Study support for Acids and Bases (16:38min)

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Questions and Answers

What is the hydrogen ion concentration, [H+], of a solution with a pH of 3?

  • 1 x 10^-3 M (correct)
  • 3 x 10^-14 M
  • 3 M
  • 1 x 10^3 M

Which of these statements is correct regarding a strong acid?

  • It has a pH value that will always be 7.
  • It dissociates minimally in water.
  • It has a high pKa value.
  • It dissociates completely in water. (correct)

What happens to the pH of pure water if the temperature is decreased?

  • The pH will stay exactly at 7.
  • The pH increases making it more basic. (correct)
  • The pH decreases making it more acidic.
  • The pH will approach 0.

What is the hydroxide ion concentration, [OH-], if the hydrogen ion concentration is 1 x 10^-2 M in an aqueous solution at 25°C?

<p>1 x 10^-12 M (A)</p> Signup and view all the answers

A weak acid is titrated with a strong base, what does the pH at the equivalence point look like?

<p>pH &gt; 7 (A)</p> Signup and view all the answers

A buffer solution contains a weak acid and its conjugate base, at pH 6. If the pKa of the weak acid is 5, then what can be inferred?

<p>There is excess conjugate base. (C)</p> Signup and view all the answers

Which of these conditions gives the greatest buffering capacity?

<p>Equal concentrations of weak acid and conjugate base. (B)</p> Signup and view all the answers

How does the electronegativity of an atom bonded to the acidic hydrogen on an acid affect its acid strength?

<p>More electronegative atoms increase acidity. (C)</p> Signup and view all the answers

What occurs when a strong acid is combined with a strong base?

<p>Water is formed and the pH is neutral. (D)</p> Signup and view all the answers

How does the pH of a buffer solution change when small amounts of a strong acid are added?

<p>The pH remains relatively stable. (A)</p> Signup and view all the answers

What defines a weak acid based on its dissociation in solution?

<p>It partially ionizes. (B)</p> Signup and view all the answers

What effect does increasing temperature have on the pH of water?

<p>pH decreases, making it more acidic. (B)</p> Signup and view all the answers

Which statement is true regarding the equivalence point in a titration involving a weak acid and a strong base?

<p>The pH at the equivalence point is above 7. (A)</p> Signup and view all the answers

Which of the following equations correctly represents the relationship between pH and pKa in a buffer solution?

<p>pH = pKa + log([A-]/[HA]) (D)</p> Signup and view all the answers

How does the ratio of conjugate base to weak acid affect a buffer's capacity?

<p>Higher ratios increase buffering capacity against acids. (B)</p> Signup and view all the answers

Which of the following is a characteristic of strong acids and bases?

<p>They dissociate completely in solution. (A)</p> Signup and view all the answers

Which factors contribute to the strength of an acid?

<p>Electronegativity and stability of the conjugate base. (A)</p> Signup and view all the answers

The pH of pure water is 6 at 25°C.

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

A strong acid will completely dissociate in solution.

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

The pKa of a weak acid is directly proportional to its acidity strength.

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

In a titration of a weak acid with a strong base, the equivalence point occurs at pH 7.

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

Increasing temperature will cause the pH of a solution to decrease.

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

Buffers can only consist of strong acids and strong bases.

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

The Henderson-Hasselbalch equation can be used to calculate the pH of a buffer solution.

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

All strong bases are derived from Group 1 and Group 2 hydroxides.

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

Match the following terms with their corresponding definitions:

<p>pH = a measure of hydrogen ion concentration pOH = a measure of hydroxide ion concentration pKa = a measure of acid dissociation Kw = the ion-product constant for water</p> Signup and view all the answers

Match the acid/base type with their reaction characteristics,

<p>Strong acid + strong base = Neutralization to form water Weak acid + strong base = Forms water and conjugate base Weak base + strong acid = Forms conjugate acid Weak acid + weak base = Forms conjugate base and conjugate acid</p> Signup and view all the answers

Match the following scenarios with the corresponding pH shifts during acid-base titration:

<p>Strong acid - strong base titration = Equivalence point at pH 7 Weak acid - strong base titration = Equivalence point above pH 7 Weak base - strong acid titration = Equivalence point below pH 7 Halfway to equivalence point of weak acid = pH equals pKa</p> Signup and view all the answers

Match the following properties of acids or bases with their characteristics:

<p>Stronger acid = Higher Ka value Stronger acid/weaker base = More electronegative atom bonded to acidic H Stronger base = Less electronegative atom bonded to acidic H Stronger buffer = Greater concentration of weak acid and conjugate base</p> Signup and view all the answers

Match the conditions with their relation to pH in a buffer system:

<p>pH = pKa = Equal concentrations of weak acid and conjugate base pH &gt; pKa = More conjugate base than weak acid pH &lt; pKa = More weak acid than conjugate base Buffering capacity maximum = Equal concentrations of weak acid and conjugate base</p> Signup and view all the answers

Match the following concepts in acid-base chemistry with their description:

<p>Dissociation = Separation of molecules into ions Equilibrium = Rate of forward reaction equals the rate of reverse reaction Titration = Process to determine the concentration of unknown solution with solution with known concentraton Buffering Capacity = Ability of a solution to resist pH changes</p> Signup and view all the answers

Match the following mathematical expressions with their application in solution chemistry:

<p>pH = -log[H+] = Calculating pH from hydrogen ion concentration pOH = -log[OH-] = Calculating pOH from hydroxide ion concentration Kw = [H+][OH-] = Ion-product constant for water pH = pKa + log([A-]/[HA]) = Henderson-Hasselbalch equation</p> Signup and view all the answers

Match the terms with their relevance in acid-base chemistry:

<p>Strong acids = Completely dissociate in solution Weak acids = Partially dissociate in solution Buffer solutions = Resist changes in pH upon addition of acid or base Equivalence point = Stoichiometrically equal amount of titrant and analyte are present</p> Signup and view all the answers

Flashcards

pH

The negative logarithm of the hydrogen ion concentration ([H+]) in a solution. It measures the acidity or alkalinity of a solution.

pOH

The negative logarithm of the hydroxide ion concentration ([OH-]) in a solution. It is related to pH by the equation: pH + pOH = 14.

Kw (ionic product of water)

The equilibrium constant for the autoionization of water. It represents the product of hydrogen ion and hydroxide ion concentrations. At 25°C, Kw = 1 × 10^-14.

Strong Acid

An acid that dissociates 100% in solution, releasing all its hydrogen ions (H+). They are strong electrolytes, conducting electricity well.

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Strong Base

A base that dissociates 100% in solution, releasing all its hydroxide ions (OH-). They are strong electrolytes, conducting electricity well.

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Weak Acid

An acid that only partially dissociates in solution, releasing a small amount of hydrogen ions (H+). They are weak electrolytes.

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Weak Base

A base that only partially dissociates in solution, accepting a small amount of hydrogen ions (H+). They are weak electrolytes.

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Ka (acid dissociation constant)

The equilibrium constant for the dissociation of a weak acid. It indicates the strength of the acid: smaller Ka values indicate weaker acids.

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Buffer Solution

A solution that contains significant concentrations of a weak acid and its conjugate base. It resists changes in pH when small amounts of acid or base are added.

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Equivalence Point

The point in a titration where the moles of acid and base are equal. It marks the complete neutralization of the analyte by the titrant.

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Strong Acids and Bases

Strong acids and bases completely ionize in solution, releasing all their H+ or OH- ions. For example, HCl and NaOH are strong acid and base.

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Acid-Base Titration

The process of gradually adding a solution of known concentration (titrant) to a solution of unknown concentration (analyte) to determine the unknown concentration. It's used to find the concentration of an unknown solution by carefully adding a solution of known concentration, reacting the two.

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Weak Acids and Bases

Weak acids and bases only partially ionize in solution, releasing only a small amount of H+ or OH- ions. For example, acetic acid (CH3COOH) is a weak acid.

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Henderson-Hasselbalch Equation

The relationship between pH, pKa, and the concentrations of a weak acid (HA) and its conjugate base (A-). It helps predict the pH of a buffer solution.

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What is pH?

The negative logarithm of the hydrogen ion concentration ([H+]) in a solution. It measures the acidity or alkalinity of a solution.

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What is pOH?

The negative logarithm of the hydroxide ion concentration ([OH-]) in a solution. It is related to pH by the equation: pH + pOH = 14.

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What is Kw?

The equilibrium constant for the autoionization of water. It represents the product of hydrogen ion and hydroxide ion concentrations. At 25°C, Kw = 1 × 10^-14.

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What is a strong acid?

An acid that dissociates 100% in solution, releasing all its hydrogen ions (H+). They are strong electrolytes, conducting electricity well.

