Analytical Chemistry Lecture 2: Titrimetric Methods
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Questions and Answers

What is the concentration of HCl after adding 10.0 mL of NaOH?

  • 0.030 M
  • 0.100 M
  • 0.050 M (correct)
  • 0.150 M

    • What is the pH of the solution at the equivalence point?

  • 14.00
  • 7.00 (correct)
  • 1.00
  • 4.00

    • What is the moles relationship between HCl and NaOH at the equivalence point?

  • Moles HCl < Moles NaOH
  • Moles HCl > Moles NaOH
  • Moles HCl = 2 x Moles NaOH
  • Moles HCl = Moles NaOH (correct)

    • What is the final concentration of OH- after adding 30.0 mL of NaOH post-equivalence?

    <p>0.125 M (D)</p> Signup and view all the answers

    What pH corresponds to an initial concentration of 0.100 M in HCl?

    <p>1.00 (A)</p> Signup and view all the answers

    What is the pH level after the addition of 25mL NaOH to a strong acid?

    <p>7.00 (A)</p> Signup and view all the answers

    Which equation represents the pH before equivalence in a titration of a strong acid with a strong base?

    <p>-log(CaVa) - (CbVb) (D)</p> Signup and view all the answers

    What is the initial pH of a strong base titrated with a strong acid?

    <p>14 (B)</p> Signup and view all the answers

    What is a common limitation of precipitation titration?

    <p>Availability of suitable indicators (C)</p> Signup and view all the answers

    Which statement correctly describes the pH after adding 10.0mL of NaOH to a strong acid?

    <p>The pH increases to 1.6. (D)</p> Signup and view all the answers

    What type of titration involves the formation of an insoluble compound?

    <p>Precipitation titration (A)</p> Signup and view all the answers

    What is the pH after the addition of 25.10mL NaOH during the titration of a strong acid?

    <p>10.12 (D)</p> Signup and view all the answers

    What is the pH at equivalence for a titration of a strong acid with a strong base?

    <p>7.00 (D)</p> Signup and view all the answers

    What is the concentration of unreacted Cl– after adding 10.0 mL of Ag+?

    <p>2.50 x 10–2 M (D)</p> Signup and view all the answers

    At the equivalence point, what is the relationship between [Ag+] and [Cl–]?

    <p>[Ag+] = [Cl–] (D)</p> Signup and view all the answers

    What is the pCl at 35 mL of AgNO3 added?

    <p>7.82 (C)</p> Signup and view all the answers

    Which calculation is correct for determining the concentration of Ag+ after adding 35.0 mL of titrant?

    <p>1.18 x 10–2 M (A)</p> Signup and view all the answers

    What is the Ksp expression for AgCl?

    <p>[Ag+][Cl–] (C)</p> Signup and view all the answers

    What is the concentration of Cl– after determining the Ksp with [Ag+] at 1.18 x 10–2 M?

    <p>1.5 x 10–8 M (D)</p> Signup and view all the answers

    For which of the following applications is complexometric titration NOT important?

    <p>Color change reaction (C)</p> Signup and view all the answers

    What happens to the concentration of Ag+ after adding excess Ag+ beyond the equivalence point?

    <p>It increases. (B)</p> Signup and view all the answers

    What is the main characteristic of the Mohr method for end point detection?

    <p>Formation of a second color precipitate (C)</p> Signup and view all the answers

    In the Mohr method, what happens if excess CrO4-2 is used?

    <p>It leads to color change before the equivalent point (B)</p> Signup and view all the answers

    What is the stoichiometric relationship in the titration of Ag+ with Cl- in the provided example?

    <p>1 mole of Cl- reacts with 1 mole of Ag+ (B)</p> Signup and view all the answers

    What color change indicates the end point in the Volhard method?

    <p>From white to blood red (C)</p> Signup and view all the answers

    What is the pH range suitable for the Mohr method?

    <p>6 – 10 (A)</p> Signup and view all the answers

    What is the impact of using too little CrO4-2 in the Mohr method?

    <p>Excess Ag+ consumption leading to color appearance after equivalent point (B)</p> Signup and view all the answers

    What does the adsorption indicator method (Fajan’s method) rely on?

