Essentials of Chemistry - Week 10
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Questions and Answers

What is the primary function of a buffer solution?

  • To enhance the acidity of a solution.
  • To resist changes in pH upon addition of acids or bases. (correct)
  • To completely neutralize added acids or bases.
  • To change the pH rapidly.

    • Using the Henderson-Hasselbalch equation, how does the pH of a buffer relate to the concentrations of its components?

  • pH is solely dependent on the concentration of the acid.
  • The pH must always equal the concentration of the acid.
  • pH is dependent on the ratio of the base to the acid concentrations. (correct)
  • pH is directly related to the volume of the solution.

    • What does the buffer capacity measure?

  • The moles of acid or base needed to change pH by one unit in a 1 L solution. (correct)
  • The total concentration of acids and bases in the solution.
  • The volume of solution required to increase pH by two units.
  • The resistance of a buffer to changes in pH upon dilution.

    • In a buffer solution composed of CH3COOH and CH3COONa, what does the term 'pKa' represent?

    <p>The pH at which concentrations of acid and conjugate base are equal.</p> Signup and view all the answers

    For optimal buffering action, where should the pH of a buffer solution be in relation to the pKa?

    <p>Within ± 1 pH unit of the pKa.</p> Signup and view all the answers

    What is the net ionic equation for the neutralization of KOH by an NH3/(NH4)2SO4 buffer solution?

    <p>NH4^+(aq) + OH^-(aq) → NH3(aq) + H2O(l)</p> Signup and view all the answers

    In the H2CO3/HCO3- buffer system, which of the following statements is true regarding high intensity exercise?

    <p>It increases CO2 levels leading to a decrease in blood pH.</p> Signup and view all the answers

    What is the molarity of the sodium hydroxide solution needed to neutralize 15.0 mL of 0.02 M sulfuric acid solution using 12.5 mL of NaOH?

    <p>0.10 M</p> Signup and view all the answers

    Which of the following effectively neutralizes excess hydroxide ions in intracellular fluid?

    <p>H2PO4^-</p> Signup and view all the answers

    What would be the pH of a solution made by mixing equal volumes of 0.010 M nitric acid and 0.010 M calcium hydroxide?

    <p>10.0</p> Signup and view all the answers

    Which of the following pairs can effectively form a buffer solution?

    <p>CH3COOH and CH3COONa</p> Signup and view all the answers

    In a typical buffer system, which species removes added acid?

    <p>The salt of the conjugate base.</p> Signup and view all the answers

    What concept explains the shift in equilibrium position due to the addition of an ion already in the reaction?

    <p>Common ion effect</p> Signup and view all the answers

    What are the concentrations of the species involved in the buffer system CH3COOH/CH3COONa in the given example?

    <p>0.1 M and 0.1 M</p> Signup and view all the answers

    Which type of salt results in an acidic solution when dissolved in water?

    <p>Salt of a strong acid and a weak base</p> Signup and view all the answers

    What is formed when a basic salt is dissolved in water?

    <p>Hydroxide ions, resulting in a basic solution</p> Signup and view all the answers

    Which of the following statements about neutral salts is correct?

    <p>They do not affect the pH of a solution.</p> Signup and view all the answers

    In the context of salt hydrolysis, which ions indicate a neutral solution?

    <p>[H3O+] = [OH-]</p> Signup and view all the answers

    Which of the following salts is most likely to produce an acidic solution?

    <p>NH4NO3</p> Signup and view all the answers

    The dissociation of which type of salt would most likely yield a strong base in solution?

    <p>Salt of a weak acid and strong base</p> Signup and view all the answers

    Which factor primarily determines the pH of a solution formed by salt hydrolysis?

    <p>The strength of the acid and base that formed the salt</p> Signup and view all the answers

    Which of the following describes the reaction during salt hydrolysis?

    <p>Salt reacts with water to produce hydronium or hydroxide ions.</p> Signup and view all the answers

    What is the pH of a 0.1 M solution of NH4NO2?

    <p>6.3</p> Signup and view all the answers

    Which salt will produce a solution with a pH of 7.0?

    <p>CH3COONH4</p> Signup and view all the answers

    What type of ion is formed when FeSO4 dissociates in water?

    <p>[Fe(H2O)6]2+</p> Signup and view all the answers

    What is a polydentate ligand?

    <p>A ligand that bonds through two or more atoms</p> Signup and view all the answers

    What is the coordination number in a complex ion?

    <p>The total number of bonds formed with ligands</p> Signup and view all the answers

    Which of the following statements is true regarding weak acid and weak base salt solutions?

    <p>They can produce acidic, neutral, or basic solutions</p> Signup and view all the answers

    What is the effect of hydrolysis of salts of transition metals in water?

    <p>They can lead to the formation of H3O+ ions</p> Signup and view all the answers

    Which compound is known as a chelate formed by polydentate ligands?

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

    What is the purpose of acid-base titration?

    <p>To determine the concentration of an unknown solution</p> Signup and view all the answers

    At the equivalence point of a titration involving HCl and NaOH, which of the following is true?

    <p>The amount of HCl and NaOH are equal</p> Signup and view all the answers

    Which of the following pKa values indicates the strongest acid?

    <p>pKa(H3PO4) = 2.16</p> Signup and view all the answers

    Which indicator would be best suited for a strong acid-strong base titration?

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

    How much NaOH is needed to completely neutralize 25.0 mL of 0.100 M HCl?

    <p>23.9 mL</p> Signup and view all the answers

    Which of the following is a property of an acid-base indicator?

    <p>It changes color based on pH</p> Signup and view all the answers

    What is the pKb value used to determine?

