Acid-Base Chemistry Quiz
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Questions and Answers

What does the term 'concentration' specifically refer to in a solution?

  • The temperature of the solution
  • The number of solute particles in a given volume (correct)
  • The total mass of solute in the solution
  • The strength of the acid or base present

Which of the following accurately describes electrolytes?

  • They are solely acids and bases
  • They absorb electricity when dissolved
  • They dissociate into ions in solution (correct)
  • They do not conduct electricity in solution

What is the pH of a neutral solution at 25°C?

  • 7 (correct)
  • 10
  • 0
  • 14

What is the expression that represents the ionic product of water (Kw)?

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

How does the self-ionisation of water affect its classification as an electrolyte?

<p>Because it forms very few ions (D)</p> Signup and view all the answers

How is pH defined mathematically?

<p>pH = -log10[H3O+] (A)</p> Signup and view all the answers

What happens to the value of Kw as temperature increases?

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

At 25°C, what is the concentration of hydroxide ions ([OH-]) in pure water?

<p>$10^{-7}$ mol L-1 (D)</p> Signup and view all the answers

What is the relationship between pH and pOH at 25°C?

<p>pH + pOH = 14 (C)</p> Signup and view all the answers

Which of the following substances can act as both an acid and a base?

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

What happens to pH when an acid is added to a buffer solution?

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

What is a primary function of buffers in biological systems?

<p>To maintain pH stability (A)</p> Signup and view all the answers

Which reaction represents how acetic acid in a buffer neutralizes added hydroxide ions?

<p>HC2H3O2(aq) + OH−(aq) → C2H3O2−(aq) + H2O(l) (D)</p> Signup and view all the answers

What is required for a substance to be considered amphoteric?

<p>It must have an ‘H’ to donate and a free electron pair to accept (A)</p> Signup and view all the answers

Why do buffers have equal concentrations of a weak acid and its salt?

<p>To effectively resist pH changes (B)</p> Signup and view all the answers

What would occur to blood pH if there is a significant surplus of H3O+ ions?

<p>Blood pH would decrease (C)</p> Signup and view all the answers

What can be inferred about nitrous acid compared to ethanoic acid?

<p>Nitrous acid is a stronger weak acid than ethanoic acid. (D)</p> Signup and view all the answers

How many dissociation constants does oxalic acid have?

<p>Two, as it is a diprotic acid. (A)</p> Signup and view all the answers

Which of the following correctly describes a strong base?

<p>It completely dissociates into metal ions and hydroxide ions in solution. (A)</p> Signup and view all the answers

What is essential to calculate the acid dissociation constant (Ka) of a weak acid?

<p>The initial molar concentration of the acid and [H+] at equilibrium. (D)</p> Signup and view all the answers

What does the base dissociation constant (Kb) represent?

<p>The ratio of the concentration of the conjugate acid times the concentration of hydroxide ions to the concentration of the base. (A)</p> Signup and view all the answers

What is true about the extent of a reaction at equilibrium?

<p>It shows how much product is formed at equilibrium. (B)</p> Signup and view all the answers

According to Le Chatelier’s Principle, what happens when more reactant is added to an equilibrium system?

<p>The equilibrium shifts to produce more products. (C)</p> Signup and view all the answers

What happens to the concentration of NH4+ when ammonia dissolves in water?

<p>It is present in very low amounts (B)</p> Signup and view all the answers

How does increasing pressure affect a gaseous equilibrium system?

<p>It favors the direction that has fewer gas molecules. (A)</p> Signup and view all the answers

What is the relationship between Ka and Kb for a conjugate acid-base pair?

<p>Ka × Kb = Kw (C)</p> Signup and view all the answers

What role does a catalyst play in an equilibrium reaction?

<p>It speeds up the time taken to reach equilibrium without changing it. (D)</p> Signup and view all the answers

When does the equilibrium constant (Keq) not change?

<p>When an inert gas is added to the system. (A)</p> Signup and view all the answers

How is pKa related to ionization in water?

<p>Lower pKa values indicate greater ionization (C)</p> Signup and view all the answers

What does the equilibrium constant expression for the reaction aA + bB ⇌ cC + dD look like?

<p>Keq = [C]^c[D]^d/[A]^a[B]^b (A)</p> Signup and view all the answers

What is the endpoint in a titration?

