Acids and Bases

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Questions and Answers

How does the Brønsted-Lowry definition of acids and bases differ fundamentally from earlier definitions?

  • It focuses solely on the production of hydroxide ions in aqueous solutions.
  • It introduces the concept of pH as a measure of acidity and basicity.
  • It restricts the definition to only include strong acids and bases.
  • It broadens the definition to include substances that can donate or accept protons, not just those affecting hydroxide ion concentration. (correct)

Ammonia (NH3) is considered a base even though it does not contain OH- ions in its formula. What mechanism allows it to act as a base?

  • Ammonia donates protons to water molecules, increasing hydronium ion concentration.
  • Ammonia acts as a strong acid, neutralizing any bases present.
  • Ammonia directly releases hydroxide ions into a solution.
  • Ammonia undergoes hydrolysis, reacting with water to generate hydroxide ions. (correct)

What property defines a substance as amphiprotic?

  • The ability to act only as a proton acceptor.
  • The ability to neutralize both strong acids and strong bases simultaneously.
  • The ability to act as either a proton donor or a proton acceptor. (correct)
  • The ability to act only as a proton donor.

A scientist discovers a new compound and finds that its aqueous solution has a pH of 9. Based on this information, how would you classify the compound?

<p>Basic, because it increases the concentration of hydroxide ions. (B)</p> Signup and view all the answers

Given the equation for pH, $pH = -log[H_3O^+]$, how does a tenfold increase in the hydronium ion concentration, $[H_3O^+]$, affect the pH of a solution?

<p>It decreases the pH by one unit. (A)</p> Signup and view all the answers

At room temperature, the self-ionization of water is described by the equation $Kw = [H_3O^+][OH^-] = 1.0 imes 10^{-14}$. If a solution has a hydronium ion concentration of $1.0 imes 10^{-5}$ M, what is the hydroxide ion concentration, and what is the pH?

<p>$[OH^-] = 1.0 imes 10^{-9}$ M, pH = 5 (D)</p> Signup and view all the answers

How does the behavior of strong acids and bases in aqueous solutions differ from that of weak acids and bases?

<p>Strong acids and bases completely dissociate, while weak acids and bases only partially dissociate. (D)</p> Signup and view all the answers

For a weak acid, the acid dissociation constant, $K_a$, is defined as $K_a = rac{([H_3O^+][A^-])}{[HA]}$. What does a smaller $K_a$ value indicate about the strength of the acid?

<p>The acid is weak and only slightly dissociates in water. (C)</p> Signup and view all the answers

A buffer solution is prepared to maintain a stable pH. What is the primary mechanism by which a buffer resists changes in pH upon the addition of small amounts of acid or base?

<p>By shifting the equilibrium to consume the added acid or base. (B)</p> Signup and view all the answers

The buffer capacity is defined as the amount of acid or base that can be added before the pH begins to change significantly. How is buffer capacity quantitatively defined?

<p>The quantity of strong acid or base needed to change the pH of one liter of solution by one pH unit. (B)</p> Signup and view all the answers

How would the Arrhenius definition classify $CH_3COOH$ in an aqueous solution?

<p>As an acid because it increases the hydrogen ion ($H^+$) concentration. (D)</p> Signup and view all the answers

Which statement correctly describes the roles of Johannes Bronsted and Thomas Lowry in defining acids and bases?

<p>They independently redefined acids as proton donors and bases as proton acceptors, focusing on proton transfer. (C)</p> Signup and view all the answers

In a chemical reaction, water can act as both a proton donor and a proton acceptor. What term describes substances with this dual capability?

<p>Amphoteric (C)</p> Signup and view all the answers

What approach did Soren Sorensen introduce in 1909 to quantify acidity and basicity in aqueous solutions more conveniently?

<p>The pH scale, which uses a logarithmic scale to represent hydrogen ion concentration. (B)</p> Signup and view all the answers

Given $pKw = pH + pOH = 14$ at room temperature, if a solution has a $pH$ of 6.0, what is its $pOH$ and how does this relate to its acidity or basicity?

<p>$pOH = 8.0$, making the solution acidic. (C)</p> Signup and view all the answers

How does calculating the hydronium ion concentration in a strong acid solution differ from that of a weak acid solution?

<p>In strong acids, it is calculated directly from the molar concentration of the acid, assuming complete dissociation. (C)</p> Signup and view all the answers

For a weak base, the base dissociation constant, $K_b$, is represented as $Kb = rac{([OH^-][B^+])}{[B]}$. What does this constant indicate about the strength of the weak base?

<p>The base is weak and only partially dissociates, meaning that most of the base remains un-ionized. (C)</p> Signup and view all the answers

How does adding a strong acid to a buffer solution affect the equilibrium and what components of the buffer system counteract this addition?

