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reactivity 3 Flashcards

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1
Q

What is a bronsted lowry acid?

A

proton doner

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2
Q

What is a bronsted lowry base?

A

proton acceptor

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3
Q

How can this be shown with HCl and HC3?

A

HCl + NH3 ⇌

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4
Q

What is a proton?

A

in aqueous solutions, it can be represented as H+ (aq) or H3O + (aq)

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5
Q

What were some key discoveries?

A

1887 - arhenius said that acids form H+ ions and alkalis form OH- ions
1823 - bronsted lowry said that acids and bases donate and accept electrons

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6
Q

How do you work out the conjugate acid?

A

add H+

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7
Q

What is amphiprotic?

A

ability to both accept and donate electrons e.g) water

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8
Q

What allows species to have a double identity?

A

BL acid - disasociates and release H+
BL base - accepts H+ - must have a lone pair of electrons

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9
Q

What is the difference between a base and an alkali?

A

base - substances which accept H+ ions
alkali - bases that dissolve in water to form OH- ions

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10
Q

What are conjugate pairs?

A

a pair of species differing by H+ (a single proton)
- acids and bases cannot react in isolation

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11
Q

How do you work out the conjugate base?

A

remove H+

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12
Q

Why is water ampiphrotic?

A

it acts as an acid with ammonia and a base with ethanoic acid
- HCO3 - is also ampiphrotic

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13
Q

What does amphoteric mean?

A

can behave as an acid or base by reacting with acids or bases such as ammonium oxide in group 3

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14
Q

What is the equation for water acting as an acid with ammonia?

A

NH3(B) + H2O(A) ⇌ NH4+(CA) + OH-(CB)

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15
Q

What is the equation for water acting as a base with ethanoic acid?

A

CH3COOH(B) + H2O(A) ⇌ CH3COO-(CA) + H3O+(CB)

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16
Q

What are the equations for Al2O3?

A

Al2O3 (s) + 3H2SO4 (aq) –> Al2(SO4)3 (aq) + 3H2O (l)
Al2O3 (s) + 3H2O (l) + 2OH- (aq) –> 2Al(OH)4- (aq)

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17
Q

Why can it not be amphiprotic?

A

it has no proton (H+) to donate and reacts with acids to form salt and water

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18
Q

What is acid rain?

A

non-metal oxides react with water to form a solution with pH less than 5.6 (weak acids become stronger as they react)

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19
Q

What is the equation for sulfur dioxide?

A

SO2 (g) + H2O (l) ⇌ H2S03 (aq)
H2S03 (aq) ⇌ 2H+ (aq) + SO32- (aq)

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20
Q

What is the equation for nitrogen oxide?

A

2NO2 (g) + H2O (l) –> HNO2 (aq) + HNO3 (aq)

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21
Q

What is the pH scale?

A

power of hydrogen scale used to measure the concentration of H+ ions
- logarithmic scale which uses powers of 10

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22
Q

What are the key equations?

A

pH = -log [ H+]
[ H+] = 10 ^-pH

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23
Q

How can we measure pH?

A

using a pH probe or universal indicator

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24
Q

What are the key properties of pH?

A
  • pH doesn’t have any units
  • pH is inversely related to [ H+]
  • for each increase of 10x in [ H+], pH decreases by 1 unit
  • at pH greater than 7, we still use [ H+] to determine pH
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25
Q

What is the ion product constant of water, Kw?

A

Kw = 1.0 x 10-14
Kw = [ H+][ OH-]

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26
Q

What is the process of ionization of water?

A

endothermic process
H2O (l) ⇌ H+ (aq) + OH- (aq)
K = ([ H+][ OH-]) / [ H2O]
K[ H2O] = [ H+][ OH-] = Kw
[ H2O] is constant as concentration of water is so large

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27
Q

What is Kw dependent on?

A

increase temperature - shifts to the right so Kw [ H+] [ OH-] increases and pH falls
decrease temperature - shifts to the left so Kw [ H+] [ OH-] decreases and pH increases

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28
Q

How can we determine the type of solution using concentration?

A

acidic solution - pH is smaller than 7
- [ H+] >[ OH-]
alkaline solution - pH is greater than 7
- [ H+] <[ OH-]
neutral solution - pH is 7
- [ H+]= [ OH-]

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29
Q

How can we work out Kw and pH of pure water?

