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Questions and Answers
According to the Brønsted-Lowry definition, what is the primary characteristic of a base?
According to the Brønsted-Lowry definition, what is the primary characteristic of a base?
- It donates protons.
- It produces hydronium ions in water.
- It accepts protons. (correct)
- It donates hydroxide ions in solution.
Which statement best describes the dissociation of a strong acid in an aqueous solution?
Which statement best describes the dissociation of a strong acid in an aqueous solution?
- It partially dissociates, reaching equilibrium with its conjugate base.
- It dissociates completely, producing a high concentration of hydronium ions. (correct)
- It forms a buffer solution, resisting pH changes.
- It does not dissociate and remains as undissociated molecules.
How does the value of Ka relate to the strength of an acid?
How does the value of Ka relate to the strength of an acid?
- The Ka is only relevant for bases.
- The higher the Ka the stronger the acid. (correct)
- The lower the Ka the stronger the acid.
- The Ka value is not related to the strength of an acid.
What is the significance of the equivalence point in an acid-base titration?
What is the significance of the equivalence point in an acid-base titration?
A solution is found to have a pKa of 4.75. What is this an indicator of?
A solution is found to have a pKa of 4.75. What is this an indicator of?
Which statement accurately describes the relationship between $K_a$ and $K_b$ for a conjugate acid-base pair?
Which statement accurately describes the relationship between $K_a$ and $K_b$ for a conjugate acid-base pair?
What is the primary function of a buffer solution?
What is the primary function of a buffer solution?
The hydroxide concentration in solution from a group 2 metal hydroxide will be, compared to the initial concentration of the base:
The hydroxide concentration in solution from a group 2 metal hydroxide will be, compared to the initial concentration of the base:
What factor is NOT considered to influence the strength of an acid or a base?
What factor is NOT considered to influence the strength of an acid or a base?
In the Henderson-Hasselbalch equation, when the pKa is equal to the pH, what can be said about the concentrations of the acid and conjugate base?
In the Henderson-Hasselbalch equation, when the pKa is equal to the pH, what can be said about the concentrations of the acid and conjugate base?
Which condition describes when a buffer is most effective?
Which condition describes when a buffer is most effective?
What happens when a conjugate base of a weak acid is added to a solution?
What happens when a conjugate base of a weak acid is added to a solution?
How is buffer capacity affected?
How is buffer capacity affected?
Which of the following best describes an acid-base titration?
Which of the following best describes an acid-base titration?
What indicates the equivalence point in a titration?
What indicates the equivalence point in a titration?
What is the consequence of a weak acid having a high pKa value?
What is the consequence of a weak acid having a high pKa value?
What determines the pH at the equivalence point of a titration involving a weak acid and a strong base?
What determines the pH at the equivalence point of a titration involving a weak acid and a strong base?
Which factor does NOT affect the stability of a conjugate base?
Which factor does NOT affect the stability of a conjugate base?
When both an acid and a base are in a solution, which will determine the pH primarily?
When both an acid and a base are in a solution, which will determine the pH primarily?
What condition indicates the point at which the concentrations of the acid and its conjugate base are equal, according to the pH and pKa relationship?
What condition indicates the point at which the concentrations of the acid and its conjugate base are equal, according to the pH and pKa relationship?
Which statement accurately describes the buffer action when a strong acid is added to a buffer solution?
Which statement accurately describes the buffer action when a strong acid is added to a buffer solution?
Which of the following best describes the relationship between hydronium and hydroxide ion concentrations in pure water at 25°C?
Which of the following best describes the relationship between hydronium and hydroxide ion concentrations in pure water at 25°C?
A solution has a pH of 3. What is the best description of the solution?
A solution has a pH of 3. What is the best description of the solution?
If the temperature of water increases, what happens to the value of Kw?
If the temperature of water increases, what happens to the value of Kw?
Which of the following is not considered a strong acid?
Which of the following is not considered a strong acid?
What is the pH of a 0.01 M solution of HCl?
What is the pH of a 0.01 M solution of HCl?
A solution of $Ca(OH)_2$ has a concentration of 0.005M. What is the pOH of this solution?
A solution of $Ca(OH)_2$ has a concentration of 0.005M. What is the pOH of this solution?