<p>When the indicator changes colour (C)</p> Signup and view all the answers

What determines when an indicator changes colour in relation to pH?

<p>The concentration of acid HIn equals that of its conjugate base In- (C)</p> Signup and view all the answers

What is the effect of cooling an exothermic reaction on its equilibrium?

<p>It shifts the equilibrium toward the products. (D)</p> Signup and view all the answers

For an equilibrium system represented by 2SO2(g) + O2(g) ⇌ 2SO3(g), what happens to the ratio at equilibrium?

<p>It becomes constant regardless of initial concentrations. (A)</p> Signup and view all the answers

Why is it important to select an appropriate indicator for titrations?

<p>Indicators must change colour at the equivalence point (D)</p> Signup and view all the answers

What characterizes the dissociation of weak bases like ammonia?

<p>They only dissociate slightly in water (C)</p> Signup and view all the answers

What can be inferred if the reaction quotient (QC) is greater than the equilibrium constant (KC)?

<p>The reaction will proceed to the left. (C)</p> Signup and view all the answers

What occurs during the titration setup?

<p>The titrant is known and added to a known volume of the analyte (B)</p> Signup and view all the answers

Which type of equilibrium constant, Kb, is associated with weak bases?

<p>Concentration of products at equilibrium. (D)</p> Signup and view all the answers

What happens to the equilibrium constant (Keq) for an exothermic reaction if the temperature is increased?

<p>It decreases. (D)</p> Signup and view all the answers

How does dilution affect an equilibrium system in solution?

<p>It shifts the equilibrium to increase particles. (D)</p> Signup and view all the answers

Which factor does not affect the equilibrium constant?

<p>Addition of a catalyst. (D)</p> Signup and view all the answers

If the reaction quotient (QC) is equal to the equilibrium constant (KC), what is concluded?

<p>The system is at equilibrium. (D)</p> Signup and view all the answers

What occurs at the endpoint of a titration?

<p>The indicator changes color. (C)</p> Signup and view all the answers

In a titration curve, what does the half-equivalence point indicate?

<p>The volume of titrant added is half of the total required. (B)</p> Signup and view all the answers

How is a standard solution prepared?

<p>By dissolving a primary standard in a measured volume of water. (C)</p> Signup and view all the answers

Which statement about the pH at the half-equivalence point is correct?

<p>It is equal to the pKa of the acid. (A)</p> Signup and view all the answers

What is a common characteristic of a titration curve for a weak acid with a weak base?

<p>Gradual pH change with no sharp increase. (B)</p> Signup and view all the answers

Which of the following describes a primary standard?

<p>A pure substance used to prepare standard solutions. (B)</p> Signup and view all the answers

What is the general equation for a neutralization reaction?

<p>Acid + Base → Salt + Water (D)</p> Signup and view all the answers

What is indicated by the pH at the equivalence point in a titration?

<p>It can vary based on the strengths of acid and base. (B)</p> Signup and view all the answers

Flashcards

Electrolyte

A substance that dissolves in water to produce ions, allowing it to conduct electricity.

Concentration

The concentration of a substance in a solution, specifically the number of moles of solute per liter of solution.

Strength of an acid or base

The measure of how readily a substance ionizes in a solution.

Self-ionization of water

The equilibrium expression representing the self-ionization of water, where water molecules react to form hydronium ions (H3O+) and hydroxide ions (OH-).

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Ionic Product of Water (Kw)

The product of the concentrations of hydronium and hydroxide ions in water, constant at a specific temperature.

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pH

The negative logarithm (base 10) of the hydronium ion concentration ([H3O+]) in a solution. It measures acidity.

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Strength of an electrolyte

The extent to which a substance ionizes in solution. Strong acids/bases ionize completely; weak ones ionize partially.

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Effect of temperature on Kw

The value of Kw increases as temperature increases, meaning the self-ionization of water is enhanced at higher temperatures.

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Acid Dissociation Constant (Ka)

A measure of the strength of a weak acid, indicating how readily it donates a proton (H+) in solution. A higher Ka value signifies a stronger acid, meaning it ionizes more extensively in water.

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Stronger Weak Acid

A weak acid that ionizes more extensively in solution than another weak acid. For instance, nitrous acid is stronger than ethanoic acid as it produces a higher concentration of H+ ions in solution.

