Acid-Base Titrations and Curves
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Questions and Answers

What is a characteristic of a titration involving a strong acid and a strong base?

  • The pH change occurs gradually throughout the titration.
  • The volume of titrant required is significantly larger than that of the analyte.
  • The endpoint is typically marked by a steep rise in pH. (correct)
  • The color change happens before the endpoint is reached.

    • Which of the following statements about color indicators in acid-base titrations is false?

  • A good indicator should provide a clear visual cue when the pH changes.
  • The choice of indicator is not critical if the titration is between a weak acid and a strong base. (correct)
  • Indicators can show a distinct color change at the endpoint.
  • Strongly colored acids will affect the titration's endpoint.

    • Which of the following substances would likely not be appropriate for use as an acid in a typical titration with NaOH?

  • NaCl (correct)
  • CH3COOH
  • HCl
  • H2SO4

    • In the titration of 100 mL of 0.1 M NaOH with 0.1 M HCl, what is the expected resultant solution at the equivalence point?

    <p>A neutral solution with pH 7.</p> Signup and view all the answers

    What role do organic weak acids or bases play in titrations compared to strong acids and bases?

    <p>They can act as effective indicators when strongly colored.</p> Signup and view all the answers

    What is the effect of combining 100 mL of 0.1 M HCl with an equal volume of 0.1 M NaOH during a titration?

    <p>The resulting solution will be neutral.</p> Signup and view all the answers

    Which of the following species is the main contributor to the pH at the equivalence point of the titration of HCl with NaOH?

    <p>H2O</p> Signup and view all the answers

    During the titration of HCl with NaOH, which reaction occurs when the strong acid neutralizes the strong base?

    <p>HCl + NaOH → NaCl + H2O</p> Signup and view all the answers

    How would the titration curve for 0.1 M HCl versus 0.1 M NaOH change if 0.1 M nitric acid was used instead of hydrochloric acid?

    <p>The curve would remain unchanged.</p> Signup and view all the answers

    What will the pH of the solution be just before reaching the equivalence point during the titration of HCl with NaOH?

    <p>Below 7</p> Signup and view all the answers

    What is the pH of the solution after 10.0 mL of NaOH is added to the titration of 0.1M HOAc?

    <p>4.1556</p> Signup and view all the answers

    At the midpoint of the titration of HOAc with NaOH, what relationship holds true?

    <p>pH = pKa</p> Signup and view all the answers

    What is the concentration of OAc- at the equivalence point in the titration of 50.0 mL 0.1M HOAc with 0.1M NaOH?

    <p>0.05 M</p> Signup and view all the answers

    What is the primary factor determining the pH after the equivalence point in this titration?

    <p>Excess NaOH concentration</p> Signup and view all the answers

    During the buffer region of the titration, how is the concentration of HOAc calculated?

    <p>Ca = (CHAVa - CbVb)/(Va + Vb)</p> Signup and view all the answers

    What is the value of [H3O+] when 25.0 mL of NaOH is added during the titration?

    <p>1.75 x 10-5 M</p> Signup and view all the answers

    What determines the color of a solution containing an acid-base indicator?

    <p>The concentration of HIn relative to In-</p> Signup and view all the answers

    At which condition will you observe Color A in the indicator system?

    <p>When [HIn]/[In-] is greater than 10:1</p> Signup and view all the answers

    What is the significance of the pKa in relation to the indicator color change?

    <p>It defines the pH range for color change of the indicator</p> Signup and view all the answers

    What relationship does the equation [H3O+] = Ka x [HIn]/[In-] express?

    <p>The dependence of hydronium ion concentration on indicator concentrations</p> Signup and view all the answers

    In the context of acid-base titrations using indicators, what pH corresponds to Color B?

    <p>pH = pKa + 1</p> Signup and view all the answers

    If the ratio of [HIn]/[In-] is below 10:1, what is the likely observed color?

    <p>Color B</p> Signup and view all the answers

    What is the pH transition range for an acid-base indicator based on its pKa?

