Questions and Answers
What does a pH less than 7 indicate?
What is the pH of 0.01M HCl?
2
What is the pKa value of the weak acid acetic acid (HC2H3O2)?
4.76
What is the pH of 0.01M H2SO4?
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What is the relationship between pKa and Ka?
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What is the pH of 10M CsOH?
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Kw is the equilibrium constant for __________ dissociating in water.
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HCl is a weak acid.
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What happens to the pH of pure water at 37 degrees Celsius?
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What is the Kb expression for a weak base?
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What occurs to the relationship between Kb and pKb for weak bases?
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Study Notes
pH Basics
- pH scale: <7 indicates acidity and >7 indicates alkalinity.
- Strong acids fully dissociate, while weak acids do not.
Strong Acids
- HCl (0.01M): Fully dissociates into H+ and Cl-.
- [H+] = 0.01M results in pH 2.
- Acetic acid (HC2H3O2): Weak acid (Ka not provided); will have a pH < 2 if 0.1M.
- H2SO4 (0.01M): Diprotic acid; first H fully dissociates, resulting in pH ~2.
- Second proton in H2SO4 is weakly acidic and contributes minimally to [H+].
Strong Bases
- NaOH (0.01M): Fully dissociates, yielding [OH-] = 0.01M.
- pOH 2 results in pH 12.
- Ba(OH)2 (0.01M): Gives [OH-] = 0.02M leading to pH 12.3.
- CsOH (10M): Results in very high [OH-] of 10M, pH 15.
Weak Acids and Ka
- Acetic acid (0.1M HC2H3O2): Ka = 1.75 x 10^-5.
- Ka expression: Ka = [H+][A-]/[HA].
- Simplifying: at equilibrium, [H+] = √(Ka × HA).
- Calculation shows [H+] ~ 1.3 x 10^-3, resulting in pH ~2.9.
Weak Bases and Kb
- Kb indicates the strength of weak bases, defined by the equilibrium: A- + H2O ⇌ OH- + HA.
- Kb expression: Kb = [OH-][HA]/[A-].
- Determining [OH-]: [OH-] = √(Kb × [A-]).
Water Equilibrium Constant (Kw)
- Kw = [H+][OH-] = 1.0 x 10^-14 at 25°C.
- Change in temperature affects Kw.
- Relationship: Ka × Kb = Kw; pKa + pKb = 14.
- Stronger acids have higher Ka and correspondingly lower Kb for conjugate bases.
Temperature Effects on pH
- In pure water, [H+] = [OH-], leading to pH 7.
- Acidic solutions: [H+] > [OH-].
- Basic solutions: [OH-] > [H+].
- Neutral pH shifts with temperature changes; at 37°C, pH 7 is considered basic if Kw increases.
Acid and Base Strength
- Stronger acids have larger Ka, resulting in smaller pKa values.
- Stronger bases have larger Kb, resulting in smaller pKb values.
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Description
Explore the fundamental concepts of pH levels in strong and weak acids through interactive flashcards. This quiz covers the definitions and calculations necessary to understand how the pH of various acids is determined and the implications for acidity and basicity.
