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Questions and Answers
Which statement correctly describes an Arrhenius acid?
Which statement correctly describes an Arrhenius acid?
What happens to the charge of a molecule when it acts as a Brønsted-Lowry base?
What happens to the charge of a molecule when it acts as a Brønsted-Lowry base?
What pH range indicates a basic solution?
What pH range indicates a basic solution?
Which of the following is classified as a strong acid?
Which of the following is classified as a strong acid?
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What is the conjugate acid of NH3?
What is the conjugate acid of NH3?
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Which of the following will turn red litmus paper blue?
Which of the following will turn red litmus paper blue?
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What is the relationship between pH and pOH at 25°C?
What is the relationship between pH and pOH at 25°C?
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Which of the following is a characteristic property of acids?
Which of the following is a characteristic property of acids?
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What does a high Ka value indicate about an acid?
What does a high Ka value indicate about an acid?
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How is the strength of a base indicated in terms of Kb?
How is the strength of a base indicated in terms of Kb?
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Which of the following is true regarding the behavior of strong acids in solution?
Which of the following is true regarding the behavior of strong acids in solution?
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What occurs to Kw as the temperature increases?
What occurs to Kw as the temperature increases?
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What is the role of water in acid-base chemistry?
What is the role of water in acid-base chemistry?
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How can you calculate pH from hydronium ion concentration?
How can you calculate pH from hydronium ion concentration?
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What distinguishes a Brønsted-Lowry acid from an Arrhenius acid?
What distinguishes a Brønsted-Lowry acid from an Arrhenius acid?
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What describes the difference between strong and weak bases?
What describes the difference between strong and weak bases?
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Which equation represents the relationship between pKa and pKb at 25°C?
Which equation represents the relationship between pKa and pKb at 25°C?
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What characterizes Lewis acids and bases?
What characterizes Lewis acids and bases?
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Study Notes
Identifying Acids and Bases
- Acids typically contain hydrogen at the beginning of their chemical formula.
- Bases usually contain a hydroxide ion (OH-).
- A hydrogen attached to a nonmetal is generally an acid, while a hydrogen attached to a metal is usually a base.
- Acids are usually positively charged, while bases are negatively charged.
Arrhenius Definition
- An Arrhenius acid releases H+ ions in solution.
- An Arrhenius base releases OH- ions in solution.
- H+ ions in water are bonded to water molecules and exist as hydronium ions (H3O+).
Brønsted-Lowry Definition
- A Brønsted-Lowry acid is a proton (H+) donor.
- A Brønsted-Lowry base is a proton acceptor.
- In a reaction between an acid and a base, the acid forms a conjugate base (by losing a proton), and the base forms a conjugate acid (by gaining a proton).
Writing Conjugate Acids and Bases
- To find the conjugate acid, add an H+ to the molecule and increase the charge by 1.
- To find the conjugate base, remove an H+ from the molecule and decrease the charge by 1.
pH Scale
- The pH scale ranges from 0 to 14, with the possibility of going beyond those limits.
- pH 7 is neutral.
- pH below 7 is acidic.
- pH above 7 is basic.
- pH = -log[H3O+].
- pOH = -log[OH-].
- pH + pOH = 14 at 25°C.
Strong Acids and Bases
- Strong acids ionize completely in solution, forming strong electrolytes.
- Strong bases are soluble ionic compounds that ionize completely in solution, forming strong electrolytes.
- Strong acids form strong electrolytes; weak acids form weak electrolytes.
- Strong bases form strong electrolytes; weak bases form weak electrolytes.
Common Strong Acids
- HCl
- HBr
- HI
- HNO3 (nitric acid)
- H2SO4 (sulfuric acid)
- HClO4 (perchloric acid)
Weak Acids
- HF
- NH4+ (ammonium ion)
- CH3COOH (acetic acid)
Strong Bases
- KOH (potassium hydroxide)
- NaOH (sodium hydroxide)
- Ba(OH)2 (barium hydroxide)
Weak Bases
- NH3 (ammonia)
- F- (fluoride)
- NO2- (nitrite)
- CH3COO- (acetate)
- CN- (cyanide)
- HSO3- (bisulfite)
Strong Bases Other than Hydroxides
- O2- (oxide)
- H- (hydride)
Properties of Acids and Bases
- Acids taste sour.
- Bases taste bitter.
- Acids turn blue litmus paper red.
- Bases turn red litmus paper blue.
- Acids react with active metals to produce hydrogen gas.
Acid Dissociation Constant (Ka)
- Ka = [H3O+][A-] / [HA] (where HA is the acid)
- A higher Ka value indicates a stronger acid.