A
  1. pure water, [ H+] [ OH-]
  2. Kw = [ H+] [ OH-]
  3. Kw = [ H+] 2
  4. [ H+] 2 = 1.0 x 10-14
  5. [ H+] = 1.0 x 10-7
  6. pH = -log(1.0 x 10-7) = 7 so the pH of pure water is 7 (neutral)
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30
Q

What does strength of an acid depend on?

A

degree of ionisation

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31
Q

What is the relationship between bond length, bond strength and acid strength?

A

as bond length increases, bond strength decreases and acid strength increases

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32
Q

What is strength?

A

how much an acid or alkali ionizes

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33
Q

What is a strong acid? What are some examples, with equations?

A

an acid that completely dissociates in water
- HCl, HBr, HI, HNO3, H2SO4
HCl (aq) + H2O (l) –> H3O+ (aq) + Cl- (aq)
- strong acid has a weak conjugate base (lower in pH)

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34
Q

Where does acid-base equilibria lie?

A

lies in the direction of the weaker conjugate

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35
Q

What is a weak acid? What are some examples, with equations?

A

when acids partially ionize water
- CH3COOH, H2CO3, H3PO4, DNA
CH3COOH (aq) + H2O (l) ⇌ H3O+ (aq) + CH3COO- (aq)
- weak acid has a strong conjugate base

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36
Q

What is the most common substance?

A

weak acids - any molecule with a carboxyl group (COOH)

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37
Q

What is the weakest acid?

A

HF - has the shortest bond length and strongest bond strength

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38
Q

What is concentration?

A

the measure of the concentration of H+ ions

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39
Q

What is the strongest acid?

A

HI - has the longest bond length and weakest bond strength

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40
Q

What is a strong base? What are some examples, with equations?

A

base that completely disasociates in water e.g) NaOH, LiOH, KOH
NaOH (aq) –> Na+ (aq) + OH- (aq)
- OH ions show bronsted lowry base behaviour by accepting protons

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41
Q

What base is a better proton acceptor and why?

A

strong bases are better proton acceptors as they readily accept protons to form conjugates with non-acidic properties whereas weak bases make acidic conjugates
OH- (aq) + H+ (aq) –> H2O (l)

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42
Q

What is a weak base? What are some examples, with equations?

A

a base that partially ionizes in water e.g)NH3, C2H5, NH2
NH3 (aq) + H2O (l) ⇌ NH4+ (aq) + OH- (aq)
- there is a low concentration of ions and equilibrium lies to the left

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43
Q

How are strong and weak acids and bases different in terms of electrical conductivity?

A

conductivity increases with greater concentration of ions and with smaller ions

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44
Q

How are strong and weak acids and bases different in terms of rate of reaction?

A

if you reacted magnesium with identical concentrations of a strong and weak acid, Mg would react rapidly with the strong acid but barely with the weak acid due to the concentration of H+ ions

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45
Q

How are strong and weak acids and bases different in terms of pH?

A

strong acid - higher H+ concentration - lower pH
weak acid - lower H+ concentration - higher pH

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46
Q

What is neutralisation?

A

exothermic reaction when an acid and base react to form a salt and water

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47
Q

What are alkalis?

A

soluble bases that produce OH- ions when dissolved in water

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48
Q

What is the reaction between K2O and water?

A

K2O (s) + H2O (l) –> 2K+ (aq) + 2OH- (aq)

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49
Q

What are salts?

A

ionic compounds where the H in an acid is replaced by a metal or other positive ions

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50
Q

What are reactions like with hydroxides and oxides?

A

HNO3 (aq) + NH4OH (aq) –> NH4NO3 (aq) + H2O (l)
- NO3+ and NH4- are the spectator ions
ionic equation = H+ + OH- –> H2O

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51
Q

What is a spectator ion?

A

ion that doesn’t change state during the reaction so can be cancelled out

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52
Q

What are reactions like with carbonates?

A

2HCl (aq) + CaCO3 (s) –> CaCl2 (aq) + H2O (l) + CO2 (g)
ionic equation = 2H+ (aq) + CO32- (s) –> CO2 (g) + H2O (l)

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53
Q

What is effervescence?

A

when a gas visibly produces bubbles when being released

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54
Q

What are reactions like with metals?

