Arrhenius and Brønsted-Lowry Acids and Bases
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Questions and Answers

What characteristic of the iodide ion contributes to HI being the strongest acid?

  • The negative charge is localized over a small volume.
  • The presence of resonance in the structure.
  • The inductive effect of neighboring atoms.
  • The negative charge is delocalized over a larger volume. (correct)

    • Which statement accurately defines a Lewis acid?

  • A molecule that donates a pair of electrons.
  • A molecule that accepts a pair of electrons. (correct)
  • A molecule that forms hydrogen bonds.
  • A molecule that dissociates in water.

    • In which solvent does HCl utilize CH3OH as the strongest available Lewis base?

  • Acetic acid.
  • Water.
  • Methanol. (correct)
  • Ethanol.

    • What type of cation is referred to as a carbocation?

    <p>A carbon bonded to three atoms with a positive formal charge.</p> Signup and view all the answers

    What is the result of both resonance and the inductive effect discussed in the content?

    <p>Increased acidity of hydrohalic acids.</p> Signup and view all the answers

    Which statement correctly describes a Brønsted-Lowry acid?

    <p>It can donate protons and can be positively, negatively charged, or neutral.</p> Signup and view all the answers

    What is the relationship between the strength of an acid and its conjugate base?

    <p>The stronger the acid, the weaker its conjugate base.</p> Signup and view all the answers

    Which of the following correctly identifies a diprotic acid?

    <p>H2CO3</p> Signup and view all the answers

    Which ion is classified as a strong base?

    <p>OH–</p> Signup and view all the answers

    Which molecule can act as both an acid and a base?

    <p>H2CO3</p> Signup and view all the answers

    What defines a strong acid?

    <p>One that reacts almost completely with water to form H3O+.</p> Signup and view all the answers

    Between acetic acid and carbonic acid, which is the stronger acid?

    <p>CH3COOH</p> Signup and view all the answers

    What is the charge of the conjugate base of HI?

    <p>Negatively charged</p> Signup and view all the answers

    What characterizes a weak acid?

    <p>It partially dissociates in water to produce H3O+ ions.</p> Signup and view all the answers

    What is the relationship between stronger and weaker acids in an acid-base reaction?

    <p>The stronger acid gives the weaker conjugate base.</p> Signup and view all the answers

    Which factor does NOT influence the relative acidity of an organic acid?

    <p>The temperature of the solution.</p> Signup and view all the answers

    How does electronegativity affect the stability of the anion formed from an acid?

    <p>Higher electronegativity leads to a more stable anion.</p> Signup and view all the answers

    What is the expected position of equilibrium in an acid-base reaction involving a weak acid?

    <p>On the side of the weaker acid and weaker base.</p> Signup and view all the answers

    Which statement about weak bases is true?

    <p>Ammonia is an example of a weak base.</p> Signup and view all the answers

    What factor contributes to the acidity of an acid HA?

    <p>The stability of the anion A–</p> Signup and view all the answers

    Why are carboxylic acids stronger acids compared to alcohols?

    <p>Carboxylic acids have lower pKa values than alcohols</p> Signup and view all the answers

    What stabilizes the anion formed when an acid loses a proton?

    <p>The electronegativity and resonance stabilization.</p> Signup and view all the answers

    What role does resonance play in the stability of anions?

    <p>It increases the overall acidity of the compound</p> Signup and view all the answers

    In an aqueous solution, what percentage of acetic acid molecules are typically ionized?

    <p>4 out of every 1000 molecules.</p> Signup and view all the answers

    How does atomic radius affect the stability of halide ions?

    <p>Larger atomic radius increases anion stability</p> Signup and view all the answers

    Which halide ion has the largest atomic radius?

    <p>I–</p> Signup and view all the answers

    What happens to the stability of the anion as the atomic radii of the elements increase?

    <p>Stability increases due to less charge density</p> Signup and view all the answers

    Which of the following describes the inductive polarization of electron density?

    <p>It occurs when a nearby atom with higher electronegativity pulls electron density</p> Signup and view all the answers

    What is the pKa range for most alcohols?

    <p>15 to 18</p> Signup and view all the answers

    What is defined as an Arrhenius acid?

    <p>A substance that produces hydronium ions in water</p> Signup and view all the answers

    Which of the following compounds is an example of an Arrhenius base?

    <p>NaOH</p> Signup and view all the answers

    How do many metal hydroxides behave when dissolved in water?

    <p>They separate into their respective ions</p> Signup and view all the answers

    What role does water play in the Brønsted-Lowry acid-base theory?

    <p>It can act as both an acid and a base</p> Signup and view all the answers

    What is a conjugate acid?

    <p>The species formed when a proton is gained by a base</p> Signup and view all the answers

    What characterizes a conjugate acid-base pair?

    <p>They can interconvert by the transfer of a proton</p> Signup and view all the answers

    What happens to H+ ions when they are in aqueous solution according to modern understanding?

    <p>They react immediately with water to form hydronium ions</p> Signup and view all the answers

    Which statement regarding the transfer of protons in acid-base reactions is accurate?