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Polyprotic Acid or Base

A weak acid or base that can donate or accept more than one proton (H+) or hydroxide ion (OH-), respectively. For instance, oxalic acid is diprotic as it donates two protons.

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Monoprotic Acid

An acid that only donates one proton (H+) per molecule.

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Base Dissociation Constant (Kb)

The ratio of the concentration of the conjugate acid multiplied by the concentration of hydroxide ions to the concentration of the base in solution. This is a measure of the strength of a weak base.

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Dynamic Equilibrium

A state where the rates of the forward and reverse reactions are equal, resulting in no net change in the concentrations of reactants and products.

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Extent of Reaction

A measure of how far a reversible reaction has progressed towards completion at equilibrium. It indicates the relative amounts of reactants and products at equilibrium.

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Le Chatelier's Principle

A principle that states that if a change in conditions is applied to a system at equilibrium, the system will shift in a direction that relieves the stress.

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Concentration Change (Stress)

A change in the concentration of reactants or products.

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Effect of Concentration Change on Equilibrium

Adding more product causes the reaction to shift towards the formation of reactants, while removing product encourages the reaction to favor product formation.

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Pressure Change (Stress)

Changes in pressure only affect gaseous equilibria. Increasing pressure favors the side with fewer gas molecules.

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Effect of Adding Inert Gas on Equilibrium

Adding an inert gas does not affect the equilibrium position, as the concentration of reactants and products remains unchanged.

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Effect of Dilution on Equilibrium (Solution)

Dilution lowers the concentration of particles, causing the equilibrium to shift towards the side with more particles.

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Temperature Change (Stress)

Increasing the temperature shifts the equilibrium position towards the endothermic direction (heat absorption).

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Catalyst

A substance that speeds up a reaction without being consumed. Catalysts lower the activation energy of both forward and reverse reactions equally, thus accelerating the attainment of equilibrium but not changing its position.

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Equilibrium Constant (Keq)

A numerical value that describes the ratio of product concentrations to reactant concentrations at equilibrium. It is a constant at a specific temperature.

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Equilibrium Constant Expression

The mathematical expression that relates the concentrations of reactants and products at equilibrium to the equilibrium constant. It includes the stoichiometric coefficients of the balanced chemical equation.

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Reaction Quotient (Qc)

A measure of the relative amounts of reactants and products at any time during a reaction. It can be used to predict the direction of a reaction based on its comparison to the equilibrium constant.

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Effect of Temperature on Equilibrium Constant

A measure of the effect of temperature on the equilibrium constant. For exothermic reactions, increasing temperature favors the reactant side, resulting in a decrease in K.

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What is pOH?

The negative logarithm of the hydroxide ion concentration ([OH-]) in a solution. It is a measure of the concentration of hydroxide ions, with a lower pOH indicating a higher concentration of hydroxide ions.

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What is an amphoteric substance?

A substance that can act as either an acid or a base, depending on the reaction conditions.

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What is a buffer solution?

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

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How is the pH of a buffer determined?

The pH of a buffer solution is determined by the relative concentrations of the weak acid and its conjugate base. The Henderson-Hasselbalch equation can be used to calculate the pH of a buffer.

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How do buffers work?

Buffers work by reacting with added acids or bases to minimize changes in pH.

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What happens when a base is added to a buffer?

In a buffer solution, the weak acid neutralizes added hydroxide ions (OH-) by donating a proton (H+), forming the conjugate base and water.

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What is the role of the salt in a buffer solution?

The salt of a weak acid and its conjugate base is added to create a buffer solution. This provides a higher concentration of the conjugate base, helping to maintain the desired pH.

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Why is the combination of a weak acid and its conjugate base important for a buffer?

The presence of both the weak acid and its conjugate base in a buffer solution ensures that the pH does not change significantly when small amounts of acid or base are added.

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Relationship between Ka and Kb

The product of Ka of an acid and Kb of its conjugate base equals Kw, the ion product of water, which is 1.0 x 10^-14 at 25°C.

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Acid-Base Indicator

A weak acid that changes color in solution depending on the pH. These indicators are used to signal the endpoint of titrations.

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Endpoint

The endpoint in a titration, where the indicator changes color, ideally matches the point at which the acid and base have neutralized each other.