A

Mg (s) + 2HCl (aq) –> MgCl2 (aq) + H2 (g)
oxidation = Mg (s) –> Mg2+ (aq) + 2e-
reduction = 2H+ (aq) + 2e- –> H2 (g)

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55
Q

What is oxidation in terms of oxygen, hydrogen, electrons and oxidation states?

A
  • gain in oxygen
  • loss of hydrogen
  • loss of electrons
  • increase in oxidation state
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56
Q

What is reduction in terms of oxygen, hydrogen, electrons and oxidation states?

A
  • loss of oxygen
  • gain in hydrogen
  • gain of electrons
  • decrease in oxidation state
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57
Q

What are limitations of the oxidation states model?

A

it is difficult to assign integer oxidation states to compounds with more than one atom of an element e.g) C3H8

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58
Q

What is the oxidation state of carbon in C3H8?

A

-2.66

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59
Q

What is an oxidizing agent?

A

when the species accepts electrons (reduction)

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60
Q

What are some examples of oxidizing agents?

A

O2, ozone, MnO4-, Cr2O72-, OH-, H2O2, HNO3, H+

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61
Q

What are some examples of reducing agents?

A

H2, C, CO, SO2, reactive metals

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62
Q

What is a reducing agent?

A

when the species donates electrons (oxidation)

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63
Q

What can act as both reducing and oxidizing agents?

A

H2O and hydrogen peroxide (H2O2)

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64
Q

What solutions are used to determine pH curves?

A

strong acids and bases

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65
Q

How can the pH curve be described?

A
  1. pH is initally low
  2. pH gradually changes
  3. very large jump in pH between 3 and 11
  4. curve flattens out at high values
  5. point of equivalence is at pH 7
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66
Q

What is the point of inflection?

A

point where there is a large jump in the pH of the solution

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67
Q

What is the point of equivalence?

A

point where neutralization occurs

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68
Q

What is a monoprotic reaction?

A

when neutralization occurs with equal volumes of acids and bases

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69
Q

How can you carry out an investigation of a pH curve?

A
  1. add 25cm3 of sodium hydroxide to a conical flask using a pipette
  2. add 50cm3 of hydrochloric acid to a burette and let 1cm3 drop each time into the conical flask, gently stirring
  3. record the pH every 1cm3 for 50 times using a pH probe and plot a graph
70
Q

What are limitations of oxidation states?

A

it can be difficult to assign integer oxidation states to compounds with more than 1 atom of an element such as C3H8

71
Q

What is an oxidizing agent? What are some examples?

A

if the species accepts electrons - reduction
- oxygen, ozone, MnO4-, Cr2O7 2-, OH-, H2O2, HNO3, H+

72
Q

What is a reducing agent? What are some examples?

A

if the species donates electrons - oxidation
- H2, C, CO, SO2, reactive metals

73
Q

What are some exceptions?

A

H2O and H2O2 can be both oxidizing and reducing agents

74
Q

What do half equations show?

A

shows the electron transfer process in redox reactions

75
Q

How do you write a full, balanced equation using oxidation states?

A
  1. write the unbalanced equation and assign oxidation states
  2. write the half equations
  3. balance O by adding H2O to the opposite side of the equation
  4. balance H by adding H+ ions to the opposite side of the equation
  5. balance the number of electrons and check if the charge number balances
  6. add the 2 half equations and cancel out if anything is similar
76
Q

What is a redox titration?

A

used to determine concentrations in redox reactions

77
Q

What is the equation for the iodine-thiosulfate titration?

A

2I- (aq) + oxidising agent (clear) –> I2 + other products (blue)
2S2O3 2- (aq) + I2 (aq) –> 2I- (aq) + S4O6 2- (aq)

78
Q

What are the half equations for the iodine-thiosulfate titration?

A

oxidation = 2S2O3 2- –> S4O6 2- + 2e-
reduction = I2 + 2e- –> 2I-

79
Q

How does the iodine-thiosulfate reaction work?

A
  • iodine ions are oxidised to iodide and titrated against sodium thiosulfate which reduces iodide back to iodine, using starch as an indicator
  • the starch forms a deep blue colour with iodine molecules in the complex
  • as the I2 is reduced to I-, the blue colour disappears
  • starch is added at intervals during the titration
80
Q

What is the equation for the titration with iron and manganese?

