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

Topic 8: Acids and Bases Flashcards by Shreya Sumesh

Bronsted-Lowry acid

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

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Bronsted-Lowry base

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

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Conjugate acid-base pair definiton

A pair of species differing by a single proton

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An acid becomes into …

conjugate base

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A base becomes into a …

conjugate acid

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Amphiprotic definition

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

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Example of amphiprotic substance

H2O (H3O+ / OH-)

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Amphoteric definiton

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

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Relationship between amphoteric and amphiprotic reactions

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

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Equation of reaction of an acid with a metal

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

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Which type of metals do acids react with?

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

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Neutralization reaction

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

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Why are neutralization reactions exothermic?

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

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

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Equation of reaction of an acid with carbonate and hydrogen carbonate

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

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Indicator definition

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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Common indicators (Acid => Base)

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

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Why does water self-ionize?

Due to its amphoteric nature

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Chemical equation of ionization of water

2H2O(l) ⇌ H3O+(aq) + OH-(aq)

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Ionization constant of water (Kw)

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

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

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

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Formulas for calculating pH and pOH from their concentrations

pH = -log[H+]
pOH = -log[OH-]

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Formula for calculating pKw at 298 K

pKw = pH + pOH = 14.00

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Acidity of a solution when pH is:

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

a) Neutral
b) Acidic
c) Basic

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

tenfold change

Methods to measure pH

- Universal indicator - pH meter

Functioning of universal indicator

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

Functioning of pH meter

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

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

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

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

Strong acids/bases

7 strong acids

- HCL - HNO3 - H2SO4 - HBr - HI - HClO4 - HClO3

Examples of weak acids

- CH3COOH - H2CO3 - C₃H₆O₂ - H3PO4

Examples of strong bases

- Group 1 Hydroxides - Ba(OH)2

Examples of weak bases (2)

- NH3 (Ammonia) - C2H5NH2

Definition of a strong acid

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

Definition of a strong base

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

Experimental techniques used to determine acid / base strengths

a) Conductivity b) pH c) Rates of reaction

Hypothesis using conductivity to determine strength of an acid / base

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

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

- 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.

Hypothesis using pH to determine strength of an acid / base

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

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

- 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.

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

Strong acids will react more vigorously with metals/carbonates

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

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

Difference between strength and concentration

- How much an acid/basedisassociates in aqueous solution - Number of moles of acid/base in a certain volume.

Definition of acid deposition

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

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

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

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

- 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.

What are the sources of sulfur oxides?

- Extracting metals from their ores - Burning of fossil fuels (e.g., coal / heavy oil)

Chemical equation for the formation of sulfur oxides from combustion reactions

- S(s) + O2(g) => SO2(g) - 2SO2(g) + 02(g) => 2SO3(g)

Chemical equation for the dissolution of sulfur oxides in water

- H2O(l) + SO2(g) => H2SO3(aq) - H2O(l) + SO3(g) => H2SO4(aq)

What is the source of nitrogen oxide?

Internal combustion engines

Chemical equation for the formation of nitrogen oxides from combustion reactions

- N2(g) + O2(g) => 2NO(g) - 2NO(g) + O2(g) => 2NO2(g)

Chemical equation for the dissolution of nitrogen oxides in water

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

Effects of acid deposition

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

Expansion and stress in stonework a) Chemical equation for the reaction of SO2(g) and CaCO3(s)

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

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

- CaCO3(s) + H2SO4(aq) => CaSO4(aq) + CO2(g) + H2O(l) - CaCO3(s) + 2HNO3(aq) => Ca(NO3)2 (aq) + C02(g) + H2O(l)

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

- Fe(s) + SO2(g) + O2(g) => FeSO4(s)

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

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

Impacts of acid deposition on environment

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

Impacts of acid deposition on human health

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

Methods used to reduce SO2 emissions

- Pre-combustion - Post-combustion

Precombustion methods used to reduce SO2 emissions

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

Postcombustion methods used to reduce SO2 emissions

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

Topic 8: Acids and Bases Flashcards

(63 cards)