    <p>Adsorption of indicators on the precipitated surface (D)</p> Signup and view all the answers

    What is the equilibrium constant for the reaction between Ag+ and Cl- based on the provided Ksp?

    <p>$5.6 imes 10^9$ (A)</p> Signup and view all the answers

    What is the main purpose of a titration?

    <p>To determine the concentration of an analyte (D)</p> Signup and view all the answers

    What does the term 'equivalent point' refer to in titrimetric analysis?

    <p>The point where the amount of titrant added equals the analyte (C)</p> Signup and view all the answers

    Which of the following statements about titration errors is accurate?

    <p>Titration error is calculated using the formula $V_{equ} - V_{end point}$ (A)</p> Signup and view all the answers

    In which type of titration is a ligand-metal complex formed?

    <p>Complexometric titration (A)</p> Signup and view all the answers

    When is back-titration commonly used?

    <p>When the rate of the reaction is slow (D)</p> Signup and view all the answers

    What does an acid-base indicator typically indicate?

    <p>Observable physical changes related to pH (D)</p> Signup and view all the answers

    Which of the following statements about phenolphthalein is true?

    <p>It is suitable for strong acid and strong base titrations (D)</p> Signup and view all the answers

    Which type of standard solutions are known for their high purity?

    <p>Primary standard solutions (D)</p> Signup and view all the answers

    What is the value of [Cd2+] after calculation?

    <p>$1.64×10^{-10} M$ (C)</p> Signup and view all the answers

    Which equation is used to determine the potential at the equivalent point in a redox titration?

    <p>Nernst equation (A)</p> Signup and view all the answers

    At the equivalent point in the titration of Fe2+ with Ce4+, what is the formal potential calculated to be?

    <p>+1.23 V (A)</p> Signup and view all the answers

    What is the fraction of uncomplexed Cd2+ represented as?

    <p>$[Cd2+] / CCd$ (C)</p> Signup and view all the answers

    What is the calculated concentration of EDTA after titration?

    <p>$6.25×10^{-4} M$ (B)</p> Signup and view all the answers

    What occurs at the initial point of the titration curve before any Ce4+ is added?

    <p>E = +0.00 V (A)</p> Signup and view all the answers

    What is the stoichiometric relationship between Fe2+ and Ce4+ in the reaction?

    <p>Moles Fe2+ = moles Ce4+ (D)</p> Signup and view all the answers

    What happens to the potential E after the equivalent point in the titration?

    <p>E increases to +1.66 V (A)</p> Signup and view all the answers

    Flashcards

    Titration

    A method to determine the concentration of an analyte using a titrant of known concentration.

    Equivalent Point

    The point in a titration where the amount of titrant added equals the amount of analyte.

    End Point

    The point in a titration where a physical change (e.g., color change) indicates the equivalent point.

    Titration Error

    The difference between the equivalent point and the experimental end point.

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    Acid-Base Indicator

    A compound that changes color depending on pH.

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    Primary Standard Solution

    A solution with precisely known concentration, often used to prepare secondary solutions.

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    Back-titration

    A titration where an excess of standard solution is added, and a second titration is used to determine the remaining titrant.

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    Acid-Base Titration

    A titration based on the reaction between an acid and a base.

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    Moles calculation

    The relationship of moles for acid and base in a titration MaVa = MbVb

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    pH before equivalence point

    Determined by the excess acid concentration.

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    pH at equivalence point

    Determined by water dissociation.

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    pH after equivalence point

    Determined by excess base concentration.

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    Strong Acid/Strong Base Titration Initial pH

    Calculated using the concentration of the acid (or base) and the equation -log [Acid] (or 14 + log [Base]).

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    Strong Acid/Strong Base Titration Pre-equivalence pH

    Calculated by considering the remaining acid/base concentrations, adjusted for the titrant added, and using the equation provided in the content.

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    Strong Acid/Strong Base Titration Equivalence

    Point at which the moles of acid and base are equal; resulting in a pH of 7.00 (for strong acid/strong base titrations).

