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SCH4U - Chem > 8.1 and 8.2 Strong/Weak Acids and Bases > Flashcards

8.1 and 8.2 Strong/Weak Acids and Bases Flashcards

1
Q

What is an acid according to the Arrhenius theory?

A

A substance that produces a hydrogen ion in an aqueous solution

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2
Q

What is a base according to the Arrhenius theory?

A

A substance that produces hydroxide ions in an aqueous solution

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3
Q

What is a hydrogen ion?

A

A hydrogen atom without an electron (basically a proton)

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4
Q

What makes HCl an acid according to Arrhenius?

A

It produces hydrogen ions when dissolving in water giving acidic properties

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5
Q

What makes NaOH a base according to Arrhenius?

A

It produces hydroxide ions when dissolving in water giving the solution basic properties

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6
Q

What are the problems with Arrhenius’s theory?

A
  • It assumes all acid base rxns occur in aqueous solutions
  • Only allows for 1 kind of base (containing OH-)
  • Later studies showed that basic solutions can be formed by compounds such as ammonia, that doesn’t contain OH-
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7
Q

What is the Bronsted Lowry theory?

A

That an acid is a hydrogen ion donor and a base is a hydrogen ion acceptor

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8
Q

What occurs when HF (g) dissolves in water according to Arrhenius and Bronsted-Lowry?

A

Arrhenius: That a hydrogen and fluoride ion will be produced
Bronsted-Lowry: HF reacts with water to form hydronium and fluoride ions

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9
Q

What is the acid and base in NH3 + H2O?

A

H2O is the acid because it donates a proton and NH3 is the base because it accepts one

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10
Q

What is a conjugate acid?

A

It is formed by a base accepting a hydrogen ion

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11
Q

What is a conjugate base?

A

An acid according to Bronsted Lowry donating a proton in the products

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12
Q

What is a conjugate acid base pair?

A

Two substances related together from donating and accepting a single hydrogen ion

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13
Q

What are the conjugate base pairs in:
Ex. HA (aq) + H2O (l) <-> A- (aq) + H3O+

A

1) Acid and conjugate base (HA and A-)
2) Base and conjugate acid (H2O and H3O+)

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14
Q

What makes the Bronsted-Lowry theory superior to the Arrhenius theory?

A
  • Arrhenius assumes acid base reactions only occur in aqueous solutions, but the Bronsted-Lowry theory extends to reactions in other states
  • Shows that you don’t need to have OH- to be a base, like NH3
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15
Q

What’s an Amphiprotic (amphoteric) substance?

A

A substance that can donate or accept hydrogen ions and thus acts like a Bronsted-Lowry acid and base (ex. water)

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16
Q

What is Ka?

A
  • The equilibrium constant for the ionization of an acid, also called the acid dissociation constant
  • When an acid reacts with water to form a conjugate base
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17
Q

What is hydronium replaced with in Ka?

A

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

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18
Q

What do bases and conjugate bases compete for?

A

Hydrogen ions

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19
Q

If Ka is large..

A

The acid has a higher affinity to H+, reaction shifts left

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20
Q

If Ka is small..

A

The H2O has a higher affinity to H+, reaction shifts right

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21
Q

What is a use of the Arrhenius theory?

A

Helps explain neutralization reactions:
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
H+(aq) + Cl-(aq) + Na+(aq) + OH-(aq) → Cl-(aq) + Na+(aq) + H2O(l)
H+(aq) + OH-(aq) → H2O(l)

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22
Q

What’s a problem with Arrhenius’s theory involving water?

A

He didn’t consider that acids/bases dissociated with water; he left water out of the reaction
Arrhenius: HCl (aq) → H+(aq) + Cl-(aq)
Water: HCl (aq) + H2O (l) → H+(aq) + Cl-(aq) + H2O (l)

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23
Q

Why is this incorrect?:
HCl (aq) + H2O (l) → H+(aq) + Cl-(aq) + H2O (l)

A

H+ do not exist in isolation in aqueous solutions, and water is POLAR, it interacts with ions, it cannot be unchanged

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24
Q

Protons are always…

A

Hydrated

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25
Q

What is a hydrated proton?

A

Water forming a dative covalent bond to a hydrogen ion to form hydronium

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26
Q

List all 6 strong acids.

A

HCl - hydrochloric acid
HBr - hydrobromic acid
HI - hydroiodic acid
H2SO4 - sulfuric acid
HNO3 - nitric acid
HClO4 - perchloric acid

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27
Q

What’s a monoprotic acid?

A

Only contains 1 hydrogen that can dissociate (HCl)

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28
Q

What’s a polyprotic acid?

A

Acid with more than one proton (H2SO4)

29
Q

Define a strong acid

A

It ionizes almost completely in water to produce hydrogen ions

30
Q

Define a weak acid

A

It only partially ionizes in water to produce hydrogen ions

31
Q

What happens to the original acid when dissolving and ionizing in water if it’s weak? If it’s strong?

A

Strong: Almost all acid molecules break apart to produce ions
Weak: Most of original acid is still in solution at equilibrium

32
Q

The stronger the acid…

A

The weaker its conjugate base

33
Q

What are the 3 properties of a strong acid?

A
  1. Large Ka
  2. Ionization equilibrium position shifted right
  3. [H+] ≈ [HA] at equilibrium
34
Q

What are the 3 properties of a weak acid?

A
  1. Small Ka
  2. Ionization equilibrium position shifted left
  3. [H+] < [HA] at equilibrium
35
Q

What’s an oxyacid?

A

An acid where the acidic hydrogen atom is attached to an oxygen atom (ex. Sulfuric acid (strong) and phosphoric acid (weak))

36
Q

What’s an organic acid?

A

An acid (not carbonic acid) that’s a carboxylic acid

37
Q

Are most organic acids weak or strong?

A

Weak, and its remaining hydrogen atoms are not acidic (don’t form H+ in water)

38
Q

In all acids, does the acidic hydrogen always bind to oxygen?

A

No, it can bind to a halogen

39
Q

What’s a strong base?

A

It dissociates completely in aqueous solution to form cations and hydroxide ions (shifts right)

40
Q

1.0mol/L of NaOH contains…

A

1.0mol/L of Na+ and 1.0mol/L of OH-

41
Q

What is the strength of group 1 and 2 hydroxide bases?

A

Strong

42
Q

What is the difference between a group 1 and group 2 hydroxide base

A

A group 2 base produces 2 mols of hydroxide ion for every 1 mol of metal hydroxide dissolved

43
Q

What is the solubility of an alkaline earth hydroxide? Why is that good?

A

Slightly soluble. It helps because antacids made of these bases prevent a release of high concentrated OH- ions that would harm the tissues lining the mouth and instead of dissolving in the mouth would dissolve in the acidic stomach solution.

44
Q

How does an antacid dissolve in an acidic stomach solution?

A

Dissolved OH- reacts with H+, and equilibrium shifts right and more base dissociates

45
Q

How does calcium hydroxide help the environment?

A

It scrubs SO2 from the exhaust of power plants because SO2 + atmospheric pressure becomes sulfurous acid, leading to acid precipitations. Ca(OH)2 combines with H2SO3 to make calcium sulfite and water which is less harmful to the environment

46
Q

Why is NH3 a base according to Bronsted-Lowry?

A

It reacts with water, accepting a hydrogen ion and producing OH and forms a dynamic equilibrium

47
Q

What’s an organic base?

A

An organic compound that increases concentration of hydroxide ions in aqueous solutions

48
Q

What’s an alkaloid?

A

An organic base derived from plants, fungi, and bacteria

49
Q

Are alkaloids weak or strong?

A

Weak, because they contain at least 1 nitrogen atom and an unbonded pair of electrons than can accept a hydrogen ion from water to leave behind a OH-

50
Q

What is the autoionization of water?

A

Transfer of a hydrogen atom from 1 water (amphiprotic) molecule to another to form hydronium and hydroxide

51
Q

What is Kb?

A

The equilibrium constant for the ionization of a base, also called the base dissociation constant

52
Q

What’s the ion product constant of water? (Kw)

A

The equilibrium constant for the autoionization of water (1 x 10^-14)

53
Q

In a neutral solution, [H] ? [OH]

A

=

54
Q

In a acidic solution, [H] ? [OH]

A

>

55
Q

In a basic solution, [H] ? [OH]

A

<

56
Q

What is the relationship between Kw, Ka, and Kb?

A
  • Ka multiplied by Kb = Kw
  • The equation of the ionization of a weak acid added to the equation of the ionization of the conjugate base gives the equation of the autoionization of water
57
Q

A strong acid/base..

A

Has a very weak conjugate

58
Q

A weak acid/base…

A

Has a weak conjugate

59
Q

A very weak acid/base…

A

Has a strong conjugate

60
Q

What is pH

A

The negative logarithm of the hydrogen ion concentration in aqueous solution

61
Q

What is pOH

A

The negative logarithm of concentration of hydroxide ions in aqueous solution

62
Q

How can we measure pH

A
  • Using a pH meter (not always practical)
  • Use a acid base indicator
63
Q

Name 2 acid base indicators

A

1 - Juice from red cabbages (turns red to brown)
2 - Litmus paper (turns red if acidic, blue if basic)

64
Q

How can you find [H+] from pH

A

10^-pH

65
Q

What is the effect of temperature on Kw

A

Kw increases with temperature

66
Q

If Kb&raquo_space; 1…

A

It’s a strong base

67
Q

How can you differentiate strong and weak acids experimentally?

A

1) pH measuring: Strong acids have lower pH
2) electrical conductivity: Strong acids conduct electricity better because they produce more ions
3) reaction rate: Strong acids react faster with metals or bases

68
Q

Why do weak acids establish equilibrium in water?

A

Because they only partially ionize, so forward and reverse reactions occur simultaneously until equilibrium is established

69
Q

Why is knowing conjugate acid base pairs important

A

Determines direction of equilibrium

SCH4U - Chem (9 decks)

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