Which of the following describes the relationship between a weak acid and its conjugate base?
Which of the following describes the relationship between a weak acid and its conjugate base?
Which scenario would result in a solution with a pH equal to 7?
Which scenario would result in a solution with a pH equal to 7?
A weak acid, HA, has a $K_a$ of $1.0 \times 10^{-5}$. If the initial concentration of HA is 0.10 M, what is the approximate concentration of $H_3O^+$ at equilibrium?
A weak acid, HA, has a $K_a$ of $1.0 \times 10^{-5}$. If the initial concentration of HA is 0.10 M, what is the approximate concentration of $H_3O^+$ at equilibrium?
Which of the following changes would result in a decrease in the pH of a solution?
Which of the following changes would result in a decrease in the pH of a solution?
A solution is prepared by mixing equal moles of a weak acid and its conjugate base. If the pKa of the weak acid is 4.5, what is the approximate pH of the solution?
A solution is prepared by mixing equal moles of a weak acid and its conjugate base. If the pKa of the weak acid is 4.5, what is the approximate pH of the solution?
A solution of ammonium chloride (NH4Cl) in water is:
A solution of ammonium chloride (NH4Cl) in water is:
If the percent ionization of a 0.20 M solution of a weak acid HA is 2%, what is the approximate value of $K_a$?
If the percent ionization of a 0.20 M solution of a weak acid HA is 2%, what is the approximate value of $K_a$?
Which statement is true regarding acid-base titrations that involve a weak acid and a strong base?
Which statement is true regarding acid-base titrations that involve a weak acid and a strong base?
A buffer solution has a pH of 5.0. If we add a small amount of a strong acid, which of the following is the primary change occurring in the buffer?
A buffer solution has a pH of 5.0. If we add a small amount of a strong acid, which of the following is the primary change occurring in the buffer?
For a given weak acid, which of these relationships is INCORRECT?
For a given weak acid, which of these relationships is INCORRECT?
Given two buffer solutions: Solution A is 0.2 M in both a weak acid and its conjugate base and Solution B is 0.4 M in both. Which solution has a greater buffer capacity?
Given two buffer solutions: Solution A is 0.2 M in both a weak acid and its conjugate base and Solution B is 0.4 M in both. Which solution has a greater buffer capacity?
A salt is formed in the following reaction: $HCl(aq) + NaOH(aq) \rightarrow NaCl(aq) + H_2O(l)$. How will the $NaCl$ salt affect the pH of water?
A salt is formed in the following reaction: $HCl(aq) + NaOH(aq) \rightarrow NaCl(aq) + H_2O(l)$. How will the $NaCl$ salt affect the pH of water?
Which of the following best describes why a weaker bond in an acid leads to a stronger acid?
Which of the following best describes why a weaker bond in an acid leads to a stronger acid?
What does the value of the ionization constant, $K_b$, indicate about the strength of a base?
What does the value of the ionization constant, $K_b$, indicate about the strength of a base?
For a weak acid with a pKa of 4.8, at what pH will the concentration of the acid form be approximately ten times greater than the concentration of the base form?
For a weak acid with a pKa of 4.8, at what pH will the concentration of the acid form be approximately ten times greater than the concentration of the base form?
A solution contains equal moles of a weak acid and its conjugate base. If a strong base is added, what will occur?
A solution contains equal moles of a weak acid and its conjugate base. If a strong base is added, what will occur?
Which of the following factors would cause a decrease in the pH of an aqueous solution of a weak acid?
Which of the following factors would cause a decrease in the pH of an aqueous solution of a weak acid?
Flashcards
Brønsted-Lowry definition
Brønsted-Lowry definition
Acids donate protons, while bases accept protons.
Arrhenius definition
Arrhenius definition
Acids produce hydrogen ions (H+) or hydronium ions (H3O+) in water, while bases produce hydroxide ions (OH-) in water.
Strong Acid
Strong Acid
Strong acids dissociate completely into ions in solution.
Weak Acid
Weak Acid
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Strong Base
Strong Base
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Weak Base
Weak Base
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Buffer Solution
Buffer Solution
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Acid-Base Titration
Acid-Base Titration
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What factors influence acid or base strength?