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    Strong Acid/Strong Base Titration Post-Equivalence pH

    Calculated using the excess titrant concentration and the equation provided in the content.

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    Weak Acid/Weak Base Titration Initial pH

    Calculated by using the pKa/pKb , initial concentration of the weak acid/base, and the appropriate logarithm formula from the text.

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    Weak Acid/Base Pre-equivalence pH

    The pH changes before equal moles are reached. Calculated using the logarithm and the appropriate formula specified in the text.

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    Precipitation Titration

    A type of titration involving the formation of an insoluble precipitate by reaction between analyte and titrant.

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    Argentometric Titration

    A specific type of precipitation titration utilizing silver nitrate (AgNO3) to determine halide concentrations.

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    Mohr Method

    A titration method where the endpoint is indicated by the formation of a colored precipitate.

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    Volhard Method

    An indirect titration method where excess silver ions are back titrated with thiocyanate to form a colored complex.

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    Fajan's Method

    A direct titration method where an adsorption indicator changes color when adsorbed on the precipitate.

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    What's a titration curve?

    A graph that shows the change in analyte concentration as a function of titrant volume. It helps visualize the transition from pre-equivalence point to post-equivalence point.

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    Pre-equivalence Point

    The point in a titration where the analyte is in excess, before the equivalence point.

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    Post-equivalence Point

    The point in a titration where the titrant is in excess, after the equivalence point.

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    What is pCl?

    pCl is the negative logarithm of the chloride ion concentration ([Cl-]) in a solution. It's a measure of the chloride ion activity, similar to pH for hydrogen ions.

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    Excess Cl-

    The amount of chloride ions that haven't reacted with the silver ions during a titration before the equivalence point.

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    How is [Ag+] calculated?

    The silver ion concentration ([Ag+]) is calculated using the solubility product constant (Ksp) of silver chloride (AgCl) and the known chloride ion concentration ([Cl-]).

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    Excess Ag+

    The amount of silver ions that haven't reacted with chloride ions during a titration after the equivalence point.

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    Complexometric Titration

    A type of titration where the reaction between the analyte and titrant involves the formation of a complex, a compound with a metal ion and a ligand.

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    Fraction of Uncomplexed Cd2+

    The portion of Cd2+ ions that are not bound to ligands in solution, represented by αCd2+.

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    pCd

    The negative logarithm of the concentration of uncomplexed Cd2+ ions in solution.

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    Redox Titration

    A type of titration where the reaction involves the transfer of electrons between the analyte and titrant.

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    Nernst Equation

    An equation used to calculate the potential of an electrochemical cell under non-standard conditions.

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    Formal Potential

    The standard potential of a half-reaction under specific conditions, such as a certain ionic strength.

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    Equivalence Point Potential

    The potential of the cell when stoichiometrically equivalent amounts of analyte and titrant have reacted.

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    Before Equivalence Point Potential

    The potential of the cell before the equivalence point is reached.

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    After Equivalence Point Potential

    The potential of the cell after the equivalence point is reached.

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    Study Notes

    Analytical Chemistry - Lecture 2: Titrimetric Methods of Analysis

    • Titration is a technique used to determine the concentration of an analyte using a known concentration of titrant.
    • The titrant is added to the analyte until the reaction is complete.
    • This is indicated by a color change (end point) or nearly equivalent point.
    • The equivalent point is when the amount of titrant added is stoichiometrically equivalent to the amount of analyte.
    • The difference between the equivalent point and the end point is called the titration error.

    End Points

    • End point: A physical change associated with the condition of chemical equivalence.
    • Common end points include changes in color due to reagents or indicators and changes in the potential of an electrode.
    • Titration error is the difference between the equivalent point and the end point.

    Back-Titration

    • Back-titration is a technique used when the reaction rate between the analyte and reagent is slow or when the standard solution lacks stability.
    • An excess of standard solution is added to the analyte.
    • The excess reagent is then titrated with a second standard solution.

    Classification of Titrimetric Methods

    • Titrimetric methods are categorized into four groups: acid-base, complexometric, redox, and precipitation titrations.