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Titration

A method of determining the concentration of an unknown acid or base by reacting it with a known solution of acid or base until neutralization occurs.

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Equivalence Point

The point in a titration where the acid and base have reacted in stoichiometric proportions, as defined by the balanced chemical equation.

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Titration Curve

A graph that plots the pH of the analyte solution against the volume of titrant added during a titration.

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Half-Equivalence Point

The point in a titration where the volume of titrant added is half the volume needed to reach the equivalence point.

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Standard Solution

A solution with a known, accurate concentration used in titrations, often prepared with a primary standard.

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Primary Standard

A pure substance, like potassium hydrogen phthalate (KHP), used to prepare solutions of accurately known concentrations.

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Volumetric Analysis

A quantitative analytical technique that measures the volume of a solution with a known concentration to determine the concentration of an unknown solution.

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Neutralization Reaction

A chemical reaction where an acid and a base react to form a salt and water.

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Study Notes

Chemical Equilibrium Systems

  • A system is any part of the universe being studied, such as an ocean or a test tube.
  • An open system interacts with its surroundings, allowing both energy and matter to move in and out.
  • A closed system only exchanges energy with its surroundings, not matter. Equilibrium in a closed system occurs when the rates of forward and reverse reactions are equal.

Chemical Equilibrium

  • Reactions can occur in both forward and reverse directions.
  • A system is at equilibrium when the forward and reverse reactions continue, but there are no further changes in concentration.
  • Physical changes are usually reversible, for example, the changes of state of water (ice, liquid, gas).
  • Many chemical reactions are also reversible in a closed system.

Reversible Reactions

  • A reversible reaction is one where the products can react to reform the reactants.
  • Forward and reverse reactions can happen simultaneously.
  • These reactions are shown using energy profile diagrams.
  • The rates of the forward and reverse reactions equal at equilibrium.
  • The reaction is in chemical equilibrium when the rates of the forward and reverse reactions are equal and the concentrations of the reactants and products remain unchanged.

Extent of Reaction

  • Different reactions proceed to different extents, meaning the ratio of reactants to products is different for each reaction at equilibrium.
  • The extent of a reaction describes how far the reaction goes in the forward direction when equilibrium is reached and how much product is formed.

Le Chatelier's Principle

  • If a stress is applied to a system in equilibrium, the system will shift to relieve the stress.
  • Items considered as stress are:
    • Concentration
    • Temperature
    • Pressure

Effect of Temperature on Equilibrium Constant

  • The value of $K_{eq}$ depends only on the temperature.
  • For exothermic reactions, increasing the temperature shifts the equilibrium position to the left, causing $K_{eq}$ to decrease.
  • For endothermic reactions, increasing the temperature shifts the equilibrium position to the right, causing $K_{eq}$ to increase.

Equilibrium Constants

  • Chemists use numerical values to describe equilibrium positions.
  • The equilibrium constant, $K_{eq}$, relates the concentrations of reactants and products at equilibrium.
  • $K_c$ refers to concentration, and $K_p$ refers to pressures.

Acid-Base Chemistry

  • Acids turn litmus red, are corrosive, and taste sour.
  • Bases turn litmus blue, are caustic, and feel slippery.
  • The Brønsted–Lowry model describes acid-base reactions as proton transfer.
  • Strong acids and bases completely dissociate in water.
  • Weak acids and bases partially dissociate.

Acid Dissociation Constant

  • The acid dissociation constant ($K_a$) is the ratio of the concentration of the dissociated form of an acid to the concentration of the undissociated form.

Base Dissociation Constant

  • The base dissociation constant ($K_b$) is the ratio of the concentration of the conjugate acid of a base and the hydroxide ion to the base concentration.

Calculating Dissociation Constants

  • Initial molar concentration of the acid.
  • Concentration of H+ (or pH) of the system at equilibrium.

Titration Curves

  • A graph of pH against the volume of reactant added.

  • The equivalence point in a titration is when the reactants have reacted in the molar ratio.

  • The endpoint is when the indicator changes color.

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Chemistry Unit 3 Notes PDF

Description

Test your knowledge on essential concepts in acid-base chemistry, including pH, electrolytes, and buffer solutions. This quiz covers key definitions and relationships, such as the self-ionization of water and the properties of amphoteric substances.

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