Arrhenius Acids and Bases Overview
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Questions and Answers

Which acid is considered the strongest due to the delocalization of negative charge?

  • HBr
  • HI (correct)
  • HF
  • HCl

A Lewis base can form a new covalent bond by accepting a pair of electrons.

False (B)

What type of reaction occurs when HCl dissolves in water?

Proton-transfer reaction

An organic cation where a carbon is bonded to three atoms and carries a positive charge is called a _______.

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

Match the acid with its dissolution medium:

<p>HCl = Methanol HI = Water HF = Methanol</p> Signup and view all the answers

What does an Arrhenius acid produce when dissolved in water?

<p>Hydronium ions (H3O+) (D)</p> Signup and view all the answers

According to the Arrhenius definition, bases produce hydronium ions in water.

<p>False (B)</p> Signup and view all the answers

What is the term for a substance that acts as a proton donor according to the Brønsted-Lowry definition?

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

A substance that produces hydroxide ions (OH–) when dissolved in water is known as a __________.

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

Match the following terms with their definitions:

<p>Acid = Proton donor Base = Proton acceptor Conjugate acid = Species formed from a base after it accepts a proton Conjugate base = Species formed from an acid after it donates a proton</p> Signup and view all the answers

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

<p>NaOH (D)</p> Signup and view all the answers

The conjugate acid of a base is the species that forms when the base donates a proton.

<p>False (B)</p> Signup and view all the answers

What is produced when hydrogen chloride (HCl) dissolves in water?

<p>Hydronium ions (H3O+) and chloride ions (Cl–)</p> Signup and view all the answers

Which of the following compounds is a stronger acid?

<p>Carboxylic acid (B)</p> Signup and view all the answers

Resonance stabilization increases the acidity of the compound.

<p>True (A)</p> Signup and view all the answers

What is the relationship between the stability of an anion and the acidity of its corresponding acid?

<p>The more stable the anion, the greater the acidity of the acid.</p> Signup and view all the answers

In terms of acid strength, the order of hydrogen halides is ___ > ___ > ___ > ___.

<p>HI, HBr, HCl, HF</p> Signup and view all the answers

Match the following anions with their corresponding atomic radius order:

<p>I– = Largest ionic radius Br– = Second largest ionic radius Cl– = Third largest ionic radius F– = Smallest ionic radius</p> Signup and view all the answers

Which of the following factors contributes to the acidity of an acid?

<p>Resonance stabilization of the anion (A)</p> Signup and view all the answers

I– has a smaller atomic radius than F–.

<p>False (B)</p> Signup and view all the answers

What phenomenon causes inductive polarization of electron density in acids?

<p>Presence of a nearby atom of higher electronegativity.</p> Signup and view all the answers

What defines a strong acid?

<p>It reacts completely with water to form H3O+ ions. (D)</p> Signup and view all the answers

All Brønsted-Lowry acids must be positively charged.

<p>False (B)</p> Signup and view all the answers

What are the three classifications of acids based on the number of protons they can donate?

<p>Monoprotic, diprotic, triprotic</p> Signup and view all the answers

The conjugate base of acetic acid (CH3COOH) is ______.

<p>acetate ion (CH3COO–)</p> Signup and view all the answers

Match the acid with its corresponding conjugate base:

<p>HCl = Cl– H2CO3 = HCO3– H3PO4 = H2PO4– HI = I–</p> Signup and view all the answers

What defines a weak acid?

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

Which statement is true regarding the relationship between acids and their conjugate bases?

<p>There is an inverse relationship between the strength of an acid and its conjugate base. (B)</p> Signup and view all the answers

Carbonic acid (H2CO3) can donate two protons to become ______ and then ______.

<p>bicarbonate ion (HCO3–), carbonate ion (CO3^2–)</p> Signup and view all the answers

A strong acid produces a stronger conjugate base.

<p>False (B)</p> Signup and view all the answers

Ammonia (NH3) can act as both an acid and a base.

<p>True (A)</p> Signup and view all the answers

Name an example of a weak base.

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

The ionization of a weak acid can be represented as HA ⇌ H+ + __________.