    Standard Solutions

    • Standard solutions are prepared from compounds of high purity.
    • Standard solutions are classified into primary and secondary standard solutions.

    Acid-Base Indicators

    • Indicators are compounds added to the analyte solution to indicate the end point or near equivalent point. Acid-base indicators are weak organic acids or bases that change color over different pH ranges.
    • Examples include thymol blue, methyl yellow, methyl orange, bromocresol green, methyl red, bromocresol purple, bromothymol blue, phenol red, cresol purple, phenolphthalein, thymolphthalein, and alizarin yellow GG. Each indicator has a specific pH range over which it changes color.

    Types of Acid-Base Indicators

    • Phthalein Indicators: Typically colourless in acidic solutions and show a colour change in basic solutions (e.g., phenolphthalein). They are suitable for titrations involving weak acids and strong bases.

    • Sulfonphthalein Indicators: These indicators exhibit two distinct color changes in different pH ranges within acidic, neutral, and moderately basic solutions. An example is Neutral Red.

    • Azo Indicators: Indicators like methyl orange and methyl red primarily change colour on the acid side of the pH scale. Suitable for weak base and strong acid titrations.

    • Universal Indicator: A mixture of indicators that shows different colors over a wide pH range (1-14). Color change aids in determining the pH value.

    Acid-Base Titration

    • Acid-base titrations are based on neutralization reactions like NaOH + HCl → NaCl + H₂O, where the reaction takes place in a 1:1 stoichiometric ratio.
    • Concentration determination is calculated using M₁V₁ = M₂V₂.

    Titration Curve

    • A plot of pH (or instrument reading) vs volume of titrant added. Two types of curves are sigmoidal and linear segment curves.

    Strong Acid vs. Strong Base Titration

    • Initial pH: Determined by the initial analyte concentration.
    • Pre-equivalence point: pH calculated by the amount of excess acid.
    • Equivalence point: pH = 7 (neutral)
    • Post-equivalence point: pH determined by excess base.

    Precipitation Titration

    • Precipitation titrations involve a precipitation reaction where an insoluble compound is formed from the analyte and titrant. Applications in this method are limited due to the lack of suitable indicators, slow reaction rates in dilute solutions, and limited indicator availability. The most vital precipitation reaction involves AgNO₃, which is known as argentometric titration. This technique determines the concentration of halides.

    End Point Detection Methods

    • Mohr method: A direct method using chromate as an indicator. Chloride is determined in the presence of chromate. The reaction of Ag⁺ with chromate yields a visible coloured precipitate. Conditions include controlled pH levels and limited excess of indicator chromate.

    • Volhard method: An indirect method involving back-titration. excess AgNO3 is titrated with SCN using a ferric alum indicator.

    • Fajans method: A direct method based on indicator adsorption. The indicator adsorbs on the precipitate surface, causing a color change.

    Complexometric Titration

    • Complexation reaction between titrant and analyte.
    • Important in applications like black-and-white photography.
    • Detection of colored complex using spectrophotometric methods.
    • Some soluble complex used in gravimetric and precipitation analysis. Using EDTA as a complexing agent is common.

    EDTA (Ethylene diamine tetraacetic acid)

    • An amino carboxylic acid with six binding sites (four carboxylate and two amino groups).
    • Acts as a hexadentate ligand. Forms strong complexes with metal ions except for alkali metals. Widely used to extract, dissolve, and/or bind metal ions to prevent interference, to extract metals between solvents, or form complexes for spectrophotometric analysis.

    Redox Titration

    • Redox reactions occur due to electron transfer. Potential is determined using the Nernst equation ( E = E° - (RT/nF) ln( [oxidized]/[reduced])).
    • EAox/Ared is the standard state potential for the half-reaction. At the equivalent point, potential calculation is simplified using the Nernst equation for the titrants half-reaction.

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    Analytical Chemistry Lecture 2: Titrimetric Methods PDF

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    Explore the fundamentals of titrimetric methods in analytical chemistry. This quiz covers key concepts such as titration, end points, and back-titration techniques. Test your knowledge and understanding of these critical analytical procedures.

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