Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

IB Chemistry HL > Chapter 8/ 18 > Flashcards

Chapter 8/ 18 Flashcards

Acids and bases

You may prefer our related Brainscape-certified flashcards:
Periodic Table flashcards Chemistry 101 flashcards AP® Chemistry flashcards Organic Chemistry 101 flashcards
1
Q

Bronsted-Lowry acid

A

Donates a proton (is a proton donor)

- all contain hydrogen as they must be able to donate a hydrogen ion to another species

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Bronsted- Lowry base

A

Accepts a proton (is a proton acceptor)

- all must have a lone pair of electrons to form a bond w/ the hydrogen ion donated to them by B-L acid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Proton

A

Refers to a hydrogen ion (H+) which exists as the hydronium ion (H3O+) in aqueous solution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Amphiprotic

A

Species that are able to act as either a Bronsted-Lowry acid or a Bronsted-Lowry base depending on what it is reacting with eg. water

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Classification of acids

A

Can be monoprotic, diprotic or triprotic depending on no. of hydrogen ions they release into solution

  1. Hydrochloric acid and nitric acid = monoprotic acids
    - release only one hydrogen ion in solution
  2. Sulphuric acid = diprotic acid
    - releases two hydrogen ions in solution

NB/ ethanoic acid is monoprotic despite having 4 hydrogen atoms
- only one of these is released when ethanoic acids dissociates in solution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Alkali

A

Bases that are soluble in water

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Reaction at equilibrium

A

Reversible reactions
- when a reaction can occur in both directions w/ forward reaction occurring at same rate as reverse reaction = reaction is at equilibrium

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Conjugate acid-base pair

A

A pair that differs by a proton (H+)

Conjugate acid of a base: add one proton (H+)
- have one more positive charge

Conjugate base of an acid: remove one proton (H+)
- have one less positive charge

Charge on the species must have changed as protons have a positive charge

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Amphiprotic species

A
  • a species that can act as both a Bronsted- Lowry acid and a Bronsted-Lowry base depending on what it’s reacting with
  • amphiprotic refers to Bronsted-Lowry theory ONLY
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Amphoteric species

A

Refers to substances that can act as either acids or bases

- use isn’t limited to Bronsted-Lowry

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Acid reactions with metals

A

acid + metal –> salt + hydrogen gas

- unreactive metals (those below hydrogen in the activity series) don’t react w/ dilute acids

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Test for hydrogen gas

A
  • ignite a small volume of gas in an inverted boiling tube

- flammable gas burns w/ a distinctive sound, known as a ‘squeaky pop’

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What are some bases?

A

Metal oxides
Metal hydroxides
Aqueous ammonia

NB/ alkalis are soluble bases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Neutralisation reactions

A

Metal oxide + acid –> salt + water

Metal hydroxide + acid –> salt + water

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Acid reactions with metal carbonates/ hydrogencarbonates

A

Metal carbonate + acid –> salt + water + carbon dioxide

Metal hydrogencarbonate + acid –> salt + water + carbon dioxide

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Test for carbon dioxide

A
  • tested for by bubbling the gas through limewater [an aqueous solution of calcium hydroxide Ca(OH)2 ]
  • if CO2 is present, limewater turns a ‘milky’ colour as a solid precipitate of calcium carbonate is formed
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Neutralisation reactions

A

An acid reacts w/ a base (or an alkali) to produce a salt and water

  • reaction between an acid and a base is exothermic
  • heat is released, enthalpy change is negative
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Equation for a neutralisation reaction

A

Acid + base (or alkali) –> salt + water

NB/ salt produced in the reaction depends on the parent acid and base that react

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Antacid tablets

A

Ease symptoms of excess stomach acid that causes indigestion or heartburn

  • active ingredients of most antacid tablets: metal carbonates or hydrogen carbonates or insoluble metal hydroxides
  • react with excess stomach acid in neutralisation reactions to relieve symptoms of heartburn
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Acid-base titration

A

Determines unknown conc. of an acidic or a base solution using a solution of known conc. (standard solution)