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

Match the terms with their definitions:

<p>Weak Acid = Partially dissociates in water to produce H3O+ ions Weak Base = Partially dissociates in water to produce OH– ions Conjugate Base = The species formed when an acid donates a proton Acidity = The tendency of a compound to donate H+ ions</p> Signup and view all the answers

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

<p>Molecular weight of the acid (A)</p> Signup and view all the answers

Equilibrium in acid-base reactions favors the formation of stronger acids and bases.

<p>False (B)</p> Signup and view all the answers

What happens to the stability of an anion as the electronegativity of the atom bearing the negative charge increases?

<p>The stability of the anion increases.</p> Signup and view all the answers

A Brønsted-Lowry acid must always be positively charged.

<p>False (B)</p> Signup and view all the answers

The stronger the acid, the stronger its conjugate base.

<p>False (B)</p> Signup and view all the answers

Carbonic acid can only donate one proton.

<p>False (B)</p> Signup and view all the answers

All strong acids completely ionize in water to form H3O+ ions.

<p>True (A)</p> Signup and view all the answers

Ammonia (NH3) acts exclusively as a Brønsted-Lowry base.

<p>False (B)</p> Signup and view all the answers

Acids produce hydroxide ions (OH–) when dissolved in water.

<p>False (B)</p> Signup and view all the answers

Brønsted-Lowry acids are defined as proton acceptors.

<p>False (B)</p> Signup and view all the answers

The species formed from an acid when it donates a proton is called a conjugate acid.

<p>False (B)</p> Signup and view all the answers

HCl dissolving in water leads to the formation of hydronium ions and chloride ions.

<p>True (A)</p> Signup and view all the answers

Bases that are not metal hydroxides produce hydroxide ions (OH–) by reacting with water molecules.

<p>True (A)</p> Signup and view all the answers

Acetic acid is a strong acid because it completely dissociates in water.

<p>False (B)</p> Signup and view all the answers

The position of equilibrium in an acid-base reaction lies on the side of the stronger acid.

<p>False (B)</p> Signup and view all the answers

Electronegativity affects the stability of an anion, with more electronegative atoms leading to more stable anions.

<p>True (A)</p> Signup and view all the answers

In acid-base reactions, the stronger acid reacts with the weaker base to produce stronger conjugate pairs.

<p>False (B)</p> Signup and view all the answers

Resonance stabilization is a factor that can enhance the acidity of an organic acid.

<p>True (A)</p> Signup and view all the answers

Flashcards

Arrhenius acid

A substance that dissolves in water to produce hydronium ions (H3O+).

Arrhenius base

A substance that dissolves in water to produce hydroxide ions (OH–).

Hydronium ion

H3O+, formed when an acid dissolves in water.

Brønsted-Lowry acid

A proton donor.

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Brønsted-Lowry base

A proton acceptor.

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Conjugate base

The species formed when an acid donates a proton.

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Conjugate acid

The species formed when a base accepts a proton.

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Acid-base reaction

A proton-transfer reaction.

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Conjugate Acid-Base Pair

Two substances related by the gain or loss of a proton.

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Strong Acid

Reacts almost completely with water to form H3O+ ions.

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Strong Base

Reacts almost completely with water to form OH- ions.

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Monoprotic Acid

An acid that can donate only one proton.

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Diprotic Acid

An acid that can donate two protons.

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Acid Strength & Conjugate Base Strength

Stronger acid = weaker conjugate base, and vice versa.

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Weak Acid

A substance that partially dissociates in water, producing few H3O+ ions.

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Weak Base

A substance that partially dissociates in water, producing few OH– ions.

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Acid-Base Equilibrium

The balance between acids and bases; dependent on the strength of the acid.

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Weaker Acid

An acid that less readily donates a proton, compared to a stronger acid.

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Anion Stability

Stability of the anion, A– forms after a proton is transferred to a base.

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Electronegativity Influence

Higher electronegativity of an atom in an acid increases its acidity as it stabilizes the negative charge on the anion.

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Resonance Stabilization

Electron delocalization amongst atoms in an anion makes the anion more stable and thus the acid stronger.

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Lewis acid

A molecule or ion that can form a new covalent bond by accepting a pair of electrons.

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Lewis base

A molecule or ion that can form a new covalent bond by donating a pair of electrons.

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What is the strongest Lewis base in water?

A water molecule (H2O) is the strongest Lewis base in water because it can donate a pair of electrons from its oxygen atom.

