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chemistry > R3.1 - proton transfer reactions > Flashcards

R3.1 - proton transfer reactions Flashcards

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1
Q

What is a bronsted lowry acid?

A

A proton doner.

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2
Q

What is a bronsted lowry base?

A

A proton acceptor.

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3
Q

What is a proton?

A

In aqueous solution, it can be represented by H+ (aq) or H3O+ (aq).

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4
Q

What were some key discoveries about acids and bases?

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 acids.

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5
Q

What is the difference between a base and an alkali?

A

Base - substances which accept H+ ions.
Alkalis - substances that dissolve in water to form OH- ions.

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6
Q

What are conjugate pairs?

A

Acid and base pairs which differ by H+ (1 proton).

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7
Q

How do you work out the conjugate acid?

A

Add H+.

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8
Q

How do you work out the conjugate base?

A

Remove H+.

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9
Q

What is amphiprotic?

A

Substances that can act as both Bronsted Lowry acids and bases; have a double identity.

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10
Q

Why is water amphiprotic?

A

It can act as a proton acceptor and a proton donator.
- Must possess both a lone pair of electrons and H that can be released as H+.

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11
Q

What is the equation for water acting as an acid with NH3?

A

NH3 (B) + H2O (A) <–> NH4+ (CA) + OH- (CB)

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12
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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13
Q

What allows species to have a double identity?

A
  • To act as a Bronsted-Lowry acid, they must be able to dissociate and release H+.
  • To act as a Bronsted-Lowry base, they must be able to accept H+, which means they must have a lone pair of electrons.
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14
Q

What does amphoteric mean?

A

It can behave as an acid or base by reacting with the other substance.
E.g) Ammonium oxide in group 3.

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15
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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16
Q

Why can Al2O3 not be amphiprotic?

A

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

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17
Q

How does the acid and base in a conjugate pair differ?

A

Differs by H+.

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18
Q

What is acid rain?

A

Solution with a pH less than 5.6 that is formed when non-metal oxides react with water.
- Weak acids become stronger as they react.

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19
Q

What is the equation for sulfur dioxide and water?

A

1) SO2 (g) + H2O (l) <–> H2SO3 (aq)
2) H2SO3 (aq) <–> 2H+ (aq) + SO32- (aq)

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20
Q

What is the equation for nitrogen oxide and water?

A

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

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21
Q

What is the pH scale?

A

Logarithmic scale (uses powers of 10) used to measure the concentration of H+ ions.
- Power of Hydrogen scale.

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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 proportional to [H+].
  • For each increase of 10x in [H+], pH decreases by 1 unit.
  • At pH > 7, we still use [H+] to determine pH.
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25
Q

What happens to pH as [H+] ions increases?

A

As [H+] increases by 10x, the pH decreases by 1 unit.

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26
Q

How will pH decrease for each increase of 10x in [H+]?

A

pH will decrease by 1 unit.

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27
Q

What are the characteristics of pH < 7?

A
  • Acidic solutions
  • [H+] > [OH-]
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28
Q

What are the characteristics of pH > 7?

A
  • Alkaline solutions.
  • [OH-] > [H+]
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29
Q

What are the characteristics of pH = 7?

A
  • Neutral solutions.
  • [H+] = [OH-]
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30
Q

What is the ion product constant of water, Kw?

A

Kw = 1.0 x 10^-14
Kw = [H+] [OH-]
pH = 7 (water is neutral)

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31
Q

What is the process of ionization of water?

A

It is an endothermic process.
H2O (l) <–> H+ (aq) + OH- (aq)
K = ([OH-][H+]) / [H2O]
K[H2O] = Kw = [H+][OH-]
- [H2O] is a constant as the concentration of water is so large.

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32
Q

What is Kw dependent on?

A

Temperature:
Increase temperature = Kw shifts to the right, so Kw, [H+] and [OH-] increases, but pH falls.
Decrease temperature = Kw shifts to the left, so Kw, [H+] and [OH-] decreases, but pH increases.

33
Q

What type of reaction is the disassociation of water?

A

The dissociation of water into [H+] and [OH-] is endothermic.
- When temperature increases, the equilibrium shifts to the right, in favour of the forward reaction.

34
Q

How can we determine the type of solution using concentration?

A

Acidic: [OH-] < [H+]
Alkaline: [H+] < [OH-]
Neutral: [H+] = [OH-]

35
Q

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

A

1) Pure water = [OH-] [H+]
2) Kw = [OH-] [H+]
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) = pH 7

36
Q

What is the relationship between [H+] and [OH-]?

A

[OH-] and [H+] are inversely proportional in aqueous solutions.

37
Q

What does strength of an acid depend on?

A

Degree of ionisation

38
Q

What is strength?

A

The extent to which an acid or alkali ionizes.

39
Q

What is concentration?

A

The measure of the amount of [H+] ions.

40
Q

What is a strong acid?

A

An acid that completely dissociates in water.
- A strong acid has a weak conjugate base.

