Bronsted-Lowry Bases Quiz
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Questions and Answers

Which statement correctly describes a Brønsted-Lowry acid?

  • A substance that undergoes oxidation.
  • A substance that accepts electrons.
  • A substance that donates protons. (correct)
  • A substance that neutralizes bases.

    • What role does CH3NH2 play in the equilibrium CH3NH2 + H2O ⇌ CH3NH3+ + OH-?

  • It serves as a solvent.
  • It acts as a Brønsted-Lowry acid.
  • It acts as a Brønsted-Lowry base. (correct)
  • It participates as a product.

    • What does the term 'amphoteric' refer to in the context of water in the reaction?

  • It has a fixed role in chemical reactions.
  • It can participate as both an acid and a base. (correct)
  • It can only donate protons.
  • It always exists as H2O.

    • In the reaction, what is the outcome when OH- gains a proton?

    <p>It converts to H2O.</p> Signup and view all the answers

    Which of the following correctly identifies both Brønsted-Lowry bases in the reaction?

    <p>CH3NH2 and OH-</p> Signup and view all the answers

    Which of the following substances is a Brønsted acid in the reaction HCl + H2O → Cl- + H3O+?

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

    A Lewis acid is a substance that donates electron pairs.

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

    What happens to the charge of an acid when it forms its conjugate base?

    <p>The charge decreases by +1.</p> Signup and view all the answers

    A solution with a pH greater than 7.0 is classified as _____

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

    Match the following acids with their corresponding conjugate bases:

    <p>HCl = Cl- H2O = H3O+ H2SO4 = HSO4- NH4+ = NH3</p> Signup and view all the answers

    What defines a Brønsted acid?

    <p>Donates H+ ions</p> Signup and view all the answers

    A Lewis base donates electrons.

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

    What happens to the strength of a conjugate base as the strength of its corresponding acid increases?

    <p>The conjugate base becomes weaker.</p> Signup and view all the answers

    A solution with a pH of 14 is classified as _____

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

    Match the following acids with their corresponding conjugate bases:

    <p>HCl = Cl- H2SO4 = HSO4- H3O+ = H2O NH4+ = NH3</p> Signup and view all the answers

    Which factor represents the influence of the charge on acidity?

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

    More negatively charged compounds are considered more acidic.

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

    What happens to acidity as you move left-to-right across a row in the periodic table?

    <p>Acidity increases.</p> Signup and view all the answers

    The acidity of a compound increases as you go _____ down a column on the periodic table.

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

    Match the following hybridization types with their s-character percentage:

    <p>sp = 50% sp2 = 33% sp3 = 25%</p> Signup and view all the answers

    What is the correct parent chain for the molecule containing Cl and F?

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

    Which functional groups are present in the molecule?

    <p>Chloro and fluoro</p> Signup and view all the answers

    How are the substituents incorporated into the IUPAC name?

    <p>In alphabetical order</p> Signup and view all the answers

    Which of the following describes how to determine the highest priority functional group?

    <p>By identifying the most significant functional group</p> Signup and view all the answers

    What happens to an acid when it forms its conjugate base?

    <p>It loses a proton and decreases its charge by +1.</p> Signup and view all the answers

    At low pH, what form do amino acids generally take?

    <p>Protonated form</p> Signup and view all the answers

    Using the CARDIO mnemonic, which factor would most likely enhance the acidity of a compound?

    <p>Having a more electronegative atom bonded to a hydrogen</p> Signup and view all the answers

    Which of the following pK values corresponds to a typical carboxylic acid?

    <p>2</p> Signup and view all the answers

    At physiological pH (around 7.4), what can be said about the nature of amino acids?

    <p>They exist in their neutral zwitterion form.</p> Signup and view all the answers

    If the pK of a group's deprotonation is above the pH, what is the expected state of that group?

    <p>It will remain protonated.</p> Signup and view all the answers

    Which of the following statements about the strength of acids and bases is true regarding resonance?

    <p>Stable conjugate bases strengthen the corresponding acid.</p> Signup and view all the answers

    What form will the amine and side chain of histidine take at pH 8, given their pK values?

    <p>Both will be deprotonated.</p> Signup and view all the answers

    Which of the following statements accurately describes a property of acids?

    <p>They turn blue litmus paper red.</p> Signup and view all the answers

    What characterizes a strong acid compared to a weak acid?

    <p>It completely dissociates in solution.</p> Signup and view all the answers

    What is the pH range of basic solutions?