    <p>The strength of a base</p> Signup and view all the answers

    Which of the following acids has the highest pKa?

    <p>HCO3-</p> Signup and view all the answers

    Study Notes

    Essentials of Chemistry - Week 10

    • Topic List: Hydrolysis of salts, Acid-base titration, Indicators, Buffers, Biologically important buffer systems

    Hydrolysis of Salts

    • Definition: Hydrolysis is any chemical reaction in which one of the reactants is water.
    • Salts: An ionic compound composed of cation(s) and anion(s).
    • Types of Salts:
      • Salt of a strong acid and a strong base (neutral)
      • Salt of a strong acid and a weak base (acidic)
      • Salt of a weak acid and a strong base (basic)
      • Salt of a weak acid and a weak base (can be neutral, acidic, or basic, depending on the relative strengths of the acid and base)
    • Aqueous Solutions of Salts: Upon dissolution, a salt dissociates into ions and the ions get hydrated. Some hydrated ions may react with water, potentially forming an acidic or basic solution.
      • If [H₃O⁺] > [OH⁻], the solution is acidic.
      • If [H₃O⁺] < [OH⁻], the solution is basic.

    Neutral Salts

    • Composition: Salts of strong acids and strong bases.
    • Aqueous Solutions: Aqueous solutions of these salts are neutral (pH = 7).
    • Example: NaCl(aq)

    Acidic Salts

    • Composition: Salts of strong acids and weak bases.
    • Aqueous Solutions: Aqueous solutions of these salts are acidic (pH < 7).
    • Example: NH₄NO₃(aq)

    Basic Salts

    • Composition: Salts of weak acids and strong bases.
    • Aqueous Solutions: Aqueous solutions of these salts are basic (pH > 7).
    • Example: CH₃COONa(aq)

    Aqueous Solutions of Salts of Weak Acids and Weak Bases

    • pH Calculation: pH values are dependent on the relative strengths of the base and acid components of the salt.
    • Examples: 0.1 M NH₄NO₃(aq), 0.1 M CH₃COONa₄(aq), 0.1 M NH₄HCO₃(aq) are presented.

    Formation of Complexes

    • Complex Ion: A metal ion with Lewis bases attached to it through coordinate covalent bonds.
    • Complex Compound: A molecule with one or more metal centers (a Lewis acid) bound to ligands (Lewis bases).
    • Ligands include atoms, ions, or molecules that donate electrons to the metal.
    • Coordination Number: The total number of bonds formed between the metal atom/ion and the ligands.
    • Monodental Ligand: Bonds to the metal through one atom on the ligand.
    • Polydental Ligand: Bonds to the metal through two or more atoms on the ligand.
    • Chelate: A stable complex formed by polydentate ligands.
    • Examples: Fe₂⁺ (aq) + 6H₂O(l) → [Fe(H₂O)₆]²⁺(aq)

    Hydrolysis of Salts of Transition Metals

    • Reaction in Aqueous Solutions: Salts of transition metals and some p-block metals (Al, Sn, Pb) hydrolyze in aqueous conditions.
    • This involves proton transfer and the formation of hydronium ions.
    • Examples: Fe(H₂O)₆²⁺(aq) and Al(NO₃)₃(aq) reactions are shown.

    Acid-Base Titration

    • Definition: A procedure to determine the amount of acid (or base) in a solution by measuring the volume of base (or acid) of known concentration that reacts completely.
    • Equipment: Buret, Graduated cylinder, pH meter, beaker.
    • Equivalence Point: The point in the titration when a stoichiometric amount of reactant has been added.
    • This is an important characteristic point on titration curves.

    Acid-Base Indicators

    • Definition: Substances that display different colours in acidic or basic solutions.
    • Examples: litmus, methyl orange, phenolphthalein. These indicators transition between coloured states as the pH of the solution they're present in change.

    Universal Indicator

    • Definition: A mixture of indicators that produces different colours over a range of pH values.
    • Useful for quickly determining the approximate solution pH.

    Buffer Systems

    • Definition: Aqueous solutions that resist large changes in pH when acid or base is added.
    • Composition: Weak acids and their conjugate bases, or weak bases and their conjugate acids.
    • Importance: Buffers are crucial for maintaining the stable pH required by living systems (e.g., human blood pH).
    • Examples: CH₃COOH(aq)/CH₃COONa(aq), NH₃(aq)/NH₄Cl(aq) are specific buffer examples provided. The common ion effect influences the behavior of buffer solutions.

    pH Calculation of Buffer Solutions

    • Henderson-Hasselbalch Equation: A useful equation for determining or calculating the pH of buffer solutions. The Henderson-Hasselbalch equation is a helpful tool given equilibrium concentrations and the acid dissociation constant of the weak acid.
    • Common Ion Effect: A shift in equilibrium when an ion involved in the equilibrium reaction is added.

    Buffer Capacity

    • Definition: Quantifies the buffer solution's resistance to changes in pH.
    • Measurement: Determined by the amount of acid or base needed to change the pH by one unit.

    Biologically Important Buffer Systems

    • Importance: Essential for maintaining stable biological conditions, such as blood pH.
    • Blood Buffer System: The H₂CO₃/HCO₃⁻ buffer system plays a crucial role in regulating blood pH.
    • Intracellular Buffer System: Intracellular buffers, such as the H₂PO₄⁻/HPO₄²⁻ system, control pH within cells.

    Example Calculations

    • Example calculations involving the neutralization of acids and bases are provided.

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    Description

    This quiz covers essential concepts in chemistry, focusing on the hydrolysis of salts, acid-base titration, indicators, and buffer systems. It also discusses biologically important buffer systems and their significance in various chemical reactions. Test your understanding of these critical topics!

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