Chemistry Acids and Water
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Questions and Answers

Which of the following best describes the behavior of a strong acid in an aqueous solution?

  • It forms a weak base.
  • It completely dissociates into ions. (correct)
  • It partially dissociates into ions.
  • It does not dissociate into ions.

Which of these acids is considered a weak acid?

  • Sulfuric acid (H2SO4).
  • Hydrochloric acid (HCl).
  • Phosphoric acid (H3PO4). (correct)
  • Nitric acid (HNO3).

What differentiates a monoprotic acid from a diprotic acid?

  • Their degree of dissociation in solution.
  • The strength of conjugate base.
  • The number of hydrogen ions produced per molecule. (correct)
  • The pH of their solutions.

Which of the following is a characteristic property of bases?

<p>Slimy feel. (B)</p> Signup and view all the answers

What is the primary function of a buffer solution?

<p>To maintain a stable pH by resisting changes upon addition of acids or bases (A)</p> Signup and view all the answers

What is the primary ion released when a base dissolves in an aqueous solution?

<p>Hydroxyl ion (OH-). (C)</p> Signup and view all the answers

How does the strength of an acid related to its tendency to ionize?

<p>Stronger acids have a greater tendency to ionize. (C)</p> Signup and view all the answers

Which of the following is NOT a critical component of a buffer solution?

<p>A strong acid and its conjugate base (A)</p> Signup and view all the answers

What is the purpose of a buffer solution?

<p>To resist changes in pH when acid or base is added. (A)</p> Signup and view all the answers

What is the ideal pH range for a buffer to function, where pKa of the weak acid is the reference?

<p>pKa ± 1 pH unit (D)</p> Signup and view all the answers

What happens when hydrogen ions are added to a buffer solution?

<p>The conjugate base reacts with hydrogen ions to form an acid (D)</p> Signup and view all the answers

Which of the following describes the equilibrium constant (Ka) for acid ionization?

<p>Ka = [H+][A-]/[HA] (B)</p> Signup and view all the answers

Which of the following is a weak base commonly used in antacids?

<p>Magnesium hydroxide (Mg(OH)2). (C)</p> Signup and view all the answers

Which of the following is an example of a buffer system?

<p>Acetic acid and acetate salt (A)</p> Signup and view all the answers

Which term refers to acids that have more than one ionizable proton per molecule?

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

Why are buffers important in biological systems?

<p>To maintain a stable pH range to support optimal enzyme activity and biological processes (D)</p> Signup and view all the answers

If a weak acid has a pKa of 6.2, what is the effective buffering range?

<p>5.2 - 7.2 (C)</p> Signup and view all the answers

Which of these options is a buffer found in physiological systems mentioned in the text?

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

Which of these best describes how to prepare a buffer solution?

<p>Use a weak acid and/or base and its conjugate form, with pKa near the intended pH (C)</p> Signup and view all the answers

What is the term for a reaction where a biomolecule is split using water?

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

What type of reaction forms a biomolecule using two components, with the elimination of water?

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

When water molecules ionize, what are the resulting ions?

<p>Hydronium and hydroxide ions (B)</p> Signup and view all the answers

What is the term for a solution with an excess of hydrogen ions?

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

What does it mean when we say water is dipolar?

<p>Its electrical charge is distributed unequally. (C)</p> Signup and view all the answers

Why is water able to dissolve large quantities of charged compounds?

<p>Because it has a strong dipole and a high dielectric constant. (D)</p> Signup and view all the answers

What kind of bonds enable water to dissolve many organic molecules with functional groups?

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

Within a water molecule, which atom is more electronegative?

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

What does an acid release in solution?

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

Flashcards

Acid

A compound that releases hydrogen ions (H+) when dissolved in water.

Acid Dissociation

A compound that dissociates in aqueous solution to produce a proton (H+) and a conjugate base (A-).

Strong Acids

Acids that ionize completely in solution.

Weak Acids

Acids that ionize partially in solution.

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Monoprotic Acid

Acids that donate only one proton per molecule.

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Diprotic Acid

Acids that donate two protons per molecule.

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Polyprotic Acid

Acids that donate more than two protons per molecule.

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Buffer

A solution that resists changes in pH when an acid or base is added.

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Base

An ionic compound that releases hydroxide ions (OH-) in solution.

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Acid Dissociation Constant (Ka)

The tendency of a conjugate acid (HA) to lose a proton and form its conjugate base (A-) is defined by the equilibrium constant (Keq) for the reversible reaction, HA  H+ + A- .

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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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What are the components of a buffer?

Buffers are typically made up of a weak acid and its conjugate base.

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What is the buffer range?

A buffer's resistance to pH change is greatest when the pH is within one unit (plus or minus) of the pKa of the weak acid.

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What are essential factors when choosing a buffer?

It's essential to select a buffer that is compatible with the experiment and won't interfere with cell functions.

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What is the phosphate buffer?

The phosphate buffer system helps maintain a stable pH in intracellular fluids and blood.

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What is the bicarbonate buffer?