<p>It shifts the equilibrium to remove the added acid, reacting with the conjugate base in the buffer system. (B)</p> Signup and view all the answers

A laboratory technician prepares a buffer solution for an experiment but finds that adding only a small amount of acid causes a significant pH change. What is the most likely reason for this?

<p>The buffer components were already fully reacted or saturated. (A)</p> Signup and view all the answers

Why is the concept of buffer capacity important in biological systems, such as blood, and what happens if the buffer capacity is exceeded?

<p>It helps maintain stable pH levels necessary for enzymatic activity and cellular function; exceeding it can lead to metabolic acidosis or alkalosis. (D)</p> Signup and view all the answers

Flashcards

Bronsted-Lowry Acid

In the Bronsted-Lowry definition, it donates protons.

Bronsted-Lowry Base

In the Bronsted-Lowry definition, it accepts protons.

Arrhenius Acid

Arrhenius acid is a compound that increases the H+ ion concentration in an aqueous solution.

Arrhenius Base

Arrhenius base is a compound that increases the OH- ion concentration in an aqueous solution.

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Ammonia (NH3) as a Base

It generates OH- ions via a proton-transfer reaction with H2O molecules.

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Amphiprotic Substance

A substance that can act as both a proton donor (PD) and a proton acceptor (PA).

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pH Testing

A measure if a solution is acidic or basic.

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Neutral pH

A pH of 7

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Acidic pH

A pH of less than 7

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Basic pH

A pH greater than 7.

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pH Equation

pH= -log(H3O+)

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Self-ionization of water

Kw = (H3O+)(OH-) = 1.0 x 10^-14

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pKw equation

pKw= pH + pOH = 14

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Strong Acid

In an aqueous solution of a strong acid, it's the main source of hydronium ions.

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Strong Base

In an aqueous solution of a strong base, it's the main source of hydroxide ions.

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Weak Acids

Weak acids only partially dissociate in aqueous solutions and reach a condition of equilibrium. Ka = (H3O+) (A-)/HA

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Weak Bases

Weak bases only partially dissociate in aqueous solutions and reach a condition of equilibrium. Kb = (OH-) (B+)/B

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Buffer

Stops massive changes in pH levels.

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Buffer Capacity

The amount of acid or base that can be added before the pH begins to change significantly.

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Study Notes

  • Acids and Bases are fundamental concepts in chemistry.

Bronsted-Lowry Definition

  • In 1923, Johannes Bronsted and Thomas Lowry independently defined acids and bases based on proton transfer.
  • An acid is a proton donor (PD).
  • A base is a proton acceptor (PA).

Arrhenius Definition

  • An Arrhenius acid increases the H+ ion concentration in an aqueous solution.
  • An Arrhenius base increases the OH- ion concentration in an aqueous solution.

Ammonia as a Base

  • Ammonia (NH3) is a base that does not contain OH- ions in its formula.
  • Ammonia generates OH- ions through a proton-transfer reaction with H2O molecules.
  • The reaction of ammonia with water is called hydrolysis.

Amphiprotic Substances

  • H2O can act as both a proton donor and a proton acceptor, depending on the chemical reaction.
  • A substance that can act as a PD or a PA is called amphiprotic.

pH Testing

  • pH testing, or potential of hydrogen ion, is used to test if a substance is acidic or basic.
  • Soren Sorensen, a Danish biochemist, proposed pH testing in 1909 to conveniently describe hydronium and hydroxide ion concentrations in aqueous solutions.
  • The pH scale ranges from 0 to 14 in water.
  • A pH of 7 is considered neutral.
  • A pH less than 7 is considered acidic.
  • A pH greater than 7 is considered basic.
  • The equation to determine the pH of an aqueous solution is pH= -log(H3O+).

Self-ionization of Water

  • At room temperature, Kw = (H3O+)(OH-) = 1.0 x 10-14.
  • pKw = pH + pOH = 14.

Strong Acids and Bases

  • When calculating hydronium concentration in a strong acid, the strong acid is the main source of hydronium ions.
  • When calculating hydroxide concentration in a strong base, the strong base is the main source of hydroxide ions.

Weak Acids and Bases

  • Weak acids only partially dissociate in aqueous solutions and reach a condition of equilibrium.
  • Ka = (H3O+)(A-)/HA
  • Weak bases only partially dissociate in aqueous solutions and reach a condition of equilibrium.
  • Kb = (OH-)(B+)/B

Buffers

  • A buffer is a special solution that stops massive changes in pH levels.
  • Every buffer has a certain buffer capacity and buffer range.
  • Buffer capacity is the amount of acid or base that can be added before the pH begins to change significantly.
  • Buffer capacity can also be defined as the quantity of strong acid or base needed to change the pH of one liter of solution by one pH unit.

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