A

5Fe 2+ (aq) + MnO4- (aq) + 8H+ (aq) –> 5Fe 3+ (aq) + Mn2+ (aq) + 4H2O(l)

81
Q

What are the half equations for the titration with iron and manganese?

A

oxidation = Fe3+ –> Fe2+ + e-
reduction = MnO4- + 8H+ + 5e- –> Mn2+ + 4H2O

82
Q

What happens during the titration of iron and manganese?

A

KMnO4 is used in acidic conditions to oxidise Fe2+ to Fe3+ and reduce MnO4- to Mn2+
- colour changes from deep purple to colourless
- reaction mixture acts as it’s own indicator

83
Q

What is the order of the reactivity series?

A

K, Na, Ca, Mg, Al, C, Zn, Fe, Sn, Pb, Cu, Ag, Au

84
Q

Which non-metals are stronger oxidising agents?

A

more reactive non-metals

85
Q

Which metals are stronger reducing agents?

A

more reactive metals

86
Q

What happens when an acid reacts with a metal?

A

salt and hydrogen

87
Q

Why is H important in the reactivity series?

A

anything less reactive than H will not react with acids

88
Q

What are electrochemical cells made out of?

A

voltaic cells and electrolyctic cells

89
Q

What are voltaic cells?

A

cells that generate electricity from chemical reactions

90
Q

What are electrolyctic cells?

A

cells that use electricity to drive chemical reactions

91
Q

What is a primary voltaic cell?

A

electrochemical cell that converts energy from spontaneous redox reactions to electrical energy (single use e.g) lithium batteries in remotes)

92
Q

How is the type of reaction different for voltaic and electrolyctic cells?

A

voltaic - spontanteous
electrolyctic - non spontaneous

93
Q

How do the electrons flow?

A

from anode (most reactive) to cathode (least reactive)

94
Q

What is the polarity of the anode and cathode at the voltaic cell?

A

anode - negative
cathode - positive

95
Q

Where does oxidation and reduction occur for voltaic and electrolyctic cells?

A

oxidation - anode (vowels)
reduction - cathode (consonants)

96
Q

What is the polarity of the anode and cathode at the electrolyctic cell?

A

anode - positive
cathode - negative

97
Q

What happens when a copper half cell and zinc half cell are connected by a wire?

A

nothing until the circuit is fully complete

98
Q

What is the purpose of a salt bridge?

A

connects and completes the circuit so that ions can flow to neutralise the build up of positive and negative charges

99
Q

What are the 5 rules for drawing a cell diagram?

A
  1. vertical lines represent state boundary
  2. double vertical lines represent the salt bridge
  3. aqueous solutions are placed next to the salt bridge
  4. anode on the left and cathode on the right
  5. electrons flow from left to right
100
Q

What can be used as a salt bridge?

A

glass or filter paper with NaCl

101
Q

What do the negative ions in the salt bridge do?

A

negative ions neutralize the metal ions at the anode to force equilibrium to the right so that more electrons are made to generate more electricity and keep the reaction going

102
Q

What do the positive ions in the salt bridge do?

A

positive ions neutralize the negative ions in the salt solution to free the metal so that it can bind to the electrons

103
Q

What is present at the anode and what are the observations?

A

most reactive metal
- oxidation occurs
- anode loses mass

104
Q

What is present at the cathode and what are the observations?

A

least reactive metal
- reduction occurs
- cathode gains mass

105
Q

How can a primary voltaic cell lose it’s battery?

A
  • anode is used up so is no longer submerged in the solution
  • solution at the cathode is used up so that cathode cannot reach the solution
106
Q

How do anions migrate through the salt bridge?

A

cathode to anode

107
Q

How do cations migrate through the salt bridge?

A

anode to cathode

108
Q

How can half-cells produce electric potentials?

A

the half cell has a metal and a solution of the metal ( copper and copper sulfate)
- Cu loses electrons to form Cu2+ and the electrons stick to the outside of the Cu atoms and the Cu2+ is attracted to the e-
Cu ⇌ Cu2+ + 2e-

109
Q

What is a secondary cell?

A

a cell that can be reversed or recharged when an external current is applied

110
Q

Why are lithium-ion batteries useful?