    <p>pH = pKa ± 1</p> Signup and view all the answers

    Study Notes

    Acid-Base Titrations

    • Titration is a technique used to determine the concentration of an unknown solution (analyte) by reacting it with a solution of known concentration (titrant).
    • Neutralization reactions are common in acid-base titrations.
    • Acidimetry involves the quantitative determination of basic drugs.
    • Alkalimetry involves the quantitative determination of acidic drugs.
    • Strong acids and bases completely dissociate in water.
    • The stoichiometric ratio of the acid-base reaction needs to be known.
      • Example: HCl + NaOH → HOH + Na⁺ + Cl⁻, the stoichiometric ratio is 1:1.
    • Equilibrium needs to be considered, like Kw = [H₃O⁺][OH⁻] = 10⁻¹⁴

    Titration Curves for Strong Acids and Bases

    • The pH before titration begins can be calculated using the given concentration of the analyte.
    • pH calculation before equivalence point can be calculated by knowing the concentrations of the acid and base, along with the volumes of those substances. 
      • Example: [H₃O⁺] = ((Cacid Vacid - Cbase Vbase)/(Vacid + Vbase) * consider acid volume in litres, and the base volume in litres, and their respective concentrations in Moles/Litres
    • pH at equivalence point is determined by the autodissociation of water.
      • Example: Kw = [H3O⁺] [OH⁻) = 10⁻¹⁴ which leads to pH = 7.0000 (4s.f.)

    Titration Curves for Weak Acids and Bases

    • Differences in titration curves of weak acid/base solution vs strong acid/base solution:
      • The end point break in the weak acid/base titration curves are smaller than that of strong acid/base titration curves.
      • The selection of indicator is critical in weak acid/base titration than strong acid/base titration
    • The midpoint on the titration curve of a weak acid/base occurs at pH = pKa.
    • The equivalence point pH changes depending on if the substance being titrated is an acid or base
      • If a weak acid is titrated, a buffer region exists before the equivalence point. If a weak base is titrated, a buffer region will also exist before the equivalence point.

    Polyfunctional Acids/Bases

    • Polyfunctional acids have multiple ionizable protons (e.g., H₃PO₄).
    • Polyfunctional bases have multiple ionizable hydroxide ions (e.g., ethylenediamine).
    • Separate equivalence points are observed in the titration curves if the ratios of successive dissociation constants are greater than approximately 10⁴ .
    • Equivalence points can be observed in the titration curves for dissociation steps where Kₐ is greater than approximately 10⁻⁸.

    Acid-Base Color Indicators

    • Indicators are organic weak acids or bases that change colour over a specific pH range.
    • The indicator's colour change from acid form to conjugate base form is distinct.
    • The indicator's ratio of concentrations of the acid form to conjugate base form (HIn/In⁻) determines the solution's colour.
    • pH = pKa ± 1, the indicator changes colour between pH = pKa - 1 and pKa + 1.

    Amino Acids

    • Amino acids are polyprotic, containing both a carboxyl group and an amino group.
    • The isoelectric point (pI) is the pH at which an amino acid or the ion of an amino acid has zero net charge.
    • Titration of amino acids reveals multiple equivalence points due to their multiple ionizable protons.

    Direct Titration Methods

    • Direct titration methods are used for analyzing substances using standard solutions.

    Indirect Titration Methods

    • Indirect titration methods, also known as residual or back titrations, determine the concentration of substances by reacting with a known excess of a standard solution, then titrating the remaining unreacted excess.

    Additional Notes

    • There are different types of titrations (e.g., strong acid/strong base, weak acid/strong base, strong base/weak acid, weak base/strong acid etc.). Different titrations give different titration curves. There can be graphs, tables, equations etc. that go along with specific titrations.
    • Titration curves can be used to determine equivalence points, select indicators, determine pH at equivalence points etc.

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    Acid-Base Titrations Chapter 8 PDF

    Description

    Explore the concepts of acid-base titrations and the calculation of pH in various scenarios. This quiz covers neutralization reactions, stoichiometric ratios, and titration curves for strong acids and bases. Test your understanding of these essential chemistry principles.

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