    <p>It involves the donation of a proton from an acid to a base</p> Signup and view all the answers

    Study Notes

    Arrhenius Acids and Bases

    • Arrhenius proposed definitions in 1884
    • Acid: A substance that dissolves in water, producing hydronium ions (H₃O⁺)
    • Base: A substance that dissolves in water, producing hydroxide ions (OH⁻)
    • The definition of an acid is a slight modification of the original Arrhenius definition, which stated that an acid produces H⁺ in an aqueous solution. Modern understanding is that H⁺ reacts immediately with a water molecule, forming hydronium ion.

    Curved Arrows

    • Used to show electron pair movement during reactions
    • Example: HCl dissolving in water, forming hydronium ion and chloride ion
    • Electron pair from O-H bond moves to form a new O-H bond, resulting in hydronium ion and chloride ion.

    Arrhenius Bases

    • Many bases are metal hydroxides (e.g. KOH, NaOH, Mg(OH)₂, Ca(OH)₂)
    • These are ionic solids
    • When they dissolve/dissipate, they separate into ions

    Brønsted-Lowry Acids & Bases

    • Acid: A proton donor
    • Base: A proton acceptor
    • Conjugate acid: Formed when a base accepts a proton from an acid
    • Conjugate base: Formed when an acid donates a proton to a base

    Conjugate Acid-Base Pairs

    • Any pair of molecules or ions that can be interconverted by proton transfer
    • Example: reaction of hydrogen chloride (HCl) with water (H₂O)
      • HCl is an acid, donating a proton to water, forming chloride ion (Cl⁻)
      • Water is a base, accepting a proton, forming hydronium ion (H₃O⁺)

    Brønsted-Lowry Definitions

    • Brønsted-Lowry definitions do not require water as a reactant
    • Example: Reaction of acetic acid (CH₃COOH) and ammonia (NH₃)
      • Acetic acid (CH₃COOH) donates a proton to ammonia, forming acetate ion (CH₃COO⁻)
      • Ammonia (NH₃ ) accepts a proton, forming ammonium ion (NH₄⁺)

    Curved Arrow Explanation

    • Curved arrows show electron flow during proton transfers

    Acid Strength and Conjugate Strength

    • Strong acid: Reacts completely with water to form hydronium ions (H₃O⁺)
    • Strong base: Reacts completely with water to form hydroxide ions
    • Examples of common strong acids: HCl, HBr, HI, HNO₃, H₂SO₄, HClO₄
    • Examples of common strong bases: LiOH, NaOH, KOH, Ba(OH)₂

    Weak Acids

    • Weak acid: Only partially dissociates in water, producing hydronium ions (H₃O⁺)
    • Example: Acetic acid (CH₃COOH) partially dissociates into acetate ion (CH₃COO⁻) and hydronium ion (H₃O⁺)

    Weak Bases

    • Weak bases: Partially dissociate in water, producing hydroxide ions(OH⁻)
    • Example: Ammonia (NH₃) partially dissociates into ammonium ion (NH₄⁺) and hydroxide ion (OH⁻)

    Acid-Base Reactions

    • Acetic acid is only partially ionized in aqueous solution
    • The equilibrium equation for weak acid (HA) can be written as;
      • HA + H₂O ⇌ A⁻ + H₃O⁺
      • Ka = [H₃O⁺][A⁻] / [HA].

    pKa Values

    • Table 2.2 presents pKa values for various acids
    • pKa is a measure of acid strength, with smaller pKa values corresponding to stronger acids

    Acid-Base Equilibria

    • Equilibrium position depends on relative acid strengths among species involved
    • Stronger acid reacts with stronger base, producing weaker acid and base.
    • Equilibrium favours the side of the weaker acid and base

    Structure and Acidity

    • Factors affect acidic strength
      • Electronegativity of atom bonded to H
      • Resonance/delocalization in the anion formed
      • Inductive effects
      • Size/charge distribution of the anion

    Electronegativity

    • Higher electronegativity corresponds to greater stability
    • The higher the atoms electronegativity value, the better able it is to stabilize a negative charge.

    Resonance Delocalization

    • Resonance stabilization contributes to greater stability in an anion
    • Carboxylic acids are more acidic than alcohols because of resonance in carboxylare anion

    Inductive Effect

    • Inductive effect accounts for the impact of substituent groups on acidity

    Anion Stability

    • Anion stability is critical in determining acid strength
    • Greater stability of the anion formed increases the acid strength of the parent molecule

    Acidic Strength of Halides

    • Relative acidity of hydrogen halides (HI > HBr > HCl>HF)

    Lewis Acids & Bases

    • Lewis acid: A molecule or ion that can accept an electron pair to form a new covalent bond
    • Lewis base: A molecule or ion that can donate an electron pair to form a new covalent bond
    • Examples of proton transfers: HCl reacting with H₂O or CH₃OH

    Carbocation Example

    • Carbocation is one type of lewis acid, such as in the example of CH₃-CH⁺-CH₃

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    Acids and Bases Chapter 2 PDF

    Description

    Test your understanding of Arrhenius and Brønsted-Lowry definitions of acids and bases. Explore the concepts of hydronium and hydroxide ions, and practice using curved arrows to represent electron movement in reactions. This quiz will strengthen your grasp of fundamental acid-base theories.

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