  • an acid-base indicator is used to determine point where acid neutralises the base or vice versa
  • indicators are chosen due to their bright and easily identifiable colour changes
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Method for an acid-base titration

A
  • burette is filled w/ alkali of known conc. (titrant)
  • titrant is added to acid of unknown conc. (analyte) until end-point is reached
  • end point is signified w/ use of an indicator
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Thermometric titrations

A
  • can be carried out using a simple calorimeter
  • heat is released when an acid and base react together- exothermic reaction
  • enthalpy change that occurs = enthalpy change of neutralisation
  • it is the enthalpy change when one mole of water is formed in the reaction of an acid and a base
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Strong acid + strong base reaction

A

When any strong acid + strong base react together, enthalpy change = -57 kJ/mol

  • because net reaction is the same
  • one mole of water is being formed from one mole of H+ ions and one mole of OH- ions
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Define pH

A

pH of a solution = a measure of the conc. of hydrogen ions [H+] in a solution

pH = -log[H+(aq)]

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

pH scale

A
  • an inverse scale
  • higher the conc. of H+ ions in solution, lower pH value
  • lower the conc. of H+ ions, higher the pH value
  • scale is logarithmic to base 10 (change of 1 pH unit corresponds to 10x change in Hydrogen ion conc.)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

pH and conc. of hydroxide ions

A
  • higher conc. of OH- ions = higher pH value

- lower conc. of OH- = lower pH value

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

Acids and alkaline solutions

A

Water

  • [H+] = [OH-]
  • pH = 7
  • neutral solution

Acid solution:

  • [H+] > [OH-]
  • pH lower than 7
  • litmus turns red

Basic solution:

  • [OH-] > [H+]
  • pH higher than 7
  • litmus turns blue
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

Calculating conc. of H+ ions in a solution from its pH value

A 
pH = -log [H+(aq)]
[H+] = 10^-pH
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

pOH of a solution

A

pOH = -log[OH-]

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

Acid-base indicator

A

A weak acid or a weak base in which the dissociated and undissociated forms have different colours
- depending on conc. of H+/OH- ions in solution, one colour or the other is shown

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

Litmus paper

A
  • a common indicator (can’t be used to determine a pH value for a solution)
  • a qualitative indicator
  • made from a natural source, lichens
  • in acidic solutions, litmus appears red
  • in alkaline solutions, litmus appears blue
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

Methyl orange

A

Acid: red
Alkali: yellow

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

Phenolphthalein

A

Acid: colourless
Alkali: pink/purple

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

Universal indicator

A

A mixture of indicators that produces different colours in solutions of different pH
- pH of aqueous solutions can be measured using universal indicator as either a solution or in paper form

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

Indicators

A

May be used to measure pH of a solution

- makes use of the fact that their colour changes w/ pH

36
Q

pH meter

A

Produces a more accurate method of measuring pH, provided they’re correctly calibrated

  • electrode of pH meter is placed in solution to be tested
  • a voltage is generated that’s converted into a pH meter reading displayed on the screen
  • pH meter is calibrated using buffers of known pH, usually of pH 4.0, 7.0 and 10.0
37
Q

Water as a conductor

A

Pure water is a v. poor conductor of electricity

  • means it must have a low conc. of mobile ions responsible for electrical conductivity of solutions
  • water molecules do dissociate (or ionise) to a v. small extent
  • conc. of water is constant
38
Q

Ionic product constant of water

A

Kw = [H+][OH-]

  • Kw is temp. dependent
  • so, at a certain temp., product of [H+] and [OH-] is a constant
  • so, as [H+] of a solution increases, [OH-] decreases
  • neutral solution has a [H+] = [OH-]
39
Q

Strong acids and bases

A

For a strong acid or base, [H+] or [OH-] is equal to its conc.
- because strong acids and bases are completely ionised in solution

40
Q

Strength of an acid or base

A

Acids and bases can be classified as strong or weak

  • strength of an acid/ base refers to its degree of dissociation in aqueous solutions
  • strong acids and bases completely dissociate in solution
  • weak acids and bases only partially dissociate in solution
41
Q

