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?

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

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

Increased acidity of hydrohalic acids. Signup and view all the answers

Which statement correctly describes a Brønsted-Lowry acid?

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

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

The stronger the acid, the weaker its conjugate base. Signup and view all the answers

Which of the following correctly identifies a diprotic acid?

H2CO3 Signup and view all the answers

Which ion is classified as a strong base?

OH– Signup and view all the answers

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

H2CO3 Signup and view all the answers

What defines a strong acid?

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

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

CH3COOH Signup and view all the answers

What is the charge of the conjugate base of HI?

Negatively charged Signup and view all the answers

What characterizes a weak acid?

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

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

The stronger acid gives the weaker conjugate base. Signup and view all the answers

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

The temperature of the solution. Signup and view all the answers

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

Higher electronegativity leads to a more stable anion. Signup and view all the answers

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

On the side of the weaker acid and weaker base. Signup and view all the answers

Which statement about weak bases is true?

Ammonia is an example of a weak base. Signup and view all the answers

What factor contributes to the acidity of an acid HA?

The stability of the anion A– Signup and view all the answers

Why are carboxylic acids stronger acids compared to alcohols?

Carboxylic acids have lower pKa values than alcohols Signup and view all the answers

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

The electronegativity and resonance stabilization. Signup and view all the answers

What role does resonance play in the stability of anions?

It increases the overall acidity of the compound Signup and view all the answers

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

4 out of every 1000 molecules. Signup and view all the answers

How does atomic radius affect the stability of halide ions?

Larger atomic radius increases anion stability Signup and view all the answers

Which halide ion has the largest atomic radius?

I– Signup and view all the answers

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

Stability increases due to less charge density Signup and view all the answers

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

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

What is the pKa range for most alcohols?

15 to 18 Signup and view all the answers

What is defined as an Arrhenius acid?

A substance that produces hydronium ions in water Signup and view all the answers

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

NaOH Signup and view all the answers

How do many metal hydroxides behave when dissolved in water?

They separate into their respective ions Signup and view all the answers

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

It can act as both an acid and a base Signup and view all the answers

What is a conjugate acid?

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

What characterizes a conjugate acid-base pair?

They can interconvert by the transfer of a proton Signup and view all the answers

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

They react immediately with water to form hydronium ions Signup and view all the answers

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

It involves the donation of a proton from an acid to a base 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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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.