Chemical Reactions with Dilute HCl
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Chemical Reactions with Dilute HCl

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Questions and Answers

What is the observed result of adding dilute HCl to thiosulfate in terms of gas liberation?

  • It generates sulfur dioxide gas and causes turbidity. (correct)
  • It liberates carbon dioxide gas.
  • There is no gas produced.
  • It produces oxygen gas.

    • Which of the following compounds is reacted with sulfur dioxide in a reaction that results in the bleaching of its color?

  • Potassium dichromate (correct)
  • Iodine (correct)
  • Bromine
  • Potassium permanganate (correct)

    • What change occurs to potassium persulfate upon boiling with water and how is the subsequent product detected?

  • Remains unchanged while releasing thermal energy.
  • Releases sulfur dioxide, detected by odor.
  • Forms sulfuric acid and detected by pH change.
  • Decomposes to produce oxygen, detected by blue KI-starch paper. (correct)

    • Which of the following statements correctly describes the behavior of sulfate ions when reacted with dilute HCl?

    <p>No reaction occurs.</p> Signup and view all the answers

    What is the main product formed from the reaction of calcium hydroxide and sulfur dioxide in the presence of water?

    <p>Calcium sulfite</p> Signup and view all the answers

    What will occur when bicarbonates are heated or when dilute ammonia is added to the filtrate containing bicarbonates?

    <p>Formation of carbonate from bicarbonate</p> Signup and view all the answers

    Which of the following ions would yield a white precipitate when mixed with BaCl2 or CaCl2 at cold temperatures?

    <p>Carbonate ion (CO32-)</p> Signup and view all the answers

    What indicates the presence of carbonates in a mixture when testing with dilute hydrochloric acid (HCl)?

    <p>Effervescence resulting in CO2 gas release</p> Signup and view all the answers

    When sulphates are tested with BaCl2, what would be the likely outcome?

    <p>No precipitate formation upon mixing</p> Signup and view all the answers

    In a reaction where a solution exhibits turbidity when passed through lime water, what can you infer about the solution?

    <p>The solution contains carbonates or bicarbonates.</p> Signup and view all the answers

    Study Notes

    Dry Reactions - Dilute HCl

    • Sulfide (S2-) - H2S gas is evolved when dilute HCl is added, both on cold and hot samples. - H2S can be detected by its rotten egg odor. - H2S can be detected by blackening of filter paper moistened with lead acetate, forming PbS. - H2S can be detected by yellowing of filter paper moistened with cadmium acetate, forming CdS.
    • Sulfite (SO32-) - SO2 gas is evolved when dilute HCl is added, due to the decomposition of unstable sulfurous acid.
      • SO2 can be detected by the burnt sulfur odor.
    • Thiosulfate (S2O32-) - No immediate change occurs on cold with dilute HCl.
      • Turbid solution forms on warming with dilute HCl or standing, due to the formation of colloidal sulfur and SO2 gas.
      • This is due to the decomposition of the liberated unstable H2S2O3.
    • Sulfate (SO42-) - No reaction occurs with dilute HCl.
    • Persulfates (S2O82-) - No effect on cold.
      • On boiling with water, persulfates decompose to give oxygen, catalyzed by Ag+.
      • This reaction produces ozone, detected by:
        • its characteristic odor.
        • turning KI-starch paper blue.

    Wet Reactions - Solubility and Precipitation

    • All Na+, K+ and NH4+ salts of sulfur are soluble in water, except:
      • Sulfides:
        • Other sulfides are insoluble except those of Ca2+, Ba2+, Sr2+ - these sulfides dissolve due to hydrolysis.
        • The precipitate is soluble in dilute acids.

    Analysis of Mixtures: Carbonates and Bicarbonates

    • To identify carbonates and bicarbonates in a mixture, add excess CaCl2, BaCl2 or MgSO4 on cold.
      • This results in a white precipitate of CaCO3 if carbonate is present, soluble in dilute acid
      • If the filtrate contains bicarbonate, boiling the solution or adding dilute ammonia will precipitate carbonate.

    Revision: Carbonates and Bicarbonates

    • Dry Reaction (Dil HCl) - both carbonates and bicarbonates produce effervescence due to the release of CO2.
      • Both carbonates and bicarbonates produce turbidity when the released CO2 is passed through lime water or baryta water.
    • Wet Reactions -
      • Carbonates produce a white precipitate on cold with BaCl2 (or MgCl2 or CaCl2).
      • Bicarbonates do not produce a precipitate on cold, but will produce a white precipitate on hot.

    Sulphur-Containing Anions

    • Sulfur-containing anions:
      • Sulfide (S2-)
      • Sulfite (SO32-)
      • Thiosulfate (S2O32-)
      • Sulfate (SO42-)
      • Persulfate (S2O82-)

    Analyzing Mixtures of S2-, SO32-, S2O32- and SO42-

    • Add CdCO3 to a solution containing the mixture of anions.
      • A yellow precipitate of CdS indicates the presence of sulfide (S2-).
      • Centrifuge and add BaCl2 to the filtrate:
        • A white precipitate indicates the presence of sulfate (SO42-) and sulfite (SO32-).
        • Add dilute HCl to the precipitate.
          • A white precipitate (BaSO4) remaining indicates sulfate (SO42-)
          • The filtrate contains sulfite (SO32-). Confirm with by oxidizing with Br2 or H2O2, which will form a white precipitate.
        • The filtrate contains thiosulfate (S2O32-). Heat the filtrate with dilute HCl.
          • The evolution of SO2 and the formation of a precipitate of sulfur confirm the presence of thiosulfate (S2O32-).

    Analyzing Mixtures of S2-, SO32- and S2O32-

    • Add CdCO3 to the solution
      • A yellow precipitate of CdS indicates the presence of sulfide (S2-).
      • Filter and add BaCl2 to the filtrate.
        • A white precipitate indicates the presence of sulfite (SO32-).
        • Heat the precipitate with dilute HCl.
          • The evolution of SO2 confirms the presence of sulfite (SO32-)
      • The filtrate contains thiosulfate (S2O32-). Confirm by oxidizing with Br2 or H2O2, which will form a white precipitate.

    Revision - Sulfur Containing Compounds

    • Dry reaction (Dil HCl)
      • Sulfide - H2S gas evolved, rotten egg odor, black with Pb acetate, yellow with Cd acetate.
        • Reducing properties.
      • Sulfite - SO2 gas evolved, burnt sulfur odor, turbidity with lime water or baryta water.
        • Reducing properties.
      • Thiosulfate - No immediate change on cold, on standing or heating: SO2 + S precipitate.
      • Sulfate - Negative.
      • Persulfate - Negative on cold, on boiling: [O] forms ozone with atmospheric oxygen, turns KI-starch paper blue.
    • Wet reaction
      • Sulfide - Negative. - Sulfite - White precipitate on cold, soluble in dilute acids.
        • On boiling with H2O2 the precipitate becomes insoluble. - Thiosulfate - Negative from dilute solutions, positive from concentrated solutions. - Sulfate - Positive. - Persulfate - Negative on cold, on boiling: White precipitate of Ba SO4.

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    Description

    Test your knowledge of dry reactions involving dilute hydrochloric acid. This quiz covers the behavior of sulfide, sulfite, thiosulfate, sulfate, and persulfates when mixed with dilute HCl, including the detection methods for each reaction. Learn about the gases evolved and their indicators through this engaging quiz.

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