Dissociate

A

Means to break apart an ionic compound into its constituent ions

42
Q

Concentrated solutions

A

Have a high concentration, measured in mol/dm^3

43
Q

Strong acids

A

When a strong acid dissolves in water, it completely dissociates into ions
- all molecules of acid react w/ water to produce hydronium (H3O+) or hydrogen (H+) ions

HA (g or l) –> H+ (aq) + A- (aq)

Can also be written involving formation of hydronium ion (H3O+)

HA (g or l) + H2O (l) –> H3O+ (aq) + A- (aq)

  • position of equilibrium lies to the right, means that strong acid completely dissociates into its constituent ions
  • solution of a strong acid contains virtually no undissociated HA molecules
  • conc. of H3O+ ions in solution = initial conc. of strong acid

NB/ for a strong acid, conc. of H+ ions = initial conc. of strong acid

44
Q

Organic acids

A
  • weak acids
  • when water is added, only a small % of its molecules dissociate to form H3O+ ions
  • an equilibrium is established, where majority of acid molecules don’t dissociate into ions
  • position of equilibrium lies to left
45
Q

Dissociation of a weak acid

A

HA (aq) H+(aq) + A-(aq)
Can also be written as:
HA(aq) +H2O (l) H3O+(aq) + A-(aq)

46
Q

Strong base

A

One which completely dissociates into ions in aqueous solution
- strong bases include metal hydroxides of group 1

General equation:
MOH(aq) –> M+(aq) + OH-(aq)

  • position of equilibrium for dissociation of a strong base lies to the right

Conc. of OH- ions = initial conc. of strong base

47
Q

Weak bases

A

All bases, except for hydroxides of group 1 and 2, are weak
- made up of molecules that react w/ water to release hydroxide ions

General equation for their dissociation:
B(aq) + H2O BH+(aq) + OH-(aq)

  • at equilibrium, most of the weak base molecules have not dissociated into ions
  • position of equilibrium lies to the left
48
Q

Weak acids and bases

A
  • for weak acids and bases, equilibrium conc. of H3O+ ions or OH- ions are much lower than for strong acids and bases
  • these differences in conc. can be used to distinguish between solution of weak and strong acids and bases
49
Q

Equimolar solutions

A

Solutions that have equal concentrations

  • Weak and strong acids and bases of the same concentration
  • distinguished due to their different properties eg. pH, electrical conductivity, and in case of acids, by their reactions w/ active metals
50
Q

Acids, bases and conductivity

A

Weak acids and bases have a lower conc. of mobile ions in solution- as they only partially ionise in solution
- hence, are a poor conductor of electricity

Strong acids and bases have a higher conc. of mobile ions in solution- completely ionise in solution
- good conductors of electricity

NB/ when comparing electrical conductivity of weak and strong acids and bases, solutions must be of equal conc.

51
Q

Acids, bases and reactivity

A

Bases do not react with metals

52
Q

Acids and conjugate bases

A

Strong acids - weak conjugate bases

  • a stronger acid will ionise more
  • position of equilibrium lies to the right
  • conjugate base is reactively weak

Weak acids- strong conjugate bases

  • conjugate base is relatively strong
  • equilibrium lies to the left
53
Q

Acid deposition

A

Refers to all types of acid precipitation

- can be classified as dry deposition eg. acidic gases and solid particles or wet deposition e.g. acid rain

54
Q

Acidity of rainwater

A

Natural rainwater is acidic- pH of 5.6

  • acidity is due to presence of carbon dioxide in the atmosphere
  • carbon dioxide reacts w/ water to form carbonic acid
55
Q

Acid rain

A
  • has pH of less than 5.0
  • formed when acidic gases eg. sulphur dioxide and oxides of nitrogen dissolve in water in atmosphere to produce sulphuric acid and nitric acid
56
Q