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What is a carbocation?

A positively charged carbon atom bonded to only three other atoms.

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Inductive effect

The ability of a substituent to withdraw or donate electron density through sigma bonds, affecting the charge distribution in a molecule.

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What is the trend of acidity with anions?

The more stable the anion A– is, the stronger the acid HA is.

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Resonance

The delocalisation of electron density over multiple atoms in a molecule, leading to increased stability.

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Carboxylic Acid vs. Alcohol

Carboxylic acids are stronger acids than alcohols because the carboxylate anion is resonance stabilized, while the alkoxide anion is not.

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Inductive Effect on Acid Strength

Electron-withdrawing groups increase acidity by stabilizing the conjugate base.

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What is the relationship of acid strength and anion size?

The larger the size of an anion, the more stable it is, making the corresponding acid stronger.

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Atomic Size Trend

Atomic size increases down a group and decreases across a period on the periodic table.

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Anion Size vs. Atomic Size

Anions are always larger than the atoms from which they are derived because the addition of electrons introduces new repulsions and expands the electron cloud.

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What does an Arrhenius acid produce in water?

An Arrhenius acid produces hydronium ions (H3O+) when dissolved in water.

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What does an Arrhenius base produce in water?

An Arrhenius base produces hydroxide ions (OH-) when dissolved in water.

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How does HCl act as an acid?

HCl reacts with water to form hydronium ions (H3O+) and chloride ions (Cl-) making it an Arrhenius acid.

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What is a conjugate acid-base pair?

A conjugate acid-base pair is any two molecules or ions that can be interconverted by transfer of a proton.

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Identify the conjugate acid and base in the reaction: HCl + H2O -> H3O+ + Cl-

H3O+ is the conjugate acid formed from the base H2O, and Cl- is the conjugate base formed from the acid HCl.

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pKa Value

A measure of the strength of an acid. Lower pKa values indicate stronger acids.

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Equilibrium in Acid-Base Reactions

The balance point between reactants and products in an acid-base reaction. The side with the weaker acid and weaker base will be favored.

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Factors Affecting Acidity

Factors influencing the strength of an acid, including electronegativity, resonance, inductive effect, and size/delocalization of charge in the anion.

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Study Notes

Arrhenius Acids and Bases

  • In 1884, Arrhenius defined acids as substances that dissolve in water to produce hydronium ions (H3O+).
  • Arrhenius defined bases as substances that dissolve in water to produce hydroxide ions (OH-).
  • This definition slightly modifies the original Arrhenius definition, where an acid produces H+ in aqueous solution.
  • Today, H+ immediately reacts with a water molecule to form hydronium.

Arrhenius Acids and Bases (Example)

  • HCl, when dissolved in water, reacts with water to produce a hydronium ion and a chloride ion.
  • The reaction is shown using curved arrows to depict electron pair movement.

Arrhenius Acids and Bases (Bases)

  • Many bases are metal hydroxides like KOH, NaOH, Mg(OH)2, and Ca(OH)2.
  • These are ionic solids that dissociate into their constituent ions when dissolved in water.

Brønsted-Lowry Acids and Bases

  • An acid is a proton donor.
  • A base is a proton acceptor.
  • Conjugate base: the species formed when an acid donates a proton to a base.
  • Conjugate acid: the species formed when a base accepts a proton from an acid.
  • Acid-base reactions involve proton transfer.
  • Conjugate acid-base pairs are interconvertible via proton transfer.

Conjugate Acids & Bases (Example)

  • HCl (acid) reacts with H₂O (base) to form Cl- (conjugate base of HCl) and H3O+ (conjugate acid of H₂O).

Brønsted-Lowry Acids and Bases (No Water)

  • The Brønsted-Lowry definitions don't require water as a reactant.
  • For example, acetic acid (CH3COOH) reacting with ammonia (NH3) forms acetate ion (CH3COO-) and ammonium ion (NH4+).

Brønsted-Lowry Acids & Bases (Further Explanation)

  • The reaction using curved arrows, showing electron flow during proton transfer, demonstrates how the reaction happens.

Table 2.1 (Some Acids and Their Conjugate Bases)

  • Acids can be positively, negatively, or neutrally charged (e.g., H3O+, H2CO3, H2PO4-).
  • Bases can be negatively or neutrally charged (e.g., OH-, Cl-, NH3).
  • Acids are classified as monoprotic, diprotic, or triprotic based on the number of protons they release (e.g., HCl, H2CO3, H3PO4).

