] x Va = b x [B] x Vb
a= number of acidic hydrogens per formula unit
b= constant tells us how many H+ ions the base can accept.

Question 31

remember, regardless of the strengths of the acids or the bases…

Answer 31

all neutralization reactions go to completion.

neutralization reactions are exothermic

Question 32

a salt is an ionic compound ! consists of cation and an anion

Answer 32

in water the salt will dissociate into cation and anion and depending on how these ions react with water , the resulting solution will be either acidic or basic or pH neutral.

Question 33

cation of the salt

Answer 33

group 1 cations or larger group 2 cations : don’t react with water .

but the cation will result in acidic solution if its a stronger acid then water : NH4+, be2+, Cu 2+, Zn2+, Al3+, Cr 3+, Fe3+

Question 34

anion

Answer 34

it won’t react with water if its the conjugate base of a strong acid.
but if its stronger base then water it will produce a basic pH ( THAT will be if its a CB of a weak acid).

Question 35

Buffer

Answer 35

a buffer is a solution that resist change in pH when a small amount of acid or base is added. the buffering capacity comes from the presence of a weak acid and its conjugate base - or. a weak base and its conjugate acid in roughly equal concentrations

Question 36

the Henderson hasselbach equation : for any buffer solution containing a weak acid and salt of its conjugate base.

Answer 36

pH= pKa + log ( conjugate base/weak acid)

Question 37

to design a buffer solution

Answer 37

we choose a weak acid whose pKa is close to the desired pH. An ideal buffer solution would have [weak acid]= [conjugate base] , so then ph=pka

Question 38

we can also design a buffer solution by choosing a weak base and salt of its conjugate acid such that the pea of the base is close to the pOH as possible.

Answer 38

the Henderson hasslebach equation would be:

pOH= pKb + log ( conjugate acid/weak base)

Question 39

what is an indicator?

Answer 39

an indicator is a weak acid that undergoes a colour change when its converted to its conjugate base.

Question 40

how do we select our indicator?

Answer 40

select one whose pKa value is convenient for our purposes

rule of thumb (but dosent always work) : an indicator will change colour in the range +/- 1pH unit from the pka

Question 41

acid-base titration

Answer 41

is an experimental technique to determine the identity of an unknown weak acid or weak base by determining its pka or pkb.
- titrations can also be used to determine the concentrations of any acid or base solution.

Question 42

procedure for acid base titration

Answer 42

adding a strong acid or strong base of known identity and concentration - the titrant- to a solution containing a the unknown base or acid. titrant is added in small discrete amounts , the ph of the solution will be recorded.

Question 43

buffering region

Answer 43

where the pH changes very slowly . as the HF= F- concentration for ex.
then the solution will suddenly loose its buffering capability and ph will increase dramatically.

Question 44

acid base equivalence point

Answer 44

when just enough base is added completely neutralize the HF

Question 45

half equivalence point

Answer 45

the pka = pH

Question 46

Polyprotic acid

Answer 46

the titration curve for the titration of a polyprotic acid like H2CO3 will have more than one equivalence point. the number of he equivalence points is equal to the number of ionizable hydrogens the acid can donate.