Bronsted-Lowry Bases Quiz

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.