    <p>Greater than 7</p> Signup and view all the answers

    Which of the following best explains the conductivity property of both acids and bases in solution?

    <p>They generate positive and negative ions in solution.</p> Signup and view all the answers

    Which statement about the pH scale is true?

    <p>The pH scale ranges from 0 to 14.</p> Signup and view all the answers

    Which molecule would have the highest Rf in thin-layer chromatography?

    <p>Nonpolar Molecule</p> Signup and view all the answers

    In thin-layer chromatography, polar compounds travel the farthest up the plate.

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

    What type of solvent is typically used in thin-layer chromatography?

    <p>Nonpolar solvent</p> Signup and view all the answers

    In TLC, the greater the distance a compound travels, the more ____ it is.

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

    Match the following characteristics with their descriptions in thin-layer chromatography:

    <p>Polar compounds = Travel shorter distances up the plate Nonpolar compounds = Travel farther distances up the plate Rf value = Indicates a compound's solubility and polarity TLC plate = Coated with a polar substance</p> Signup and view all the answers

    Study Notes

    Brønsted-Lowry Bases in Equilibrium

    • Reaction: CH3NH2 + H2O ⇌ CH3NH3+ + OH-
    • CH3NH2 and OH- are the two Brønsted-Lowry bases in the reaction.
    • CH3NH2 accepts a proton to form CH3NH3+, making it a Brønsted-Lowry base.
    • OH- accepts a proton to revert to H2O, qualifying it as a Brønsted-Lowry base as well.

    Definitions

    • A Brønsted-Lowry Base is a substance that accepts protons (H+).
    • A Brønsted-Lowry Acid is a substance that donates protons.

    Reaction Analysis

    • The left-to-right direction shows CH3NH2 gaining a proton.
    • In the reverse direction, OH- gains a proton to become H2O.

    Properties of Water

    • Water (H2O) is amphoteric, meaning it can act as either an acid or a base.
    • It can form hydronium ions (H3O+) or hydroxide ions (OH-).

    Key Takeaway

    • Brønsted-Lowry theory distinguishes between proton donors (acids) and proton acceptors (bases).

    Brønsted Acids and Bases

    • Brønsted acid: substance that donates H⁺ ions (protons).
    • Brønsted base: substance that accepts H⁺ ions.
    • Example reaction: HCl + H₂O → Cl⁻ + H₃O⁺
      • HCl acts as a Brønsted acid (donor).
      • H₂O acts as a Brønsted base (acceptor).

    Lewis Acids and Bases

    • Lewis acid: substance that accepts an electron pair.
    • Lewis base: substance that donates an electron pair.
    • Defines acid-base interactions in terms of electron transfer, differing from the Brønsted theory.

    Conjugate Acids and Bases

    • Conjugate base: product formed from the acid in a reaction.
    • Conjugate acid: product formed from the base in a reaction.
    • Examples:
      • HCl → Cl⁻ (conjugate base)
      • H₂O → H₃O⁺ (conjugate acid).
    • Conjugate relationship:
      • Remove one H⁺ from an acid to find its conjugate base.
      • Add one H⁺ to a base to find its conjugate acid.

    Strength Relationship

    • Stronger acids have weaker conjugate bases.
    • Stronger bases have weaker conjugate acids.
    • Example: A strong acid like HCl has Cl⁻ as a weak conjugate base.

    pH Scale

    • pH measures the acidity or basicity of a solution.
    • Scale ranges from 0 to 14:
      • pH 7.0: neutral
      • pH < 7.0: acidic
      • pH > 7.0: basic.

    K and pK Values

    • K: measure of acid strength.
    • pK: measure of base strength.
    • Low pK indicates a strong acid, while high pK indicates a weak acid.
    • Low pK for bases indicates strong bases; high pK suggests weak bases.

    Brønsted Acids and Bases

    • Brønsted acid: substance that donates H⁺ ions (protons).
    • Brønsted base: substance that accepts H⁺ ions.
    • Example reaction: HCl + H₂O → Cl⁻ + H₃O⁺
      • HCl acts as a Brønsted acid (donor).
      • H₂O acts as a Brønsted base (acceptor).

    Lewis Acids and Bases

    • Lewis acid: substance that accepts an electron pair.
    • Lewis base: substance that donates an electron pair.
    • Defines acid-base interactions in terms of electron transfer, differing from the Brønsted theory.