- pKa = -log(Ka).
- Strong acids have large Ka values and small pKa values.
- Weak acids have small Ka values and large pKa values.
Base Dissociation Constant (Kb)
- Kb = [OH-][BH+]/[B] (where B is the base)
- pKb = -log(Kb)
Autoionization of Water
- Water can act as both an acid and a base.
- Kw = [H3O+][OH-] = 1 x 10^-14 at 25°C.
- As temperature increases, Kw increases.
Amphoteric Substances
- Amphoteric substances can act as both acids and bases.
- Water is an amphoteric substance.
- H2PO4- is also an amphoteric substance.
- The conjugate base of a weak acid is a weak base.
Reactions between Acids and Bases
- Strong acids ionize completely in solution, so their reactions are represented with single arrows.
- Weak acids ionize partially in solution, so their reactions are represented with double arrows indicating a reversible process.
- Strong bases ionize completely in solution, forming strong electrolytes.
- Weak bases ionize partially in solution, forming weak electrolytes.
Mechanisms of Acid-Base Reactions
- The mechanism of reactions between acids and bases involves the transfer of protons (H+) from the acid to the base.
- The lone pairs of electrons on the base can be used to attack the hydrogen atom of the acid, breaking the bond and forming a new bond with the base.
Summary of Definitions for Acids
- Arrhenius Acid: Releases H+ ions in solution.
- Brønsted-Lowry Acid: Proton donor.
- Lewis Acid: Electron pair acceptor.
Summary of Definitions for Bases
- Arrhenius Base: Releases OH- ions in solution.
- Brønsted-Lowry Base: Proton acceptor.
- Lewis Base: Electron pair donor.
pH and pOH
- At 25°C, the product of the concentrations of hydronium ions (H3O+) and hydroxide ions (OH-) is equal to 1 x 10^-14.
- This is represented by the equation: [H3O+] x [OH-] = Kw = 1 x 10^-14
- The pH and pOH of a solution at 25°C are related by the equation: pH + pOH = 14
- pH is the negative logarithm of the hydronium ion concentration: pH = -log[H3O+]
- pOH is the negative logarithm of the hydroxide ion concentration: pOH = -log[OH-]
Ka and Kb
- Ka (acid dissociation constant) measures the strength of an acid.
- Kb (base dissociation constant) measures the strength of a base.
- The product of Ka and Kb for a conjugate acid-base pair is equal to Kw: Ka x Kb = Kw
- pKa and pKb are related to Ka and Kb by the equations: pKa = -log(Ka) and pKb = -log(Kb).
- At 25°C, pKa + pKb = 14.
Acid-Base Definitions
- Arrhenius Acid: An acid releases H+ ions in solution.
- Arrhenius Base: A base releases OH- ions in solution.
- Brønsted-Lowry Acid: A proton (H+) donor.
- Brønsted-Lowry Base: A proton (H+) acceptor.
- Lewis Acid: An electron pair acceptor.
- Lewis Base: An electron pair donor.
Strong vs. Weak Acids and Bases
- Strong acids: Dissociate completely in solution, resulting in a high concentration of H+ ions and a low pH.
- Weak acids: Dissociate partially in solution, resulting in a lower concentration of H+ ions and a higher pH compared to strong acids with the same concentration.
- Strong bases: Dissociate completely in solution, resulting in a high concentration of OH- ions and a high pH.
- Weak bases: Dissociate partially in solution, resulting in a lower concentration of OH- ions and a lower pH compared to strong bases with the same concentration.
Relationship between Ka, pKa, Acid Strength
- A higher Ka value indicates a stronger acid.
- A lower pKa value indicates a stronger acid.
- The stronger the acid, the weaker its conjugate base.
Examples
- Hydrochloric acid (HCl) is a strong acid.
- Acetic acid (CH3COOH) is a weak acid.
- Sodium hydroxide (NaOH) is a strong base.
- Ammonia (NH3) is a weak base.
pH Scale
- The pH scale ranges from 0 to 14.
- pH less than 7 indicates an acidic solution.
- pH greater than 7 indicates a basic solution.
- pH of 7 indicates a neutral solution.
Metal Ions as Lewis Acids
- Metal cations with a high positive charge can act as Lewis acids, accepting electron pairs from water molecules.
- This can lead to the formation of H+ ions, making the solution acidic.
- For example, aluminum chloride (AlCl3) dissolved in water creates an acidic solution.
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Description
Test your understanding of acids and bases, their definitions, and their classifications. This quiz covers key concepts, including the Arrhenius and Brønsted-Lowry definitions, as well as how to write conjugate acids and bases. Perfect for chemistry students looking to refine their skills!