What factors influence acid or base strength?
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What is pKa?
What is pKa?
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How is pH related to pKa?
How is pH related to pKa?
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What is a buffer?
What is a buffer?
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What determines the pH of a buffer?
What determines the pH of a buffer?
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What is buffer capacity?
What is buffer capacity?
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What factors affect buffer capacity?
What factors affect buffer capacity?
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How do salts affect the pH of a solution?
How do salts affect the pH of a solution?
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How does adding a strong base or acid to a solution containing a weak acid/base change the pH?
How does adding a strong base or acid to a solution containing a weak acid/base change the pH?
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What is the equivalence point in an acid-base titration?
What is the equivalence point in an acid-base titration?
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What is the relationship between the pH at the halfway point and the pKa of the weak acid in a titration?
What is the relationship between the pH at the halfway point and the pKa of the weak acid in a titration?
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What determines the strength of an acid or base?
What determines the strength of an acid or base?
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What factors can influence the stability of a conjugate base?
What factors can influence the stability of a conjugate base?
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How do you predict the protonation state of an acid/base based on pH and pKa?
How do you predict the protonation state of an acid/base based on pH and pKa?
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How does the concentration of buffer components affect buffer capacity?
How does the concentration of buffer components affect buffer capacity?
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Buffer Capacity
Buffer Capacity
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pH
pH
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pOH
pOH
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Kw (Ion Product of Water)
Kw (Ion Product of Water)
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pKa
pKa
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Equivalence Point
Equivalence Point
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Water Autoionization
Water Autoionization
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Ka for Weak Acids
Ka for Weak Acids
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Kb for Weak Bases
Kb for Weak Bases
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ICE Table
ICE Table
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Percent Ionization
Percent Ionization
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Ions Affecting pH
Ions Affecting pH
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Predicting Salt Solution pH
Predicting Salt Solution pH
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Buffer pH
Buffer pH
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Henderson-Hasselbalch Equation
Henderson-Hasselbalch Equation
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Titration Curve
Titration Curve
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Acid-Base Strength
Acid-Base Strength
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Titration
Titration
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Equivalence Point pH
Equivalence Point pH
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Study Notes
Introduction to Acids and Bases
- Acids donate protons (H+) in chemical reactions; bases accept protons (H+).
- Brønsted-Lowry definition: Acids are proton donors, bases are proton acceptors.
- Arrhenius definition: Acids produce H+ (hydronium ions) in water, bases produce OH− (hydroxide ions) in water.
- Strong acids dissociate 100% in water; they have large Ka values (usually not mentioned).
- Weak acids dissociate less than 100% in water; they have smaller Ka values.
- Concentrations of H3O+ and OH− are often reported as pH and pOH, respectively.
- pH is the negative log of the H3O+ concentration.
- pOH is the negative log of the OH− concentration.
- Hydronium ion (H3O+) is preferred, but hydrogen ion (H+) is acceptable on the AP Chemistry Exam.
Water Autoionization and Kw
- Water ionizes naturally, producing equimolar amounts of H3O+ and OH−, with an equilibrium constant Kw.
- Kw = [H3O+][OH−] = 1.0 × 10−14 at 25°C.
- Pure water at 25°C is neutral, with pH = 7 and pOH = 7.
- pH of water can differ from 7 at temperatures other than 25°C due to temperature dependence of Kw.
- Kw increases with increasing temperature, indicating water autoionization is endothermic.
pH and pOH of Strong Acids and Bases
- Strong acids completely dissociate, producing H3O+ ions with the same concentration as the initial acid concentration.
- Six strong acids: HCl, HBr, HI, HNO3, HClO4, and H2SO4.
- Strong bases, hydroxides of Group 1 and 2 elements, completely dissociate, producing OH− ions.
- OH− concentration is equal to the initial base concentration, doubling for alkaline earth metals (Group 2).
- Calculating pH of a strong acid: Find molarity of strong acid, which equals molarity of H3O+; calculate pH using pH = -log[H3O+].
- Calculating pH of a strong base: Find molarity of strong base, doubling for alkaline earth hydroxides; calculate pOH using pOH = -log[OH−]; calculate pH using pH + pOH = 14.
