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Chemistry > Topic 8: Acids and Bases > Flashcards

Topic 8: Acids and Bases Flashcards

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1
Q

Bronsted-Lowry acid

A

A substance that behaves as an acid when it donates a proton.

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2
Q

Bronsted-Lowry base

A

A substance that behaves as a base when it accepts a proton.

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3
Q

Conjugate acid-base pair definiton

A

A pair of species differing by a single proton

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4
Q

An acid becomes into …

A

conjugate base

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5
Q

A base becomes into a …

A

conjugate acid

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6
Q

Amphiprotic definition

A

Substance capable of accepting and donating H+, thus able to act as a Bronsted-Lowry acid and base

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7
Q

Example of amphiprotic substance

A

H2O (H3O+ / OH-)

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8
Q

Amphoteric definiton

A

A species that can act as an acid or base, including reactions that do not involve H+ transfer

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9
Q

Relationship between amphoteric and amphiprotic reactions

A

All amphiprotic species are also amphoteric but not all amphoteric species are amphiprotic.

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10
Q

Equation of reaction of an acid with a metal

A

Metal + Acid => Salt + H2(g)
Example: Zn(s) + 2HCl(aq) => ZnCl2(aq) + H2(g)

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11
Q

Which type of metals do acids react with?

A
  • Reactive metals (e.g., Ca / Mg / K / Zn)
  • No unreactive metals (e.g., Cu / Au / Ag)
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12
Q

Neutralization reaction

A

Chemical reaction where a base and an acid react to form a salt and water

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13
Q

Why are neutralization reactions exothermic?

A
  • When a strong acid and a strong base are dissolved in water, they are completely dissociated into their ions.
  • The anions from the acid and the cations from the base remain in solution as spectator ions.
  • The only reaction that takes place is the reaction between hydronium and hydroxide ions to form water, and this reaction is exothermic.
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14
Q

Equation of reaction of an acid with metal oxides and metal hydroxides

A

Acid + Base => Salt + Water
Example: HCl(aq) + NaOH(aq) => NaCl(aq) + H2O(l)

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15
Q

Equation of reaction of an acid with carbonate and hydrogen carbonate

A

Acid + Carbonate => Salt + H2O(l) + CO2(g)
Example: Na2CO3(aq) + H2SO4(aq) => Na2SO4(aq) + H2O(l) + CO2(g)

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16
Q

Indicator definition

A
  • Substances that have different color according to the concentration of H+ ions in the solution
  • Weak acids whose conjugates have different colors
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17
Q

Common indicators (Acid => Base)

A

Methyl orange (Red => Yellow)
Litmus (Pink => Blue)
Phenolphthalein (Colorless => Pink)

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18
Q

Why does water self-ionize?

A

Due to its amphoteric nature

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19
Q

Chemical equation of ionization of water

A

2H2O(l) ⇌ H3O+(aq) + OH-(aq)

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20
Q

Ionization constant of water (Kw)

A

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

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21
Q

Based on the relative concentrations of H+ and OH-, a solution is:
a) Neutral if…
b) Acidic if…
c) Basic if…

A

a) [H+] = [OH-]
b) [H+] > [OH-]
c) [H+] < [OH-]

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22
Q

Formulas for calculating pH and pOH from their concentrations

A
  • pH = -log[H+]
  • pOH = -log[OH-]
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23
Q

Formula for calculating pKw at 298 K

A

pKw = pH + pOH = 14.00

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24
Q

Acidity of a solution when pH is:

a) = 7.00
b) < 7.00
c) > 7.00

A

a) Neutral
b) Acidic
c) Basic

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25
Q

1 unit change in pH equals … in the H+ ion concentration

A

tenfold change

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26
Q

Methods to measure pH

A
  • Universal indicator
  • pH meter
27
Q

Functioning of universal indicator

A

The substance tested gives a distinct color, which is compared with a color chart supplied with the indicator

28
Q

Functioning of pH meter

A

The probe directly reads the [H+} concentration through a special electrode

29
Q

What is the main difference between strong and weak acids/bases?

A

Extent of ionization/dissociation
- Strong fully dissociate in solution (=>)
- Weak partially dissociate in solution (<=>)

30
Q

Which type of substance produces more OH-/H+ ions at the same concentration?

A

Strong acids/bases

31
Q

7 strong acids

A
  • HCL
  • HNO3
  • H2SO4
  • HBr
  • HI
  • HClO4
  • HClO3
32
Q

Examples of weak acids

A
  • CH3COOH
  • H2CO3
  • C₃H₆O₂
  • H3PO4
33
Q

Examples of strong bases

A
  • Group 1 Hydroxides
  • Ba(OH)2
34
Q

Examples of weak bases (2)

A
  • NH3 (Ammonia)
  • C2H5NH2
35
Q

Definition of a strong acid

A

It is a good proton donor and has a weak conjugate base

36
Q

Definition of a strong base

A

It is a good proton acceptor and has a weak conjugate base

37
Q

Experimental techniques used to determine acid / base strengths

A

a) Conductivity
b) pH
c) Rates of reaction

38
Q

Hypothesis using conductivity to determine strength of an acid / base

A

Strong acids and bases will be better conductors than weak acids and bases at the same concentration

