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8 Acid and Bases

Kayla Schmidt English

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8 Acid and Bases

Brønsted-Lowry Acids and Bases
- Definition
  - Brønsted-Lowry acid= proton (H+) donor
  - Brønsted-Lowry Base= proton (H+) acceptor
- Conjugate acid-base pairs
  - Conjugate base losses a proton (H+)
  - Conjugte acid will gain the proton (H+) lost
Amphiprotic Species
- Species that can act as a Brønsted-Lowry acid or base
- Eg.
  - H2O
  - Hydrogen Carbonate ion (HCO3-)
- Must be able to donate a proton (H+) to another species and also be able to accept a proton (H+) from another species.
- Amphiprotic vs Amphoteric
  - Amphiprotic refers to any substance that can both donate and accept a proton (Brønsted-Lowry theory)
  - Amphoteric refers to any species that can act like an acid or a base.
    - Can be applied in different acid base theories where there is no proton transfer (eg. Lewis Theory)
  - All amphiprotic species are also amphoteric
Reactions of acids and bases
- Neutralization reactions with hydroxides (exothermic)
- Reactions with reactive metals (metals above copper)
  - Which acids form which salts:
    - Hydrochloric Acid (HCl)---> Chloride (Cl-)
    - Nitric Acid (HNO3)---> Nitrate (NO3-)
    - Sulfuric Acid (H2SO4)---> Sulfate (SO4^2-)
- Reactions with Carbonates
- Reactions with Hydrogen Carbonates
The pH Scale
- Measures how acidic or basic a substance is
- A change in one unit of pH represents a tenfold change in hydrogen ion concentration [H+]
  - Decrease in pH by one is a x10 increase of [H+]
  - Increase in pH by one is a x10 decrease is [H+]
Ionic product constant of water Kw
- Ionization of water
Strong and Weak Acids and Bases
- Acids
  - Strong Acids completely ionize/dissociate in solution
    - good proton donors and is therefore paired with a weak base in conjugate acids
  - Weak Acids partially ionize/dissociate in solution
    - use equilibrium sign to show it only partially dissociates
    - poor proton donors and therefore are paired with stronger conjugate bases
- Bases
  - Strong bases completely ionize/dissociate in solution
    - good proton acceptors and therefore are paired with weak conjugate acids
  - Weak bases partially ionize/dissociate in solution
    - poor proton acceptors and therefore paired with stronger conjugate acids
- Distinguishing between them
  - Conductivity
    - Strong acids and bases have a higher concentration of mobile ions in solution, therefore they have a higher electrical conductivity than weak acids and bases (of equal concentration)
  - Rate of Reaction
    - Strong acids have a higher rate of reaction with reactive metals (those above copper) than weak acids (of equal concentration) because they have a higher concentration of H+ ions in solution
  - pH
    - Strong acids have a lower pH than weak acids (of equal concentration) because they have a higher concentration of H+ ions in solution
Acid Deposition
- Rain water is naturally acidic at a pH of 5.6
  - CO2 in the atmosphere makes it slightly acidic
- Acid rain has a pH of less than 5.0
- Types of Acid Deposition
  - Wet
    - Includes acid rain, fog and snow
  - Dry
    - Includes acidic gases and particules
- Caused by acidic gases
  - Eg
    - SO2
      - Man Made sources: Power stations
      - Natural sources: volcanoes
    - NOx
      - Man Made Sources: Engins
  - these dissolve in water to form acids
    - Such As: H2SO3, H2SO4, HNO2, HNO3
- Formation of sulfurus and sulfuric acid
- Formation of nitrus and nitric acid
  - high temperatures in internal combustion engines
- Effects of acid deposition
  - Effects on materials
    - Statues get damaged
      - CaCO3 is found in marble and limestone
  - Effects on plants
    - acid rain leaches important nutrients such as Mg^2+, Ca^2+, K+ ions from the soil
      - without these nutrients, plants are unable to grow
    - alcid rain releases Al^3+ ions from rocks into soil. Al^3+ ions damage roots of plants and prevent them from taking up water and nutrients
  - Effects on water
    - Fish at pH below 5.
    - The Al^3+ ions in rocks are released and interfere with the operation of a fish's gills and reduce their ability to take in oxygen.
    - nitrates in nitric acid can cause eutrophication in lakes
  - Effects on Humans
    - breathing acidic gases can irritate the respiratory tract
    - increased risk of respiratory diseases such as asthma, bronchitis and emphysema
    - greater risk of poisonous metal ions such as Pb^2+ and Cu^2+ being released from water pipes
- Reduction of SO2 and NOx emissions
  - SO2
    - Pre-combustion methods
      - Hydrodesulfurization
        a chemical process that uses a catalyst to remove sulfur from natural gas and fro refined petroleum products.
      - Fluidized Bed Combustion
        coal is mixed with powdered limestone (caCO3) during combustion
    - Pre-combustion methods
      - Flu-Gas Desulfurization
        Can remove up to 90% of SO2 emissions from power stations
  - NOx
    - Catalytic converters
      - convert CO and NO to CO2 and N
      - hot exhaust gases are mixed with air and passed over a platinum (Pt) or palladium (Pd) catalyst
    - Exhaust gas recirculation
      - Recirculates exhaust gases back into the engine which lowers the operating temperature and reduces nitrogen oxide emissions.
  - powdered CaCO3 is added to lakes to reduce the acidity. CaO and CA(OH)2 are also used to neutralize acidic water.