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?

It converts to H2O. Signup and view all the answers

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

CH3NH2 and OH- Signup and view all the answers

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

HCl Signup and view all the answers

A Lewis acid is a substance that donates electron pairs.

False Signup and view all the answers

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

The charge decreases by +1. Signup and view all the answers

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

basic Signup and view all the answers

Match the following acids with their corresponding conjugate bases:

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

What defines a Brønsted acid?

Donates H+ ions Signup and view all the answers

A Lewis base donates electrons.

True Signup and view all the answers

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

The conjugate base becomes weaker. Signup and view all the answers

A solution with a pH of 14 is classified as _____

basic Signup and view all the answers

Match the following acids with their corresponding conjugate bases:

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

Which factor represents the influence of the charge on acidity?

Charge Signup and view all the answers

More negatively charged compounds are considered more acidic.

False Signup and view all the answers

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

Acidity increases. Signup and view all the answers

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

down Signup and view all the answers

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

sp = 50% sp2 = 33% sp3 = 25% Signup and view all the answers

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

Octane Signup and view all the answers

Which functional groups are present in the molecule?

Chloro and fluoro Signup and view all the answers

How are the substituents incorporated into the IUPAC name?

In alphabetical order Signup and view all the answers

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

By identifying the most significant functional group Signup and view all the answers

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

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

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

Protonated form Signup and view all the answers

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

Having a more electronegative atom bonded to a hydrogen Signup and view all the answers

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

2 Signup and view all the answers

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

They exist in their neutral zwitterion form. 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?

It will remain protonated. Signup and view all the answers

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

Stable conjugate bases strengthen the corresponding acid. Signup and view all the answers

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

Both will be deprotonated. Signup and view all the answers

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

They turn blue litmus paper red. Signup and view all the answers

What characterizes a strong acid compared to a weak acid?

It completely dissociates in solution. Signup and view all the answers

What is the pH range of basic solutions?

Greater than 7 Signup and view all the answers

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

They generate positive and negative ions in solution. Signup and view all the answers

Which statement about the pH scale is true?

The pH scale ranges from 0 to 14. Signup and view all the answers

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

Nonpolar Molecule Signup and view all the answers

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

False Signup and view all the answers

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

Nonpolar solvent Signup and view all the answers

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

nonpolar Signup and view all the answers

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

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 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.