39
Q

Explanation of difference in conductivity between strong and weak acids/bases

A
  • The concentration of H+ will be higher in a strong acid than in a weak acid, and the concentration of OH- will be higher than in a weak base
  • The more ions present, the more conductive a solution.
40
Q

Hypothesis using pH to determine strength of an acid / base

A

At the same concentration, strong acids have lower pH than weak acids / strong bases have a higher pH than weak bases

41
Q

Explanation of difference in pH between strong and weak acids/bases

A
  • Because pH is a measure of H+ concentration, the pH scale can be used directly to compare the strengths of acids (provided they are of equal molar concentration).
  • The higher the H+ concentration, the lower the pH value.
42
Q

Hypothesis using rates of reaction to determine strength of an acid / base

A

Strong acids will react more vigorously with metals/carbonates

43
Q

Explanation of difference in pH between strong and weak acids/bases

A
  • The reaction of acids depend on the concentration of H+ ions.
  • Reaction rate will be sped up with stronger acids.
44
Q

Difference between strength and concentration

A
  • How much an acid/basedisassociates in aqueous solution
  • Number of moles of acid/base in a certain volume.
45
Q

Definition of acid deposition

A

Process by which acid forming pollutants are deposited on the Earth’s surface

46
Q

What is the natural pH of rain? Why does it have that pH?

A

Rain is naturally acidic due to dissolved CO2 and has a pH of 5.6

47
Q

What is the pH of acid deposition? How is it formed?

A
  • It has a pH below 5.6
  • Acid deposition occurs when nitrogen or sulfur oxides dissolve in water to form HNO3, HNO2, H2SO4 and H2SO3.
48
Q

What are the sources of sulfur oxides?

A
  • Extracting metals from their ores
  • Burning of fossil fuels (e.g., coal / heavy oil)
49
Q

Chemical equation for the formation of sulfur oxides from combustion reactions

A
  • S(s) + O2(g) => SO2(g)
  • 2SO2(g) + 02(g) => 2SO3(g)
50
Q

Chemical equation for the dissolution of sulfur oxides in water

A
  • H2O(l) + SO2(g) => H2SO3(aq)
  • H2O(l) + SO3(g) => H2SO4(aq)
51
Q

What is the source of nitrogen oxide?

A

Internal combustion engines

52
Q

Chemical equation for the formation of nitrogen oxides from combustion reactions

A
  • N2(g) + O2(g) => 2NO(g)
  • 2NO(g) + O2(g) => 2NO2(g)
53
Q

Chemical equation for the dissolution of nitrogen oxides in water

A

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

54
Q

Effects of acid deposition

A
  • Impact on materials
    = Expansion and stress in stonework
    = Erosion of structures
    = Corrosion reaction (Rusting)
  • Impact on the environment / human health
55
Q

Expansion and stress in stonework

a) Chemical equation for the reaction of SO2(g) and CaCO3(s)

A

2CaCO3(s) + 2SO2(g) + O2(g) => 2CaSO4(aq) + 2CO2(g)

56
Q

Erosion of structures

a) Chemical equation for the reaction of CaCO3 and H2SO4 / HNO3

A
  • CaCO3(s) + H2SO4(aq) => CaSO4(aq) + CO2(g) + H2O(l)
  • CaCO3(s) + 2HNO3(aq) => Ca(NO3)2 (aq) + C02(g) + H2O(l)
57
Q

Corrosion reaction
a) Chemical equation for the reaction of Fe and SO2

A
  • Fe(s) + SO2(g) + O2(g) => FeSO4(s)
58
Q

Corrosion reaction
a) Chemical equation for the reaction of Fe and H2SO4
b) Chemical equation for the reaction of Al2O3 and 6HNO3

A

a) Fe(s) + H2SO4(aq) => FeSO4(aq) + H2(g)
b) Al2O3(s) + 6HNO3(aq) => 2Al(NO3)3 + 3H2O(l)

59
Q

Impacts of acid deposition on environment

A
  • Displaces metal ions from soil and prevents the growth / development of plants
  • Elevates acid levels in lakes and rivers, affect pH sensitive ecosystems
60
Q

Impacts of acid deposition on human health

A
  • Causes the poisoning of fish, eventually resulting in damage to human health
  • Irritates mucous membrane causing respiratory illness (asthma)
61
Q

Methods used to reduce SO2 emissions

A
  • Pre-combustion
  • Post-combustion
62
Q

Precombustion methods used to reduce SO2 emissions

A

Hydrodesulfurization (HDS) is a catalytic process that removes sulfur from refined petroleum products by reacting it with hydrogen to form H2S, which is used to manufacture H2SO4

63
Q

Postcombustion methods used to reduce SO2 emissions

A

Flue-gas desulfurization can remove up to 90% of SO2 from flue gas in the smokestacks of coal-fired power stations before it is released into the atmosphere

Chemistry (12 decks)

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