Analyzing Cations and Anions in Chemistry
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Questions and Answers

What anion is present in the solution described in the content?

  • HCO3-
  • SO42- (correct)
  • CO32-
  • C2O42-

    • Ammonium ions (NH4+) are one of the cations present in the analysis of substance A.

    True (A)

    What color change is observed when the substance A is heated with anhydrous copper(II) sulfate?

    Blue

    The residue left after filtering substance A is suspected to contain ______.

    <p>Cu2+, Fe2+, Ni2+ or Cr2+</p> Signup and view all the answers

    Match the cations with their suspected colors based on the analysis of substance A:

    <p>Cu2+ = Blue solution Fe2+ = Green solution Ni2+ = Green solid Cr2+ = Yellow to green residue</p> Signup and view all the answers

    What color precipitate forms when Cu²⁺ is treated with 2M aqueous sodium hydroxide?

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

    A white precipitate formed from a cation indicates the presence of Zn²⁺ when using 2M aqueous ammonia.

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

    What happens to the color of the Co(OH)₂ precipitate over time?

    <p>It turns pink.</p> Signup and view all the answers

    The precipitate that forms from the reaction of Fe²⁺ with 2M aqueous hydroxide is __________.

    <p>Fe(OH)₂</p> Signup and view all the answers

    Match the following cations with the corresponding precipitates formed when treated with 2M aqueous sodium hydroxide:

    <p>Zn²⁺ = Zn(OH)₂ Cu²⁺ = Cu(OH)₂ Fe²⁺ = Fe(OH)₂ Fe³⁺ = Fe(OH)₃</p> Signup and view all the answers

    Which cation is indicated by a dirty green precipitate that turns brown on standing?

    <p>Fe²⁺ (D)</p> Signup and view all the answers

    Mn²⁺ produces a pink precipitate in the presence of excess ammonia.

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

    Which of the following observations indicates the presence of Fe2+ ions when adding sodium hydroxide solution?

    <p>Dirty green precipitate that dissolves in excess (B)</p> Signup and view all the answers

    Fe3+ ions can be confirmed by adding potassium thiocyanate solution.

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

    What color precipitate is formed when Cr3+ ions react with ammonia solution?

    <p>Grey-green precipitate</p> Signup and view all the answers

    The addition of sodium hydroxide solution results in a ________ precipitate indicating the presence of Fe3+.

    <p>reddish-brown</p> Signup and view all the answers

    Match the following ions with their corresponding color observations:

    <p>Fe2+ = Dirty green precipitate Fe3+ = Reddish-brown precipitate Cr3+ = Bluish-green precipitate Cu2+ = Blue precipitate</p> Signup and view all the answers

    What happens to the solution containing Fe2+ after adding H2O2?

    <p>It turns yellow (D)</p> Signup and view all the answers

    A yellow precipitate confirms the presence of Pb2+ ions in the solution.

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

    What is the likely color of the solution formed when Cr3+ is treated with excess NaOH?

    <p>Green solution</p> Signup and view all the answers

    The addition of potassium hexacyanoferrate (III) results in a ________ precipitate when Fe2+ ions are present.

    <p>deep blue</p> Signup and view all the answers

    Match the test with the corresponding ion it confirms:

    <p>Potassium thiocyanate = Fe3+ Ammonia in excess = Fe2+ Sodium hydroxide = Cr3+ Lead nitrate = Pb2+</p> Signup and view all the answers

    Flashcards

    Identifying Zn2+ with NaOH

    Adding sodium hydroxide (NaOH) dropwise to a solution containing zinc ions (Zn2+). A white precipitate (Zn(OH)2) forms, which dissolves in excess NaOH to form a colorless solution.

    Identifying Cu2+ with NaOH

    Adding sodium hydroxide (NaOH) dropwise to a solution containing copper ions (Cu2+). A pale blue precipitate (Cu(OH)2) forms, which does not dissolve in excess NaOH.

    Identifying Fe2+ with NaOH

    Adding sodium hydroxide (NaOH) to iron(II) ions (Fe2+). A dirty green precipitate (Fe(OH)2) forms. It turns brown on standing due to oxidation in air to iron(III) compounds.

    Identifying Fe3+ with NaOH

    Adding sodium hydroxide (NaOH) to iron(III) ions (Fe3+). A rust-brown precipitate (Fe(OH)3) forms. This precipitate is insoluble in excess NaOH.

