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Essential ideas:
- Many reactions involve the transfer of a proton from an acid to a base.
- The characterization of an acid depends on empirical evidence such as the production of gases in reactions with metals, the colour changes of indicators or the release of heat in reactions with metal oxides and hydroxides.
- The pH scale is an artificial scale used to distinguish between acid, neutral and basic/alkaline solutions.
- Increased industrialization has led to greater production of nitrogen and sulfur oxides leading to acid rain, which is damaging our environment. These problems can be reduced through collaboration with national and intergovernmental organizations.
8.1 Brønsted–Lowry acids and bases / conjugate acid-base pairs
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Understandings:
A Brønsted–Lowry acid is a proton/H+ donor and a Brønsted–Lowry base is a proton/H+ acceptor. Guidance: Students should know the representation of a proton in aqueous solution as both H+ (aq) and H3O+ (aq). |
8.1 Conjugate acid-base pairs
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Understandings:
A pair of species differing by a single proton is called a conjugate acid-base pair. Applications and skills: Deduction of the conjugate acid or conjugate base in a chemical reaction. |
8.1 Amphiprotic species
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Understandings:
Amphiprotic species can act as both Brønsted–Lowry acids and bases. Guidance: The difference between the terms amphoteric and amphiprotic should be covered. |
8.2 Reactions of acids and bases
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8.2 Reactions of acids and bases
Understandings: Most acids have observable characteristic chemical reactions with reactive metals, metal oxides, metal hydroxides, hydrogen carbonates and carbonates. Salt and water are produced in exothermic neutralization reactions. Applications and skills: Balancing chemical equations for the reaction of acids. Identification of the acid and base needed to make different salts. Guidance: Bases which are not hydroxides, such as ammonia, soluble carbonates and hydrogen carbonates should be covered. |
8.2 Thermometric titration
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This video covers how to calculate the concentration of a solution using a thermometric titration.
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8.3 The pH scale
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8.3 pH and change in hydrogen ion concentration
Understandings: pH = − log[H+(aq)] and [H+ ] = 10−pH . A change of one pH unit represents a 10-fold change in the hydrogen ion concentration [H+ ] pH values distinguish between acidic, neutral and alkaline solutions. |
8.3 Ionic product constant of water Kw
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8.3 Ionic product constant of water Kw
Understandings: pH values distinguish between acidic, neutral and alkaline solutions The ionic product constant, Kw = [H+ ][OH− ] = 10−14 at 298 K. |
8.4 Strong and weak acids and bases
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8.4 Strong and weak acids and bases
Understandings: Strong and weak acids and bases differ in the extent of ionization. A strong acid is a good proton donor and has a weak conjugate base. A strong base is a good proton acceptor and has a weak conjugate acid. Guidance: The terms ionization and dissociation can be used interchangeably. |
8.4 Strong and weak acids and bases
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8.4 Strong and weak acids and bases
Applications and skills: Distinction between strong and weak acids and bases in terms of the rates of their reactions with metals, metal oxides, metal hydroxides, metal hydrogen carbonates and metal carbonates and their electrical conductivities for solutions of equal concentrations. |
8.5 Acid deposition
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8.5 Acid deposition
Understandings: Rain is naturally acidic because of dissolved CO2 and has a pH of 5.6. Acid deposition has a pH below 5.0 Acid deposition is formed when nitrogen or sulfur oxides dissolve in water to form HNO3, HNO2, H2SO4 and H2SO3. Sources of the oxides of sulfur and nitrogen should be covered. Guidance: Balancing the equations that describe the combustion of sulfur and nitrogen to their oxides and the subsequent formation of H2SO3, H2SO4, HNO2 and HNO3. |
Please note that the syllabus now states that acid deposition has a pH of below 5.0.
8.5 Effects of acid deposition
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8.5 Effects of acid deposition
Understandings: The effects of acid deposition should be covered. Please note that I left out the effects on human health in the video, but it is covered in the worksheet. |
8.5 Reduction of SO2 and NOx emissions
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8.5 Reduction of SO2 and NOx emissions
Distinction between the pre-combustion and post-combustion methods of reducing sulfur oxides emissions. |
Further details about hydrodesulfurization: The oil based raw material is heated to 300-400°C and pumped under a pressure of up to 130 atm into a hydrodesulfurization reactor. The mixture passes over a catalyst which breaks the sulfur-carbon bonds, allowing the sulfur to react with the hydrogen to form hydrogen sulfide (H2S)