The bicarbonate buffer system is crucial for regulating the pH of blood.

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What is the protein buffer?

Proteins can act as buffers due to their amino acid structure.

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How does a buffer regulate pH when an acid is added?

When hydrogen ions (H+) are added, the buffer's conjugate base can neutralize them, forming the weak acid.

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How does a buffer regulate pH when a base is added?

When hydroxide ions (OH-) are added, the buffer's weak acid reacts, forming water and the conjugate base.

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What is the biological significance of buffers?

Buffers play crucial roles in maintaining the stable pH of body fluids like blood, cerebrospinal fluid, and saliva, ensuring proper function.

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Hydrolysis

A chemical reaction where a biomolecule is broken down with the help of water.

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Condensation Reaction

A chemical reaction where two components join to form a biomolecule while releasing water.

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Water Ionization

The process where water molecule dissociates into a hydrogen ion (H+) and a hydroxide ion (OH-).

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Neutral Solution

A solution with an equal concentration of hydrogen ions (H+) and hydroxide ions (OH-).

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Proton Donor

A substance that donates hydrogen ions (H+) in a reaction.

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Proton Acceptor

A substance that accepts hydrogen ions (H+) in a reaction.

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Acid Strength

The tendency to release hydrogen ions (H+) in water.

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Study Notes

Water

  • Water is a direct participant in many biochemical reactions
  • Hydrolysis reaction: A biomolecule is split apart by water
  • Condensation reaction: A biomolecule is formed from two components with the elimination of water
  • Water has a slight tendency to ionize into hydrogen (H+) and hydroxide (OH-) ions
  • H₂O ⇌ H⁺ + OH⁻
  • Free protons (H⁺) do not exist in solution; they immediately combine with water to form hydronium ions (H₃O⁺)
  • Water can form acids and bases

Acids

  • An acid is any ionic compound that releases hydrogen ions (H⁺) in solution
  • Weak acids have a sour taste
  • Strong acids are highly corrosive
  • Examples:
    • Ascorbic acid (Vitamin C)
    • Citric acid (citrus fruits)
    • Phosphoric acid (soft drinks, rust removal)

Types of Acids

  • Strong acids dissociate completely in water
  • Weak acids dissociate partially in water
  • Monoprotic acids: release one ionizable proton (e.g., HCl)
  • Diprotic acids: release two ionizable protons (e.g., H₂SO₄)
  • Polyprotic acids: release more than two ionizable protons (e.g., H₃PO₄)

Bases

  • A base is an ionic compound that releases hydroxide ions (OH⁻) in solution
  • Bases are also called alkaline substances
  • Taste: Bitter
  • Touch: Slimy or soapy
  • Reactivity: Strong bases are caustic on organic matter; react violently with acids
  • Examples:
    • Sodium hydroxide (lye, oven cleaners)
    • Magnesium hydroxide (milk of magnesia, antacids, laxatives)

Dissociation Constants of Weak Acids and Bases

  • Weak acids and bases do not completely ionize in water; the extent of ionization depends on pH
  • Equilibrium constant (Ka) for a weak acid's ionization is called the acid dissociation constant

Buffers

  • Definition: A solution that resists changes in pH when acid or base is added
  • Components: A weak acid and its conjugate base (e.g., acetic acid and acetate, carbonic acid and bicarbonate)

Why Use Buffers?

  • Enzyme reactions and cell functions have optimal pH ranges
  • Maintain the structure and/or activity of biological materials

Factors in Choosing a Buffer

  • The buffer should cover the desired pH range (generally ±1 pH unit from the pKa value of the weak acid)
  • The buffer should not be toxic to the cells or organisms being studied
  • The buffer should not interfere with the experiment

Buffers of Physiological Importance

  • Phosphate buffer
  • Bicarbonate buffer
  • Protein buffer

How Buffers Regulate pH

  • If hydrogen ions are added, the conjugate base reacts with them, forming the acid
  • If hydroxide ions are added, the acid reacts with them, forming water and the conjugate base

Biological Importance of Buffer

  • Body fluids (blood, cerebrospinal fluid, saliva) maintain a constant pH range
  • Buffering is essential because hydrogen and hydroxyl ions are constantly produced by metabolism

Preparation of Buffer

  • Buffers resist pH changes if the pH is near the pKa value of the weak acid
  • Buffer range: ±1 pH unit from the pKa value

The Henderson-Hasselbalch Equation

  • Describes the shape of titration curves for weak acids
  • pH = pKa + log([conjugate base]/[acid])

Worked Example

  • Calculating pH of a mixture of NaH₂PO₄ and Na₂HPO₄
  • Calculating pH change when NaOH is added to a buffer solution

Additional Notes

  • This study guide covers the slides provided in the image.

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Acids Bases pH PDF

Description

Explore the fundamental concepts of water and acids through this engaging quiz. Learn about the biochemical roles of water, hydrolysis, condensation reactions, and the classification of different types of acids. Test your knowledge on how acids function in various solutions and their characteristics!

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