Formation of nitrogen monoxide

A
  1. During lightning storms by reaction of nitrogen and oxygen (2 predominant atmospheric gases)
  2. By reactions that take place in internal combustion engines
    - nitrogen reacts directly w/ oxygen at high temp. to produce nitrogen monoxide (a free radical- has an unpaired electron in valence shell of nitrogen atom)
    - takes place in both petrol and diesel engines; level of pollution is greater from diesel engines as operating temp. is higher
    - use of a catalytic converter in vehicle exhaust fumes reduces level of these emissions

Nitrogen oxide undergoes further oxidation in atmosphere to produce nitrogen dioxide (also a free radical)
- nitrogen dioxide reacts w/ water to form nitric and nitrous acid

57
Q

Sulphur dioxide

A
  • occurs naturally in the atmosphere as it’s released during volcanic eruptions
  • also produced when coal and oil that contain sulphur are burned in power stations
  • sulphur is a contaminating presence in coal and fuel oil used in power stations
  • sulphur (present in coal or fuel oil) is oxidised during combustion process and forms sulphur dioxide
58
Q

Photochemical oxidation

A
  • sulphur dioxide can also undergo photochemical oxidation in the atmosphere
  • process takes place in water droplets where sulphur dioxide is dissolved, catalysed by particulates eg. soot and fine metallic particles
  • reaction is complex, and isn’t a direct reaction w/ atmospheric oxygen
  • interactions w/ hydroxyl radicals, ozone or hydrogen peroxide are involved
  • sulphur dioxide and sulphur trioxide react w/ water in the atmosphere to form sulphurous and sulphuric acid
59
Q

Dry deposition

A
  • acidic particles and gases fall to ground via dust and smoke in absence of precipitation
  • this deposition can be washed into streams, lakes or rivers, causing harm to biological systems
60
Q

Environmental impact of acid deposition

A
  • can have serious consequences for living organisms eg. fish and trees
  • can enter aquatic ecosystems either directly eg. rain or indirectly as run-off
  • pH below 5.5, fish can’t survive, and prevents fish eggs from hatching
  • aluminium ions leached from soil by acid rain, enter rivers and streams and have harmful effects on fish gills
  • fish exposed to aluminium ions secrete excess mucous around gills, preventing oxygen uptake, leading to death by asphyxiation
  • loss of some species can cause knock-on effect through food chain- adversely affecting other organisms
  • biodiversity within a lake or river can be reduced by acid deposition as they become dominated by acid-tolerant species
61
Q

pH of soil

A
  • determines which species of plants grown in a certain location
  • aluminium is present in soil at high pH values as insoluble aluminium hydroxide
  • when pH falls, aluminium ions are released into soil where it can damage roots of plants, preventing uptake of water
  • acid deposition also has potential to leech essential plant nutrients from soil
62
Q

Acid deposition and effect on buildings

A

Statues and other architectural structures are often made from limestone or marble- both forms of calcium carbonate

  • calcium carbonate can react w/ sulphuric acid forming calcium sulphate, carbon dioxide and water
  • structures of iron, steel or aluminium can also be damaged by acid deposition
  • rate of rusting, being an electrolytic process, is increased by greater conc. of ions in acidic rainwater
63
Q

Acid deposition and effects on human health

A
  • acid rainwater and moisture in air can adversely affect mucous membranes and lungs
  • causes irritation and possibly exacerbating symptoms for people w/ asthma and other respiratory conditions
64
Q

Post-combustion methods

A

A method of reducing amount of acid deposition

- involves removing sulphur oxides from exhaust gases once they have been formed by reacting w/ a base

65
Q

Pre-combustion methods

A

A method of reducing amount of acid deposition

- involves removing sulphur before coal is combusted

66
Q

Hydrodesulphurisation

A

A pre-combustion method by which sulphur is removed from refined petroleum products eg. gasoline, jet fuel, kerosene and diesel fuel before combustion

  • takes place at high temp. and pressures in presence of a catalyst
  • sulphur is removed from product in form of hydrogen sulphide
67
Q

