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. (C)</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. (D)</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) (C)</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. (A)</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 (D)</p> Signup and view all the answers

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

<p>H2PO4^- (A)</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 (B)</p> Signup and view all the answers

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

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

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

<p>The salt of the conjugate base. (B)</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 (A)</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 (C)</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 (B)</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 (C)</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. (C)</p> Signup and view all the answers

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

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

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

<p>NH4NO3 (D)</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 (D)</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 (A)</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. (D)</p> Signup and view all the answers

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

<p>6.3 (A)</p> Signup and view all the answers

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

<p>CH3COONH4 (C)</p> Signup and view all the answers

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

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

What is a polydentate ligand?

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

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

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

What is the purpose of acid-base titration?

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

Which of the following pKa values indicates the strongest acid?

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

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

<p>Phenolphthalein (A)</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 (D)</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 (B)</p> Signup and view all the answers

What is the pKb value used to determine?

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

Which of the following acids has the highest pKa?

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

Flashcards

Hydrolysis

A chemical reaction where water participates as a reactant.

Salt

An ionic compound formed by the reaction of an acid and a base. It consists of cations and anions.

Neutral Salt

A salt formed from a strong acid and a strong base. Its aqueous solution is neutral.

Acidic Salt

A salt formed from a strong acid and a weak base. Its aqueous solution is acidic.

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Basic Salt

A salt formed from a weak acid and a strong base. Its aqueous solution is basic.

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Salt Hydrolysis

The reaction of a salt with water, resulting in the formation of hydronium ions (H3O+) or hydroxide ions (OH-), making the solution acidic or basic.

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pKa

The negative logarithm of the acid dissociation constant (Ka) of a weak acid. Higher pKa values indicate weaker acids.

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pKb

The negative logarithm of the base association constant (Kb) of a weak base. Higher pKb values indicate weaker bases.

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Titration

A technique used to determine the unknown concentration of a solution by reacting it with a solution of known concentration.

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Neutralization Reaction

A chemical reaction between an acid and a base that forms salt and water.

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Equivalence Point

The point in a titration where the moles of acid and base are equal, resulting in a neutral solution.

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Acid-base Indicator

A substance that changes color in the presence of an acid or a base, used to indicate the equivalence point in a titration.

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Titrant

A solution of known concentration used to determine the concentration of an unknown solution during titration.

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Analyte

The solution of unknown concentration that is titrated.

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Titration Curve

A graph that plots pH against the volume of titrant added, showing the change in pH during a titration.

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Universal Indicator

A combination of several indicators that shows a continuous color change over a wide pH range.

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Salts of Weak Acids & Weak Bases

Solutions containing salts of weak acids and weak bases exhibit pH values dependent on the relative strengths of the acid and base. If the acid is stronger, the solution will be acidic. If the base is stronger, the solution will be basic. If their strengths are equal, the solution will be neutral.

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Coordination Complex

A coordination complex is a molecule that contains a metal ion (Lewis acid) bonded to ligands (Lewis bases) through coordinate covalent bonds. These bonds involve a metal atom/ion accepting electron pairs from ligands.

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Coordination Number

The number of ligands directly bound to a central metal ion in a complex is known as the coordination number. This number indicates the number of coordinate bonds the metal ion forms.

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Monodental Ligand

A ligand that binds to the metal ion through one atom is called a monodental ligand. These ligands donate one electron pair to the metal ion.

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Polydentate Ligand

A polydentate ligand is a ligand that binds to the metal ion through two or more atoms. These ligands act as multiple donors of electron pairs to the metal ion.

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Chelate

A stable complex formed between a metal ion and a polydentate ligand. The ligand wraps around the metal ion, forming a ring-like structure. These complexes are generally more stable than those formed with monodental ligands.

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Hydrolysis of Metal Salts

The process of a metal ion or a metal complex reacting with water (hydrolysis) releasing H+ ions and making the solution acidic. This occurs with transition metals and some p-field metals like Al, Sn, and Pb.

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Hydrolysis of Transition Metal Ions

Transition metal ions, particularly in their hydrated forms, can react with water. This reaction often leads to the formation of a hydroxide species and the release of protons, making the solution acidic.

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What is a buffer?

A solution that resists changes in pH when small amounts of acid or base are added.

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How are buffer systems made?

A buffer system can be made of a weak acid and the salt of its conjugate base, or a weak base and the salt of its conjugate acid.

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What are the components of a buffer?

Buffers contain both acidic and basic species. The acidic component reacts with added base, while the basic component reacts with added acid.

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What is the common ion effect?

The common ion effect is a shift in equilibrium caused by the addition of a substance that already exists in the reaction. It's like adding more of one ingredient to a dish, affecting the flavors.

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How does the pH of a buffer solution change?

The pH of a buffer solution depends on the ratio of the concentrations of the acidic and basic components. This way, the buffering capacity can be adjusted by changing the concentrations.

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Buffer Solution

A mixture that resists changes in pH upon the addition of small amounts of acid or base. Typically made with a weak acid and its conjugate base, or a weak base and its conjugate acid.

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Buffer System

A solution containing a weak acid and its conjugate base, or a weak base and its conjugate acid, which can resist changes in pH.

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Buffer Capacity

The ability of a buffer solution to resist changes in pH upon the addition of acid or base.

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Henderson-Hasselbalch Equation

An equation that relates the pH of a buffer solution to the pKa of the weak acid and the ratio of the concentrations of the weak acid and its conjugate base.

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Best Buffering Range

The pH value at which a buffer system works most effectively. It is typically within ±1 pH unit of the pKa of the weak acid.

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Neutralization of HNO3 by NH3/ (NH4)2SO4 Buffer

The reaction between a weak base like ammonia (NH3) and a strong acid like HNO3, where the acid donates H+ ions to the base, forming ammonium ions (NH4+) and a salt with a neutral pH.

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Neutralization of KOH by NH3/ (NH4)2SO4 Buffer

The reaction between a strong base like KOH and the conjugate acid of a weak base, like NH4+ from NH3/ (NH4)2SO4 buffer. The base accepts H+ ions from the conjugate acid, maintaining the buffer's pH.

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Buffering action

Maintaining a stable pH around a certain point in a solution, even when adding acid or base. Buffers play a crucial role in biological systems by ensuring optimal conditions for various biochemical reactions.

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Hydrolysis in a Buffer

The process where a weak acid or base reacts with water, forming its conjugate base or acid, respectively. This process contributes to the buffer's ability to resist changes in pH.

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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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Essentials of Chemistry Topic 38-39 PDF

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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