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What is a strong base?

A base that dissociates 100% in solution, releasing all its hydroxide ions (OH-). They are strong electrolytes, conducting electricity well.

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What is a weak acid?

An acid that only partially dissociates in solution, releasing a small amount of hydrogen ions (H+). They are weak electrolytes.

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What is a weak base?

A base that only partially dissociates in solution, accepting a small amount of hydrogen ions (H+). They are weak electrolytes.

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What is Ka?

The equilibrium constant for the dissociation of a weak acid. It indicates the strength of the acid: smaller Ka values indicate weaker acids.

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Study Notes

Introduction to Acids and Bases

  • pH = -log[H+]; pOH = -log[OH-]
  • Kw = [H+][OH-] = 1 x 10-14 at 25°C
  • Pure water has a pH of 7, pOH of 7, and Kw of 1 x 10-14
  • Temperature affects pH:
    • Above 25°C, pH decreases (more acidic)
    • Below 25°C, pH increases (more basic)

Strong Acids and Bases

  • Strong acids and bases dissociate 100% in solution.
  • Strong acids and bases are strong electrolytes and conduct electricity well.
  • Strong acid examples: HCl, HBr, HI, H2SO4, HNO3, HClO4
  • Strong base examples: Group 1 hydroxides (LiOH, NaOH, KOH) and Group 2 hydroxides (Ba(OH)2, Sr(OH)2)
  • Calculate pH/pOH for strong acids/bases using pH = -log[H+] and pOH = -log[OH-]. pOH + pH = 14

Weak Acids and Bases and Equilibria

  • Weak acids and bases dissociate only partially in solution.
  • Use Ka or Kb values to determine the strength of a weak acid or base.
  • Ka = [H+][A-]/[HA] (equilibrium constant for weak acid dissociation)
  • pKa = -log Ka
  • Use ICE tables and the Ka or Kb expression to solve equilibrium concentrations.
  • Acids donate protons (H+). Bases accept protons.
  • Example: HCN (weak acid) in water: HCN + H2O ↔ H3O+ + CN-. Knowing the Ka value, you can calculate the pH of the solution.

Acid-Base Reactions and Buffers

  • Strong acid + strong base: H+ + OH- → H2O
  • Weak acid + strong base: HA + OH- → H2O + A-
  • Weak base + strong acid: B + H+ → BH+
  • Weak acid + weak base: HA + B → A- + BH+
  • Buffers are solutions containing significant concentrations of a weak acid and its conjugate base; they stabilize pH and react with added strong acids or bases to minimize pH change.

Acid-Base Titrations

  • Titration involves gradually adding a solution of known concentration to a solution of unknown concentration.
  • Equivalence point: The point where moles of acid and base are equal.
  • Strong acid-strong base titration: Equivalence point at pH = 7
  • Weak acid-strong base titration: Equivalence point at pH > 7
  • Weak base-strong acid titration: Equivalence point at pH < 7
  • Halfway to the equivalence point, pH = pKa.

Molecular Structure and Acid/Base Strength

  • Stronger acids have higher Ka values.
  • Electronegativity impacts acid strength: More electronegative elements stabilize the conjugate base, making the acid stronger.
  • Stronger acids form weaker conjugate bases.
  • Stronger bases form weaker conjugate acids.

pH and pKa

  • pH > pKa: more conjugate base than weak acid
  • pH < pKa: more weak acid than conjugate base
  • Buffer solution: contains a weak acid and its conjugate base.
    • pH is higher than pKa: more conjugate base
    • pH is lower than pKa: more weak acid

Properties of Buffers

  • Buffering capacity:
    • Ability to resist pH changes.
    • Higher buffering capacity with greater concentrations of weak acid and conjugate base.
    • Highest buffering capacity when concentrations of weak acid and conjugate base are approximately equal.
  • Buffers have higher buffering capacity against acids if the buffer has more conjugate base, and vice versa.

Henderson-Hasselbalch Equation

  • pH = pKa + log([A-]/[HA])
  • Calculates pH of a buffer solution.
  • In a perfect buffer ([A-] = [HA]), pH = pKa.

Buffering Capacity

  • Buffering capacity can be affected by changes in concentration of the weak acid or conjugate base.
  • Impurities in buffer components can alter pH.
  • Buffering capacity against acids is greater with more conjugate base.
  • Buffering capacity against bases is greater with more weak acid.

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