Flue gas desulphurisation

A
  • a post-combustion method used in power stations
  • levels of sulphur dioxide emissions in flue gases can be reduced by passing them into a flue gas desulphurisation tower
  • in this tower, gases are passed through a sprayed aqueous suspension of calcium carbonate and calcium oxide
  • product is calcium sulphite, which is further oxidised to produce calcium sulphate
68
Q

Rectification of acid deposition in soils and lakes

A

Soils and lakes whose pH has been significantly lowered by acid deposition can be treated w/ calcium hydroxide or limestone
- neutralises acidity and raises pH

69
Q

Redox reaction

A

A reaction that involves both oxidation and reduction

  • The two processes always take place together
  • if one reactant is oxidised during a reaction, another must be reduced
70
Q

Oxidation

A
  • gain of oxygen
  • loss of hydrogen
  • loss of electrons
  • results in an increase in oxidation state
71
Q

Reduction

A
  • loss of oxygen
  • gain of hydrogen
  • gain of electrons
  • results in a decrease in oxidation state
72
Q

Oxidising agent

A

A species that oxidises other species

  • readily accept electrons
  • reduced in the course of the reaction

NB/ an oxidising agent is reduced

73
Q

Reducing agent

A

A species that reduces other species

  • readily donate electrons
  • oxidised in the course of the reaction

NB/ a reducing agent is oxidised

74
Q

What are oxidation states?

A

Oxidation states that are assigned to atoms in a compound give a measure of control that an atom has over electrons in the compound

  • concept of oxidation states assumes that atoms lose or gain electrons according to their electronegativity values, regardless of whether they actually form ions or not
  • if an atom loses control over electrons- oxidised
  • if an atom gains control over electrons- reduced

Written with a sign (+/-) and a numerical value
+ = atom has lost electron control
- = atom has gained electron control

Numerical value= takes into account no. of electrons that atom has lost or gained control over

75
Q

Define oxidation state

A

A number which, together with its sign, indicates the gain or loss of electron control of an atom during a reaction

  • oxidation NUMBER is a numerical part of that value
  • it is used as a Roman numeral in the chemical formula of a compound
76
Q

Rules for determining oxidation states

A
  1. Free elements (O2, Cl2, N2) have oxidation state = 0
  2. Sum of oxidation states of all atoms in a compound = net charge on compound
  3. Alkali metals (Li, Na, K, Rb and Cs) in compounds = +1
  4. Fluorine in compounds is always -1
  5. Alkaline earth metals (Be, Mg, Ca, Sr, Ba and Ra) and Zn = +2
  6. Hydrogen in compounds = +1, except in certain metal hydrides = -1
  7. Oxygen in compounds = -2, except in peroxides = -1
  8. Halogens in compounds = -1
  9. Charge on a metal ion = same as its oxidation state
  10. Sum of oxidation states in a polyatomic ion must add up to charge on ion
77
Q

Exceptions to oxidation state

A

Some atoms can show variable oxidation states

- includes transition elements and non-metal elements

78
Q

Disproportionation

A

Occurs when same species is oxidised and reduced simultaneously during a reaction to form 2 different products
- eg. catalytic decomposition of hydrogen peroxide

79
Q

Lewis acid-base reactions

A

the transfer of an electron pair, with the subsequent formation of a coordinate bond

80
Q

Bronsted- Lowry theory of acids and bases

A

acids and bases are defined in terms of the transfer of protons (H+ ions)

81
Q

Lewis theory of acids

A

According to the Lewis theory, an acid is an electron pair acceptor and a base is an electron pair donor

82
Q

Lewis acid

A

an electron pair acceptor

- electrophiles

83
Q

Lewis base

A

an electron pair donor

- nucleophiles

84
Q

Bonding in complex ions according to Lewis theory

A

Complex ions are formed when a ligand uses a lone pair of electrons to form a coordinate covalent bond w/ a central metal ion
- in this complex ion, the ligands act as Lewis bases, and the central metal ion acts as a Lewis acid

85
Q

Dimer

A

a compound formed by the reaction of 2 similar monomers

IB Chemistry HL (9 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions