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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
What is a hydrated proton?
Water forming a dative covalent bond to a hydrogen ion to form hydronium
26
List all 6 strong acids.
HCl - hydrochloric acid HBr - hydrobromic acid HI - hydroiodic acid H2SO4 - sulfuric acid HNO3 - nitric acid HClO4 - perchloric acid
27
What's a monoprotic acid?
Only contains 1 hydrogen that can dissociate (HCl)
28
What's a polyprotic acid?
Acid with more than one proton (H2SO4)
29
Define a strong acid
It ionizes almost completely in water to produce hydrogen ions
30
Define a weak acid
It only partially ionizes in water to produce hydrogen ions
31
What happens to the original acid when dissolving and ionizing in water if it's weak? If it's strong?
Strong: Almost all acid molecules break apart to produce ions Weak: Most of original acid is still in solution at equilibrium
32
The stronger the acid...
The weaker its conjugate base
33
What are the 3 properties of a strong acid?
1. Large Ka 2. Ionization equilibrium position shifted right 3. [H+] ≈ [HA] at equilibrium
34
What are the 3 properties of a weak acid?
1. Small Ka 2. Ionization equilibrium position shifted left 3. [H+] < [HA] at equilibrium
35
What's an oxyacid?
An acid where the acidic hydrogen atom is attached to an oxygen atom (ex. Sulfuric acid (strong) and phosphoric acid (weak))
36
What's an organic acid?
An acid (not carbonic acid) that's a carboxylic acid
37
Are most organic acids weak or strong?
Weak, and its remaining hydrogen atoms are not acidic (don't form H+ in water)
38
In all acids, does the acidic hydrogen always bind to oxygen?
No, it can bind to a halogen
39
What's a strong base?
It dissociates completely in aqueous solution to form cations and hydroxide ions (shifts right)
40
1.0mol/L of NaOH contains...
1.0mol/L of Na+ and 1.0mol/L of OH-
41
What is the strength of group 1 and 2 hydroxide bases?
Strong
42
What is the difference between a group 1 and group 2 hydroxide base
A group 2 base produces 2 mols of hydroxide ion for every 1 mol of metal hydroxide dissolved
43
What is the solubility of an alkaline earth hydroxide? Why is that good?
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
How does an antacid dissolve in an acidic stomach solution?
Dissolved OH- reacts with H+, and equilibrium shifts right and more base dissociates
45
How does calcium hydroxide help the environment?
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
Why is NH3 a base according to Bronsted-Lowry?
It reacts with water, accepting a hydrogen ion and producing OH and forms a dynamic equilibrium
47
What's an organic base?
An organic compound that increases concentration of hydroxide ions in aqueous solutions
48
What's an alkaloid?
An organic base derived from plants, fungi, and bacteria
49
Are alkaloids weak or strong?
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
What is the autoionization of water?
Transfer of a hydrogen atom from 1 water (amphiprotic) molecule to another to form hydronium and hydroxide
51
What is Kb?
The equilibrium constant for the ionization of a base, also called the base dissociation constant
52
What's the ion product constant of water? (Kw)
The equilibrium constant for the autoionization of water (1 x 10^-14)
53
In a neutral solution, [H] ? [OH]
=
54
In a acidic solution, [H] ? [OH]
>
55
In a basic solution, [H] ? [OH]
<
56
What is the relationship between Kw, Ka, and Kb?
- 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
A strong acid/base..
Has a very weak conjugate
58
A weak acid/base...
Has a weak conjugate
59
A very weak acid/base...
Has a strong conjugate
60
What is pH
The negative logarithm of the hydrogen ion concentration in aqueous solution
61
What is pOH
The negative logarithm of concentration of hydroxide ions in aqueous solution
62
How can we measure pH
- Using a pH meter (not always practical) - Use a acid base indicator
63
Name 2 acid base indicators
1 - Juice from red cabbages (turns red to brown) 2 - Litmus paper (turns red if acidic, blue if basic)
64
How can you find [H+] from pH
10^-pH
65
What is the effect of temperature on Kw
Kw increases with temperature
66
If Kb >> 1...
It's a strong base
67
How can you differentiate strong and weak acids experimentally?
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
Why do weak acids establish equilibrium in water?
Because they only partially ionize, so forward and reverse reactions occur simultaneously until equilibrium is established
69
Why is knowing conjugate acid base pairs important
Determines direction of equilibrium

SCH4U - Chem (9 decks)

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