Precipitation Reactions in Aqueous Solutions
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Questions and Answers

What is the correct way to write the precipitation equation for a reaction between silver nitrate and sodium sulfide?

  • 2Ag+ + 2NO3- + 2Na+ + S-- → Ag2S + 2Na+ + 2NO3-
  • AgNO3 + Na2S → Ag2S + NaNO3 (correct)
  • Ag+ + NO3- + Na+ + S-- → AgS + Na+ + NO3-
  • AgNO3 + Na2S → AgNO3 + Na2S

    • What is the purpose of predicting which products are dissolved in water or not in a precipitation equation?

  • To determine the solubility product constant (Ksp)
  • To write the equation in ionic form
  • To determine the molecular form of the expected product
  • To identify the insoluble compound(s) (correct)

    • What happens to the ionic form of the dissolved compound in a precipitation equation?

  • It is rewritten in molecular form
  • It is included in the final equation
  • It is excluded from the final equation (correct)
  • It is replaced with the molecular form of the product

    • What is the solubility product constant (Ksp) a measure of?

    <p>The level at which a solute dissolves in solution</p> Signup and view all the answers

    What is the correct way to write the ionic form of silver nitrate in a precipitation equation?

    <p>Ag+ + NO3-</p> Signup and view all the answers

    What is the purpose of writing a precipitation equation in ionic form for dissolved compounds?

    <p>To distinguish between dissolved and undissolved compounds</p> Signup and view all the answers

    What is the correct way to predict which products are dissolved in water or not in a precipitation equation?

    <p>By looking at the ionic form of the compounds</p> Signup and view all the answers

    What happens to the molecular form of the expected product in a precipitation equation?

    <p>It is included in the final equation</p> Signup and view all the answers

    What is the correct way to weigh a precipitation equation?

    <p>By balancing the equation</p> Signup and view all the answers

    What is the relationship between the solubility product constant (Ksp) and the solubility of a substance?

    <p>Higher Ksp values indicate higher solubility</p> Signup and view all the answers

    Study Notes

    Precipitation Reactions

    • Occur in aqueous solutions, resulting in an insoluble precipitate
    • Solubility rules:
      • All nitrate and acetate salts are dissolved in water
      • Most sulfate salts are dissolved in water, except for BaSO4, PbSO4, Hg2SO4, and CaSO4
      • Salts containing alkali metal ions (Li+, Na+, Cs+, and K+) are dissolved in water
      • All ammonium compounds (NH4) are dissolved in water
      • Halide ions (chloride, bromide, and iodide) dissolve in water, except for silver, lead, and mercury ions

    Insoluble Salts

    • All hydroxide compounds are insoluble, except for bonding with ammonium and barium ions and alkali metal ions
    • All carbonate, sulfite, chromate, and phosphate salts are insoluble, except for bonding with ammonium ions and alkali metal ions
    • All sulfide compounds are insoluble, except for bonding with ammonium ions and alkali metal ions

    Detection of End Point in Precipitation Reaction

    • Methods used to determine the end of the reaction: light scattering, electrodes, and indicators (Mohr's method, Volhard's method, Fajan's method)

    Mohr's Method

    • Utilizes chromate as an indicator
    • Chromate forms a precipitate with Ag+, but the precipitate has a greater solubility than AgCl
    • AgCl is formed first, and after all Cl- is consumed, the first drop of Ag+ in excess reacts with the chromate indicator, giving a reddish precipitate
    • Conditions: neutral medium (pH 7), as alkaline or acidic solutions can interfere with the reaction
    • Error: using a dilute chromate solution, which requires additional Ag+ for the Ag2CrO4 to form, leading to a late equivalent point; can be corrected by determining a blank

    Volhard's Method

    • Indirect method used for determining anions that precipitate with silver (e.g., Cl-, Br-, and I-)
    • Excess Ag+ is added to the unknown solution containing Fe3+ as an indicator

    Writing Precipitation Equations

    • Write the molecular form of the expected product in the precipitation equation
    • Predict which products are dissolved in water or not, and abbreviate accordingly
    • Write the equation in ionic form for soluble compounds only, and molecular form for insoluble compounds
    • Exclude the ionic form of the dissolved compound from the equation and balance the equation

    Solubility Product Constant (Ksp)

    • Represents the level at which a solute dissolves in solution
    • Higher Ksp value indicates higher solubility of a substance

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    Description

    Learn about precipitation reactions that occur in aqueous solutions, including the formation of insoluble precipitates and predicting the type of precipitate based on solubility rules.

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