A
  • low density
  • high reactivity
  • stores a lot of electrical energy per unit mass
111
Q

When can the system be reversed?

A

if one of the products in insoluble as the product cannot disperse away from the electrode

112
Q

What electrolyte is used in a lithium-ion battery?

A

non-aqueous polymer based electrolyte

113
Q

What problems are there with the lithium-ion battery?

A
  • due to it’s high reactivity, it forms lithium oxide which prevents it into coming into contact with the electrolyte, reducing the effectiveness
114
Q

How can the problems in a lithium-ion battery be resolved?

A
  • lithium anode is mixed with graphite
  • lithium cathode is placed in a lattice with a metal oxide (MnO2)
115
Q

What are the half-equations for discharging in a lithium-ion battery?

A

anode (-) = oxidation = Li –> Li+ + e-
cathode (+) - reduction = Li + MnO2 + e- –> LiMnO2

116
Q

What are the half-equations for recharging in a lithium-ion battery?

A

anode (-) = reduction = Li+ + e- –> Li
cathode (+) = oxidation = LiMnO2 –> MnO2 + e- + Li+

117
Q

What happens at the anode and cathode in discharging?

A

anode (-) = oxidation
cathode (+) = reduction

118
Q

What happens at the anode and cathode in recharging?

A

anode (-) = reduction
cathode (+) = oxidation

119
Q

Why are hydrogen fuel cells useful?

A
  • reduces dependence on fossil fuels
  • produces a lot of heat energy when combined with oxygen (286kJ)
120
Q

What are the equations for a hydrogen fuel cell in an acidified environment?

A

overall = H2 + 0.5O2 –> H2O
anode (-) = oxidation = 2H2 –> 4H+ + 4e-
cathode (+) = reduction = 4H+ + 4e- + O2 –> 2H2O

121
Q

What are the equations for a hydrogen fuel cell in an alkaline environment?

A

overall = H2 + 0.5O2 –> H2O
anode (-) = oxidation = H2 + 2OH- –> 2H2O + 2e-
cathode (+) = reduction = 2H2O + O2 + 4e- –> 4OH-

122
Q

What are the pros and cons of general primary cells?

A

pros - inexpensive and light
cons - lots of waste, single use, small current

123
Q

What are the pros and cons of primary fuel cells?

A

pros - efficient, no pollution, low density
cons - expensive, explosive, small current

124
Q

What are the pros of general secondary cells?

A

pros - high current and material can be regenerated

125
Q

What are the pros and cons of a lead-acid secondary cell?

A

pros - lots of energy
cons - heavy and pollution

126
Q

What are the pros and cons of a cadmium-nickel secondary cell?

A

pros - longer life span
cons - toxic and expensive

127
Q

What are the pros and cons of a lithium ion secondary cell?

A

pros - high voltage, low density
cons - expensive and limited supply

128
Q

what are electrolytic cells?

A

opposite to voltaic cells
- use an external power source to bring about a redox reaction which is non spontaneous

129
Q

what occurs at the anode and cathode of electrolytic cells?

A

anode - oxidation - negative non-metals are attracted here
cathode - reduction - positive metals are attracted here

130
Q

what is the polarity of an anode and cathode in an electrolytic cell?

A

anode - positive
cathode - negative

131
Q

what are the general half equations at the anode and cathode?

A

anode = A- –> A + e-
cathode = M+ + e- –> M

132
Q

how is electrolysis done on an industrial scale?

A

to save money, the salt that will be electrolysed is dissolved in another molten salt solution to lower the melting point of the mixture
- cryolite –> aluminum oxide
- CaCl2 –> NaCl

133
Q

what is a radical?

A

chemical entities that have unpaired electrons and are highly reactive and have a high enthalpy

134
Q

why are radicals highly reactive?

A

it is energetically favourable for them to take an electron from other species or to combine with other radicals to form a covalent bond

135
Q

what are some examples of common atomic radicals?

A

Chlorine, Bromine, Hydrogen

136
Q

what are some common examples of molecular radicals?

A

Nitric oxides, Hydroxyl, Methyl

137
Q

what are neutral radical and why?

A

Molecular and Atomic radicals
- same number of protons and electrons

138
Q

what are anionic radicals?

A

Molecules that can gain electrons to become radicals
- O2- or C6H6-

139
Q

what are cationic radicals?