    Conjugate Acids and Bases

    • Conjugate base: product formed from the acid in a reaction.
    • Conjugate acid: product formed from the base in a reaction.
    • Examples:
      • HCl → Cl⁻ (conjugate base)
      • H₂O → H₃O⁺ (conjugate acid).
    • Conjugate relationship:
      • Remove one H⁺ from an acid to find its conjugate base.
      • Add one H⁺ to a base to find its conjugate acid.

    Strength Relationship

    • Stronger acids have weaker conjugate bases.
    • Stronger bases have weaker conjugate acids.
    • Example: A strong acid like HCl has Cl⁻ as a weak conjugate base.

    pH Scale

    • pH measures the acidity or basicity of a solution.
    • Scale ranges from 0 to 14:
      • pH 7.0: neutral
      • pH < 7.0: acidic
      • pH > 7.0: basic.

    K and pK Values

    • K: measure of acid strength.
    • pK: measure of base strength.
    • Low pK indicates a strong acid, while high pK indicates a weak acid.
    • Low pK for bases indicates strong bases; high pK suggests weak bases.

    Factors Influencing Acidity

    • Use the mnemonic CARDIO to remember the key factors: Charge, Atom, Resonance, Dipole Induction, Orbital Hybridization, Other factors.

    Charge

    • Positively charged compounds are generally more acidic.
    • Negatively charged compounds tend to be more basic.
    • Examples:
      • HO⁻ (Charge: -1, pK Value: 15.7)
      • H₂O (Charge: 0, pK Value: 7.0)
      • H₃O⁺ (Charge: +1, pK Value: -1.7)

    Atom

    • Acidity increases left-to-right across a periodic table row.
    • Acidity also increases down a column on the periodic table.
    • Examples:
      • CH₄ (C, pK Value: 48)
      • NH₃ (N, pK Value: 38)
      • H₂O (O, pK Value: 15.7)
      • HF (F, pK Value: 3.2)

    Resonance

    • Resonance increases the stability of charged species.
    • More stable conjugate bases correspond to weaker acids.
    • Examples:
      • Alcohol 1 (No resonance, pK Value: 16)
      • Alcohol 2 (Resonance, pK Value: 10)

    Dipole Induction

    • Electronegative groups enhance acidity, while electron-donating groups reduce it.
    • Examples:
      • CH₃F (Withdrawing group, pK Value: 25)
      • CH₃CH₃ (Donating group, pK Value: 48)

    Orbital Hybridization

    • Increased s-character in an atom raises its electronegativity, leading to greater acidity.
    • More s-character results in a more acidic hydrogen bond.
    • Hybridization examples:
      • sp³ (25% s-character, Low electronegativity, pK Value: 48)
      • sp² (33% s-character, Medium electronegativity, pK Value: 44)
      • sp (50% s-character, High electronegativity, pK Value: 25)

    Summary of Orbital Hybridization and Acidity

    • The more s-character in hybridization, the more acidic the connected H will be.
    • Data shows a decrease in pK value as s-character increases:
      • sp³ (pK 25),
      • sp² (pK 16),
      • sp (pK 48).

    Molecular Identification

    • The correct IUPAC name for the molecule is 3-chloro-3-fluoro-2,2-dimethyl-4-propyloctane.
    • The longest continuous carbon chain contains 8 carbons, indicating the parent chain is octane.

    Functional Groups

    • The molecule features two key functional groups: chlorine (Cl) and fluorine (F).
    • Functional groups are located on carbon 3, leading to the use of "3-chloro" and "3-fluoro" in the name.

    Naming Process

    • Carbons are numbered from left to right to provide the lowest numbers to Cl and F locations.
    • Substituents include:
      • Two methyl groups on carbon 2 (noted as "2,2-dimethyl").
      • A propyl group on carbon 4 ("4-propyl").

    Naming Conventions

    • In naming polyfunctional compounds, identify the highest priority functional group first.
    • The parent chain corresponds to the longest chain that includes the primary functional groups.
    • Other functional groups or substituents are named in alphabetical order.

    Key Concepts

    • Properly numbering the carbon chain ensures accurate representation of substituents.
    • Understanding of priority functional groups is crucial for correct IUPAC naming.

    Conjugate Acids and Bases

    • Conjugate base is formed when an acid donates a proton (H+).
    • Conjugate acid is formed when a base accepts a proton (H+).
    • To derive a conjugate base, remove one proton from the acid and increase its charge by +1.
    • To derive a conjugate acid, add one proton to the base and increase its charge by +1.