Brønsted-Lowry Acids & Bases (Carbonic Acid)

  • Carbonic acid (H2CO3) can release one proton to form bicarbonate (HCO3-) and then a second proton to form carbonate (CO32-).

Brønsted-Lowry Acids & Bases (Relationship)

  • The strength of an acid is inversely related to the strength of its conjugate base.
  • The stronger the acid, the weaker its conjugate base (e.g., HI is stronger than CH3COOH).

Acid and Base Strength (Definitions)

  • Strong acid: reacts completely or almost completely with water to produce H3O+ ions.
  • Strong base: reacts completely or almost completely with water to produce OH- ions.
  • Examples include HCl, HBr, HI, HNO3, H2SO4, and HClO4 (acids). LIOH, NaOH, KOH, Ba(OH)2 (bases)

Acid and Base Strength (Weak)

  • Weak acid: partially dissociates in water, producing H3O+ ions (e.g., CH3COOH)
  • Weak base: partially dissociates in water, producing OH- ions (e.g., NH3).

Acid-Base Reactions (Ionization of Weak Acids)

  • Acetic acid is incompletely ionized in aqueous solutions.
  • The equation represents a weak acid ionizing (HA + H2O ⇌ A- + H3O+).
  • The equilibrium constant (Ka) relates the concentrations of reactants and products.

pKa Values

  • pKa values are used to compare the relative strength of acids; the smaller the pKa the stronger the acid.
  • pKa values for different types of organic and inorganic acids are listed and categorized.

Acid-Base Equilibria

  • The position of equilibrium in acid-base reactions is determined by comparing the strengths of the acids involved.
  • Stronger acid reacts with stronger base to produce weaker acid and weaker base.
  • Equilibrium lies on the side of weaker acid and weaker base.

Structure and Acidity (Key Factors)

  • Relative stability of the anion (A-) formed when the acid (HA) loses a proton.
  • Four factors are:
    • Electronegativity of the atom bonded to H in HA.
    • Resonance stabilization of A⁻.
    • Inductive effect.
    • Size and delocalization of charge in A⁻.

Structure and Acidity (Electronegativity)

  • Electronegativity of the atom bearing the negative charge affects the strength of acid; higher electronegativity leads to more stable anion.
  • Within a period, increasing electronegativity increases acidity.

Structure and Acidity (Resonance)

  • Compare the acidity of carboxylic acids and alcohols.
  • carboxylic acids are stronger acids than alcohols due to resonance stabilization of the carboxylate anion.

Structure and Acidity (Inductive Effect)

  • Inductive effect describes polarization of electron density through covalent bonds due to a nearby atom with higher electronegativity.
  • Higher electronegativity of nearby atoms generally leads to stronger acids.

Structure and Acidity (Size and Delocalization)

  • Larger volume over which negative charge is delocalized, the more stable the anion.
  • For halogens, the larger atomic radii of iodide allows for more delocalization, making HI stronger acid.

Lewis Acids and Bases (Definition)

  • Lewis acid: accepts a pair of electrons to form a new covalent bond.
  • Lewis base: donates a pair of electrons to form a new covalent bond.

Lewis Acids and Bases (HCl in Water Example)

  • HCl dissolves in water, donating a proton (H+) to a water molecule (Lewis base), forming a hydronium ion (H3O+).

Lewis Acids and Bases (HCl in Methanol Example)

  • HCl dissolves in methanol, donating H to CH3OH, forming an oxonium ion.

Lewis Acids and Bases (Table 2.3)

  • The table organizes some organic Lewis bases and their relative strengths in proton-transfer reactions.

Lewis Acids and Bases (Carbocations)

  • Carbocation: a carbon cation carrying a positive formal charge, bonded to only three atoms.
  • Carbocation is a Lewis acid, accepting electron pairs.

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Description

This quiz explores the definitions and properties of Arrhenius acids and bases as initially proposed by Svante Arrhenius in 1884. It delves into how these substances behave in aqueous solutions and also touches upon the Brønsted-Lowry theory. Ideal for chemistry students looking to solidify their understanding of foundational acid-base concepts.

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