Analytical Chemistry Lecture 2: Volumetric Analysis
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Questions and Answers

What is the mole fraction of methyl alcohol in a 5.2 molal aqueous solution of CH3OH?

  • 0.086 (correct)
  • 1.100
  • 0.050
  • 0.190

    • What is the normality of a 2 M H2SO4 solution?

  • 1
  • 4
  • 2 (correct)
  • 6

    • Which of the following acids is a weak acid?

  • HF (correct)
  • HClO3
  • H2SO4
  • HCl

    • What is the mole fraction of C2H5OH in a solution that contains 46 grams of ethanol and 64 grams of methanol?

    <p>0.42</p> Signup and view all the answers

    What is the concentration of a solution prepared by dissolving 5g of NaCl in 500 ml of distilled water in ppm?

    <p>1000 ppm</p> Signup and view all the answers

    What is a Lewis base?

    <p>A chemical compound that has the tendency to donate an electron pair</p> Signup and view all the answers

    What is the definition of an acid according to the Arrhenius theory?

    <p>A substance that increases the concentration of the hydronium ion when dissolved in water</p> Signup and view all the answers

    What happens to the equilibrium when HB > HS+ in the leveling effect?

    <p>The equilibrium lies to the right</p> Signup and view all the answers

    What is the limitation of the Arrhenius theory?

    <p>It does not account for the existence of hydronium ions and hydroxide ions in solution</p> Signup and view all the answers

    What is the effect of a less basic solvent on the dissociation of acids?

    <p>Acids are not leveled and HClO4 is stronger than the other</p> Signup and view all the answers

    What is the definition of a Brønsted-Lowry acid?

    <p>A substance that donates a proton</p> Signup and view all the answers

    What is the conjugate base of an acid?

    <p>Everything that remains of the acid molecule after a proton is lost</p> Signup and view all the answers

    What is a characteristic of a strong acid?

    <p>It dissociates completely in water to produce H+(aq)</p> Signup and view all the answers

    What is the advantage of the Brønsted-Lowry theory over the Arrhenius theory?

    <p>It can explain the behavior of a wider range of substances</p> Signup and view all the answers

    What is the definition of a Lewis acid?

    <p>A substance that has a tendency to accept an electron pair</p> Signup and view all the answers

    What is the characteristic of a weak acid in an equilibrium reaction?

    <p>The equilibrium lies far to the left</p> Signup and view all the answers

    What is the correct formula for calculating the pH of a strong acid solution?

    <p>pH = -log [H+]</p> Signup and view all the answers

    What is the correct formula for calculating the concentration of OH- in a solution?

    <p>[OH-] = Kw/[H+]</p> Signup and view all the answers

    What is the result of the equation pH + pOH = pKw?

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

    What is the characteristic of the conjugate base of a weak acid?

    <p>It is a relatively strong conjugate base</p> Signup and view all the answers

    Study Notes

    Volumetric Analysis

    • Volumetric analysis is a type of quantitative analysis that involves the measurement of the volume of a solution required to react with a known volume of another solution.

    Weak Acids

    • A weak acid is an acid that does not dissociate completely in water, but instead reaches an equilibrium.
    • Examples of weak acids include phosphoric acid (H3PO4), acetic acid (CH3COOH), and benzoic acid (C6H5COOH).
    • A weak acid has a strong conjugate base.

    Strong Acids

    • A strong acid is an acid that dissociates completely in water to produce H+ (aq).
    • Examples of strong acids include hydrochloric acid (HCl), sulfuric acid (H2SO4), and perchloric acid (HClO4).
    • The equilibrium of a strong acid lies far to the right, meaning that almost all the original acid is dissociated.

    Acid Strength

    • Acid strength is defined by the equilibrium position of its dissociation reaction.
    • A strong acid is one for which the equilibrium lies far to the right, meaning that almost all the original acid is dissociated.
    • A weak acid is one for which the equilibrium lies far to the left, meaning that only a small amount of the acid is dissociated.

    Arrhenius Theory of Acids and Bases

    • Arrhenius theory states that an acid is a substance that increases the concentration of H+ ions in solution, while a base is a substance that increases the concentration of OH- ions in solution.
    • The theory is limited in that it only applies to substances that dissolve in water and does not account for the acidic or basic properties of substances in non-aqueous solutions.

    Brønsted-Lowry Theory of Acids and Bases

    • Brønsted-Lowry theory states that an acid is a substance that donates a proton (H+), while a base is a substance that accepts a proton.
    • The theory is more comprehensive than Arrhenius theory and can be applied to substances in both aqueous and non-aqueous solutions.

    Lewis Theory of Acids and Bases

    • Lewis theory states that an acid is a substance that accepts an electron pair, while a base is a substance that donates an electron pair.
    • The theory is more comprehensive than Arrhenius and Brønsted-Lowry theories and can be applied to substances in both aqueous and non-aqueous solutions.

    The Leveling Effect

    • The leveling effect refers to the phenomenon where the strength of an acid is governed by the solvent in which it is dissolved.
    • In a solvent with a high dielectric constant, such as water, acids are leveled to a common strength.

    Calculation of pH

    • pH is calculated as -log[H3O+] or -log[H+].
    • The concentration of H+ ions can be calculated using the dissociation constant (Ka) and the initial concentration of the acid.

    Problems

    • Calculate the mole fraction of C2H5OH in a solution containing 46g of ethanol and 64g of methanol.
    • Calculate the molality of a 5.2 molal aqueous solution of methyl alcohol.
    • Calculate the concentration of a solution prepared by dissolving 5g of AgNO3 in 100ml of water.
    • Calculate the percentage by weight of a solution prepared by dissolving 200g of Na2SO4 in 500ml of water.
    • Calculate the molarity of a solution prepared by dissolving 4g of NaOH in 500ml of water.

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    Description

    This quiz covers volumetric analysis in analytical chemistry, including weak acids and calculating mole fractions in solutions.

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