41
Q

What are some examples, with equations of strong acids?

A
  • HCl, HBr, HI, HNO3, H2SO4
    HCl (aq) + H2O (l) –> H3O+ (aq) + Cl- (aq)
42
Q

What is a weak acid?

A

An acid that partially dissociates in water.
- Weak acids have a strong conjugate base.

43
Q

What are some examples, with equations of weak acids?

A
  • CH3COOH, H2CO3, H3PO4, DNA
    CH3COOH (aq) + H2O (l) <–> H3O+ (aq) + CH3COO- (aq)
44
Q

What is a strong base?

A

A base that completely dissociates in water.
- Strong bases have weak acid conjugates.
- OH ions show Bronsted-Lowry base behaviour by accepting protons.

45
Q

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

A
  • NaOH, LiOH, KOH
    NaOH (aq) –> Na+ (aq) + OH- (aq)
46
Q

What is a weak base?

A

A base that partially dissociates in water.
- A weak base has a strong acid conjugate.
- There is a low concentration of ions and equilibrium lies to the left.

47
Q

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

A
  • NH3, C2H5, NH2
    NH3 (aq) + H2O (l) <–> NH4+ (aq) + OH- (aq)
48
Q

Where does acid-base equilibria lie?

A

Lies in the direction of the weaker conjugate.

49
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 acids make acidic conjugates.
OH- (aq) + H+ (aq) –> H2O (l)

50
Q

What is the most common substance?

A

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

51
Q

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

A

Increasing bond length and decreasing bond strength increases acid strength.

52
Q

What is the strongest acid?

A

HI - has the longest bond length and weakest bond strength.

53
Q

What is the weakest acid?

A

HF - has the shortest bond length and strongest bond strength.

54
Q

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

A

Conductivity increases with greater concentration of ions, and smaller size of ions.
- Strong acids and bases will shows a greater electrical conductivity.

55
Q

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

A

Strong acid = higher [H+] and lower pH
Weak acid = lower [H+] and higher pH
Strong base = higher pH
Weak base = lower pH

56
Q

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

A

Rates of reactions are faster with strong acids in comparison to weak acids.

57
Q

What is neutralisation?

A

Exothermic reaction in which an acid and base react to form a salt and water.

58
Q

What are alkalis?

A

Soluble bases that produce OH- ions when dissolved in water.

59
Q

What is the reaction between K2O and water?

A

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

60
Q

What are salts?

A

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

61
Q

What are reactions like with hydroxides and oxides?

A

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

62
Q

What is a spectator ion?

A

Ions that don’t change state or structure during the reaction, so can be cancelled out.
- Not included in the ionic or half-equation.

63
Q

What are reactions like with carbonates?

A

2HCl (aq) + CaCO3 (s) –> CaCl2 (aq) + h2O (l) + CO2 (g)
Ionic equation: 2H+ (aq) + CO3 2- (s) –> CO2 (g) + H2O (l)

64
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)

65
Q

What solutions are used to determine pH curves?

A

Strong acids and bases

66
Q

What is the point of inflection?

A

Point where there is a large jump in the pH of a solution.

67
Q

What is the point of equivalence?

A

Point where neutralization occurs.

68
Q

How can the pH curve be explained?

A

1) pH is initially low.
2) pH gradually changes.
3) Very large jump between pH 3 and 11.
4) Curve flattens out at high values.
5) Point of equivalence is pH 7.

69
Q

What is a monoprotic species?

A

When neutralization occurs with equal volumes of acids and bases.

70
Q

What is effervescence?

A

When a gas visibly produces bubbles when being released - usually refers to CO2.

71
Q

How do you carry out an investigation of the pH curve?

A

1) Add 23cm3 of NaOH to a conical flask using a pipette.
2) Add 50cm3 of HCl to a burette and let 1cm3 drop each time into the conical flask, gently stirring.
3) Record pH for every 1cm3 of HCl added 50 times using a pH probe and plot a graph.

72
Q

What is the pOH scale?

A

It describes the [OH-] ions in a solution.

73
Q

What are the equations involving the pOH scale?

A

pOH = -log(10) [OH-]
[OH-] = 10 ^-pOH
- Subtract from 14 if the solution is an alkali

74
Q

What are equations to show relationship between pOH and Kw?

A

pH + pOH = 14
pH + pOH = pKw

75
Q

What is the link between pKw and Kw?

A

As Kw gets larger, pKw decreases.
- Inversely proportional relationship

76
Q

What are equations to show the relationship between pKw and Kw?

A

pKw = -log(10) Kw
Kw = 10 ^-pKw

77
Q

How are pH and pOH derived?

A

They are derived from the concentrations of H+ and OH- at equilibrium.

78
Q

How are the strengths of weak acids and bases described?

A
79
Q

Why can we not determine the concentration of ions in a solution of a weak acid?

A

As the ions only partially ionise in water

chemistry (22 decks)

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