A

molecules that can lose electrons to become radicals
- M+ or C2H5OH+

140
Q

why are anionic and cationic radicals not neutral?

A

not equal number of protons and electrons

141
Q

how are radicals made?

A

homolytic fission - covalent bond breaks to form 2 radicals with equal assignment of electrons
- in the presence of heat or high energy UV

142
Q

what are CFC’s?

A

Chlorofluorocadbons which were used in aerosols, solvents and plastics and break down to release a chlorine radical which acts as a catalyst for the decomposition of O3

143
Q

why do CFC’s break down to release a chlorine radical but not a fluorine radical?

A

chlorine has weaker bonds compared to fluorine when UV radiation is absorbed so is easier to break the bonds

144
Q

What is an example of a common oxidising agent?

A

acidified potassium dichromate (K2Cr2O7)

145
Q

What colour is K2Cr2O7?

A

bright orange which turns dark green if reduced to Cr3+ when alcohol is oxidised

146
Q

What is a reflux reaction?

A

a reaction with constant cycling of boiling, condensing and evaporating

147
Q

What happens during the oxidation of primary alcohols?

A

primary alcohol –> aldehyde –> carboxylic acid

148
Q

what happens when ethanol undergoes oxidation?

A
  • ethanol loses H to make ethanal
  • ethanal gained O to make ethanoic acid
149
Q

how can ethanal be obtained?

A

using distillation

150
Q

what happens during the oxidation of a secondary alcohol?

A

secondary alcohol –> ketone

151
Q

what happens during the oxidation of a tertiary alcohol?

A

tertiary alcohol –> no reaction

152
Q

what are the colour changes for primary, secondary and tertiary alcohols?

A

primary = orange –> green
secondary = orange –> green
tertiary = orange –> green

153
Q

why are alkanes so unreactive?

A

contains strong C-C and C-H bonds which take a lot of energy to break and are non-polar so don’t attract reactive species such as electrophiles and nucleophiles

154
Q

what is the activation energy for alkanes?

A

large activation energy so are unreactive and kinetically stable

155
Q

what is the enthalpy change for alkanes?

A

negative enthalpy change are are thermodynamically unstable compared to their products

156
Q

what are the 3 stages of a radical substitution reaction?

A

initiation - making the radical
propagation - making new radicals
termination - removing the radicals

157
Q

what occurs doing the initiation stage?

A
  • 1 step reaction
  • requires high energy UV light to be present
  • a molecule splits into 2 new radicals - molecule with the weakest bond is broken
    E=hf –> energy corresponds to the frequency of UV needed to break bonds
158
Q

what occurs doing the propagation stage?

A
  • 2 step reaction (chain reaction)
  • radicals formed in initiation react and a radical is reformed
159
Q

what occurs during the termination stage?

A
  • includes 3 steps
  • 2 radicals combine to make 1 non-radical product
160
Q

what happens if alkanes react with bromine water?

A

alkanes are saturated hydrocarbons that undergo substitution reactions
UV = bromine water is decolourised as a photochemical reaction occurs
Dark = no reaction and no colour change

161
Q

What is the reagent and conditions for reduction reactions?

A
  • LiAlH4 (contains H- ions)
  • heated in dry ether
162
Q

What happens in the reduction of a ketone and carboxylic acid?

A

ketone –> secondary alcohol
carboxylic acid –> aldehyde –> primary alcohol

163
Q

What does reduction of unsaturated compounds do?

A

lowers the degree of unsaturation

164
Q

What are examples of unsaturated hydrocarbons?

A
  • alkenes
  • alkynes
165
Q

What does saturated mean?

A

an atom where molecules are linked by single bonds

166
Q

What does unsaturated mean?

A

an atom where the molecules have a single double bond

167
Q

What reactions can unsaturated compounds undergo?

A
  • hydrogenation
  • reduction
  • addition
168
Q

What happens if propene is reduced?

A

propene –> propane

169
Q

What is hydrogenation?

A

adding of hydrogen

170
Q

What is an example of hydrogenation?

A

liquid oil –> solid fat
oil –> margerine

171
Q

What is the relationship between saturation and melting point?

A

more saturation = straighter chains = higher melting points = solid

172
Q
A

chemistry (28 decks)

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