    Sorting Acids and Bases by Strength

    • Use the mnemonic CARDIO to assess acidity:
      • Charge: More positive charge indicates higher acidity.
      • Atom: More electronegative atoms enhance acidity.
      • Resonance: Increased stability of the conjugate base leads to a stronger acid.
      • Dipole Induction: Electron-withdrawing groups enhance acidity; donating groups reduce it.
      • Induction: Higher s-character in atoms increases acidity of bonded H atoms.
      • Orbital Hybridization: Higher s-character suggests greater acidity of bonded H atoms.

    Important pK Values

    • Typical sp3-hybridized acid has a pK of 16.
    • Typical sp2-hybridized acid has a pK of 10.
    • Typical sp-hybridized acid has a pK of 5.
    • Typical carboxylic acid has a pK of 2.
    • Typical amine has a pK of 20.

    Amino Acids and pK Values

    • Amino acids consist of a carboxylic acid group and an amine group.
    • pK values determine overall charge of amino acids:
      • Carboxylic acid pK: 2
      • Amine pK: 9-10

    Amino Acids and pH

    • Amino acids are charged at physiological pH (around 7.4).
    • Low pH: Amino acids are protonated.
    • Neutral pH: Amino acids exist as zwitterions (both positive and negative charges present).
    • High pH: Amino acids are deprotonated.

    Predicting an Amino Acid's Form

    • To determine an amino acid's form at a specific pH:
      • If pK < pH, the group is deprotonated.
      • If pK > pH, the group is protonated.
    • Example with Histidine:
      • Carboxylic acid pK: 2.0
      • Side chain pK: 6.0
      • Amine pK: 9.0
      • At pH 4: Carboxylic acid and side chain are protonated; amine is deprotonated.
      • At pH 8: Carboxylic acid is deprotonated; side chain and amine are protonated.

    Properties of Acids

    • Sour taste, exemplified by citric acid found in lemons.
    • pH value generally falls below 7, indicating acidity.
    • React with metals, leading to the production of hydrogen gas.
    • Conduct electricity in aqueous solutions, functioning as electrolytes.
    • Turn blue litmus paper red in colorimetric tests.
    • Engage in neutralization reactions with bases, resulting in the formation of salts and water.

    Properties of Bases

    • Characterized by a bitter taste and slippery texture.
    • pH value typically exceeds 7, indicating basicity.
    • Can participate in neutralization reactions with acids.
    • Also conduct electricity in solution, acting as electrolytes.
    • Turn red litmus paper blue during pH testing.
    • Common examples include sodium hydroxide (NaOH) and calcium hydroxide (Ca(OH)₂).

    pH Scale

    • Ranges from 0 to 14, providing a measurement of acidity or basicity.
    • Acidic solutions are indicated by a pH value of less than 7.
    • A neutral solution, such as pure water, has a pH of exactly 7.
    • Basic solutions are characterized by a pH greater than 7.
    • The scale is logarithmic, meaning each unit change in pH reflects a tenfold change in hydrogen ion concentration.

    Strong vs Weak Acids and Bases

    • Strong acids, like hydrochloric acid (HCl) and sulfuric acid (H₂SO₄), fully dissociate in water.
    • Weak acids, such as acetic acid (CH₃COOH) and citric acid, exhibit partial dissociation in water.
    • Strong bases, including sodium hydroxide (NaOH) and potassium hydroxide (KOH), also fully dissociate.
    • Weak bases, such as ammonia (NH₃) and sodium bicarbonate (NaHCO₃), partially dissociate in water.
    • The strength of an acid or base is determined by its degree of ionization in solution, rather than its concentration.

    Thin-Layer Chromatography (TLC) Fundamentals

    • Thin-layer chromatography separates compounds based on solubility in a solvent.
    • The solvent moves up the TLC plate, carrying the compounds along with it.

    Solubility and Rf Value

    • The most soluble compounds travel the longest distance up the plate.
    • Compounds that are less soluble travel shorter distances, indicating greater polarity.
    • The Rf value (retention factor) correlates inversely with polarity:
      • Higher Rf value = more nonpolar compound
      • Lower Rf value = more polar compound

    Examining Compounds for Rf Values

    • Compounds listed for comparison:
      • Br
      • Br Br
      • OH
      • D
      • OH OH
    • To determine the compound with the highest Rf, the most nonpolar choice must be identified.

    Conclusion

    • Choice [D] is identified as the only nonpolar molecule among the options, thus it will have the highest Rf value in thin-layer chromatography.

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    Test your understanding of Bronsted-Lowry acids and bases with this quiz. You'll analyze the given equilibrium and identify which substances act as bases in the reaction. A great way to reinforce your knowledge of acid-base theory.

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