Weak Acid and Base Equilibria
- Weak acids partially dissociate, establishing equilibrium between the acid and its conjugate base.
- Weak acids have Ka values found in tables/online.
- Ka expression: Ka = [H3O+][A−]/[HA].
- Increasing acid strength corresponds to higher Ka and [H3O+], and lower pH.
- Weak bases partially dissociate, establishing equilibrium between the base and its conjugate acid.
- Weak bases have Kb values found in tables/online.
- Kb expression: Kb = [BH+][OH−]/[B].
- Increasing base strength corresponds to higher Kb and [OH−], and higher pH.
- Ka × Kb = Kw.
- Use ICE tables to solve for pH of weak acid/base solutions.
Percent Ionization
- Percent ionization = [amount ionized / initial amount] × 100, where the amount ionized is represented by the 'x' variable.
Acid-Base Properties of Salts
- Ions from weak acids/bases can affect solution pH without H+ or OH−.
- Ions act as conjugates of weak acids/bases.
- Examples: Phosphate is a conjugate of a weak acid, in equilibrium with its conjugate acid.
- Phosphate can remove protons from water, creating OH− and affecting pH.
Predicting pH of Salt Solutions
- Chart to predict acidity/basicity of salt solutions. Separate salt into cation and anion.
- Imagine cation with OH− and anion with H+.
- Strong species have no pH effect; weak species affect pH.
- Cation with weak base form makes solution acidic.
- Anion with weak acid form makes solution basic.
Calculating pH of Salt Solutions
- Identify ions with acidic/basic properties.
- Write equilibrium equation for relevant ion.
- Use Ka or Kb values to find equilibrium constant.
- Solve for H+ or OH− concentration.
- Calculate pH using relevant formula.
Acid-Base Reactions and Buffers
- Strong acid/strong base reactions are quantitative.
- pH of resulting solution determined by excess reactant.
- Weak acid with strong base: Strong base reacts with weak acid, producing conjugate base and water; if weak acid in excess, buffer forms (weak acid + conjugate base). Calculate buffer pH using Henderson-Hasselbalch. If strong base in excess, highly basic solution. Equimolar reactants result in a slightly basic solution.
- Similar for weak base with strong acid.
Buffer Diagrams
- Diagrams illustrate buffer reactions.
- Acid addition: Protons react with conjugate base, producing more weak acid.
- Base addition: Hydroxide ions react with weak acid, producing more conjugate base and water.
Buffer Calculations
- Henderson-Hasselbalch equation: pH = pKa + log([conjugate base]/[acid]).
- Ratio can be expressed in any units, as long as it represents relative concentrations.
Acid-Base Titrations
- Titration determines concentration of unknown solution (analyte) with known concentration solution (titrant).
- Titration curve plots pH vs. volume of titrant.
- Equivalence point: Moles of titrant = moles of analyte; often indicated by indicator color change.
- pH at equivalence point depends on acid/base strengths: strong acid/strong base (pH = 7), weak acid/strong base (pH > 7), weak base/strong acid (pH < 7).
- pH halfway to equivalence point equals pKa of weak acid/base.
Factors Influencing Acid Strength
- Bond strength and polarity determine acidity. Weaker bond, more polar bond = stronger acid.
- Electronegative elements stabilize conjugate base, increasing acid strength.
- Carboxylic acids are common weak acids. Strong bases (Group 1/2 hydroxides) have very weak conjugate acids.
pH and pKa
- Comparing solution pH to acid pKa predicts protonation state.
- pH < pKa: More acid form.
- pH > pKa: More conjugate base form.
- pH = pKa: Equal concentrations of acid and conjugate base forms.
Buffer Capacity
- Buffer capacity is solution resistance to pH change upon addition of acid/base.
- Determined by buffer component concentrations. Increased concentrations lead to higher buffer capacity. Buffers are most effective when the pKa of the weak acid is near the desired pH. More conjugate acid than base leads to greater capacity for added base; more conjugate base than acid leads to greater capacity for added acid.
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Description
Explore the fundamentals of acids and bases, including their definitions, behavior in solution, and pH levels. Understand the differences between strong and weak acids and bases, and how their dissociation affects their strength. This quiz covers critical concepts necessary for mastering acid-base chemistry.
