Acids and Bases

Question 1

What do all acids release

Answer 1

H+

Question 2

What do all bases accept

Answer 2

H+

Question 3

Common bases

Answer 3

Metal oxides
Metal hydroxides
Ammonia and amines

Question 4

Alkalis (soluble bases that dissolve in water release in water

Answer 4

OH- ions

Question 5

How are salts made

Answer 5

When H+ from acid is replaced by a metal ion/another positive ion

Question 6

Neutralisation reactions

Answer 6

Acids react with:
carbonates to form CO2
bases (metal oxides) to form H2O
alkalis to form H2O
Metals to form H

Question 7

Redox reactions

Answer 7

Acids react with metals
Metal is oxidised
Hydrogen is reduced

Question 8

Ammonia

Answer 8

Forms weak alkaline solution when dissolved in H2O

Question 9

Salt crystals features

Answer 9

Have water = crystalline form, hydrated
No water = powdered form, anhydrous
Molar proportion of H2O 名前 water of crystallisation

Question 10

Hydrated salt formula

Answer 10

1: calculate n of anhydrous
2: calculate n of H2O
3: determine hydrated salt ormula

Question 11

Titration calculation method

Answer 11

1) find n of compound in the sol
2) use equation to ID mol no. of substances in 2nd sol.
3) ID n for any other relevant substances
4) scale quantities to match
5) calculate M

Question 12

Bronsted-Lowry model

Answer 12

(conjugate) Acid = H+ donor
(conjugate) Base = H+ acceptor
Alkali = base that dissolves in H2O forming OH-

Question 13

Water’s acid-base equilibrium

Answer 13

Ha(aq) ⇌ H+(aq) + A-(aq)

Question 14

Acid strength

Answer 14

Extent to which it dissociates into H+ and A-

Question 15

Strong acid strength

Answer 15

Almost complete dissociation

Question 16

Weak acid strength

Answer 16

Partial dissociation

Equilibrium favours non-dissociated side

Question 17

Ka, acid dissociation constant

Answer 17

Dissociated side/non-dissociated side

Unit = mol dm-3

Question 18

Large vs small Ka

Answer 18

Large Ka = large dissociation, strong acid

Small Ka = small dissociation, weak acid

Question 19

Concentration vs strength of acid

Answer 19

Concentration = amount of acid dissolved in 1dm3 o solution

Strength=dissociation extent

Question 20

pH formula

Answer 20

pH=-log10 [H+(aq)]

Question 21

H+ formula

Answer 21

[H+(aq)]= 10-pH

Question 22

pH value meanings

Answer 22

Low H+ value = high pH value

High H+ value = low pH value

Question 23

pH changed by 1 =

Answer 23

H+ changed by 10x

Question 24

Strong acid pH calculations

Answer 24

Found directly from acid concentration

[H+]=[HA]

Question 25

Weak acids pH calculation

Answer 25

Need acid concentration and Ka value
Consider:
[HA(aq)]equilibrium ≈ [HA(aq)]start
[H+(aq)] ≈ [A-(aq)]

Formula therefore:
Ka ≈ [H+(aq)]2/[HA(aq)]

Question 26

pKa and Ka link

Answer 26

Logarithmic version of Ka

pKa = -log10Ka
Ka = 10-pKa

Low Ka = high pKa
High Ka = low pKa

Question 27

Kw

Answer 27

Ionic product of water

Kw=[H+(aq)][OH-(aq)]

Question 28

Kw at 25 degrees

Answer 28

Kw=1.0x10-14 mol2 dm-6

Question 29

H+ and OH- in water

Answer 29

Same concentrations,
10-7 mol dm-3. Total therefore:
10-14 mol dm-3

Question 30

H+ vs OH- concentrations

Answer 30

Water: H+ = OH-
Acid: H+ > OH-
Alkaline: H+ < OH-

Linked by Kw

Question 31

Strong alkalis pH calculation

Answer 31

1) Find concentration directly from alkali concentration
2) solve for H+ ( Kw/OH-)
3) calculate pH

Question 32

Titration curve features

Answer 32

Mid-point of vertical bit is Equivalence Point

Indicator is only suitable if its pKind value is within the pH range of the vertical part

Question 33

Ka from a titration curve

Answer 33

1) Get vol. of alkali for neutralisation from titearion curve
2) get pH at half-neutralisation fron curve
3) half-neut, HA = A-, so Ka = H+
Ka = 10-pH

Question 34

∆Hneut value

Answer 34

Approximately -57.9kJ mol -1 for strong acids

Less exothermic for weak acids

Question 35

Buffer soluions

Answer 35

Minimise pH changes by removing most of added acid/alkali

Made of HA and its conjugate base

Question 36

Adding H+ to a buffer

Answer 36

H+ is increased
pH change is opposed. Equilib moves left removing H+ and forming HA
A- removes most of added H+

Question 37

Adding alkali to buffer

Answer 37

Added OH- reacts with small concentration of H+
pH change opposed by moving equil to the right, restoring H+ as HA dissociates
HA restores most of lost H+

Question 38

Buffer solution pH depends on

Answer 38

• Ka of buffer system

* ratio of weak acid and its conjugate base

Question 39

Arrhenius acids and bases

Answer 39

Acids: dissociate in water to make H3O+
Bases: dissociate to make OH-

Question 40

Lewis acids and bases

Answer 40

Acid aka electrophile: e- acceptor

Base aka nucleophile: e- donator

Question 41

Acid-conjugate base link

Answer 41

Acids are directly proportional to conjugate base’s stability.
More stable = more acidic

Question 42

Base stability considerations

Answer 42

Larger atoms いい
More electronegative いい
sp hybridised >sp2>sp3 いい
e- withdrawing groups on acid いい
Resonance structures いい

Question 43

pKa values

Answer 43

V strong acids = pKa &<0

Weak acids = pKa 0-9

Question 44

Equilibrium rule

Answer 44

Equilibrium of a reaction will favour side with weaker acids and bases

Question 45

Acid dissociation constant

Answer 45

Ka = [H+][A-]/[HA]

Question 46

Buffer solution pH

Answer 46

pKa + log10 (salt/acid)