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    Identifying Mn2+ with NaOH

    Adding sodium hydroxide (NaOH) to manganese(II) ions (Mn2+). A white precipitate (Mn(OH)2) forms. It rapidly turns brown due to oxidation in air to manganese(IV) compounds.

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    Identifying Cr3+ with NaOH

    Adding sodium hydroxide (NaOH) to chromium(III) ions (Cr3+). A green precipitate (Cr(OH)3) forms, which dissolves in excess NaOH to form a green solution.

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    Identifying Ni2+ with NaOH

    Adding sodium hydroxide to nickel(II) ions (Ni2+). A green precipitate (Ni(OH)2) forms. This precipitate is insoluble in excess sodium hydroxide.

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    Hydrated salt

    A salt that contains water molecules within its crystal structure.

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    Carbonate anion presence

    Presence of carbonate (CO32-), bicarbonate (HCO3-), or oxalate (C2O42-) is indicated by effervescence (release of gas), turning blue litmus red, and making limewater milky.

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    Cations suspected

    Based on tests, specific cations (metal ions) like Cu2+, Fe2+, Ni2+, Cr2+, or Cr3+ might be part of the substance.

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    Identifying Cr3+

    Adding dilute ammonia to a solution (often with excess ammonia) creates a recognizable color. This is followed by the addition of 1-butanol and dilute sulfuric acid to confirm a violet solution.

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    Qualitative analysis

    A set of tests used to identify and determine the composition of a matter by observing physical changes like color and gas generation.

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    Sodium Hydroxide test for cations

    A test for certain metal cations or ions (like Fe2+, Fe3+, Cr3+) in which a drop-wise addition of sodium hydroxide solution is used.

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    Ammonia solution test for cations

    A test for certain metal cations (like Fe2+, Fe3+, Cr3+) in a solution by adding ammonia solution drop-wise.

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    Potassium hexacyanoferrate(III) test

    A test for identifying iron(II) by adding a few drops of potassium hexacyanoferrate(III).

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    Potassium thiocyanate test

    A test for identifying iron(III), where potassium thiocyanate solution is added to a solution.

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    Fe2+ Confirmations

    Confirming the presence of Iron(II) by checking the reaction with H2O2; which forms a yellow solution.

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    Cr3+ confirm test

    A solution of Cr3+ with NaOH & H2O2, followed by adding lead nitrate.

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    Cation Identification summary

    A flowchart that summarizes common cation identification steps using chemical tests. These identify cations based on reactions like formation of precipitates or color changes.

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    Study Notes

    Anion and Cations

    • The text describes the analysis of substance A, which contains ammonium ions (NH₄⁺).
    • While the specific anion isn't explicitly stated, it can be inferred that the analysis involves identifying various cations.
    • The text mentions a white precipitate forming with Zn²⁺, indicating the presence of a specific anion that reacts with zinc to form a white precipitate.

    Color Observations

    • Heating substance A with anhydrous copper(II) sulfate causes a color change.
    • This suggests the presence of a substance within A that interacts with copper(II) sulfate, leading to a color change.
    • The residue left after filtering substance A is suspected to contain a specific compound, but the exact nature of the compound isn't specified.

    Reactions of Cations

    • Cu²⁺ with 2M aqueous sodium hydroxide forms a blue precipitate.
    • Zn²⁺ with 2M aqueous ammonia forms a white precipitate.
    • Co(OH)₂ precipitate changes color over time, indicating a transformation.
    • Fe²⁺ with 2M aqueous hydroxide forms a green precipitate.
    • Mn²⁺ in the presence of excess ammonia forms a pink precipitate.
    • A dirty green precipitate that turns brown on standing indicates the presence of Fe²⁺.
    • Fe³⁺ with potassium thiocyanate solution forms a red-brown color.
    • Cr³⁺ with ammonia solution forms a green precipitate.
    • Fe³⁺ with sodium hydroxide solution forms a brown precipitate.
    • Fe²⁺ with H₂O₂ forms a yellow-brown color.
    • Pb²⁺ in the solution forms a yellow precipitate.
    • Cr³⁺ with excess NaOH forms a green solution.
    • Fe²⁺ with potassium hexacyanoferrate (III) forms a blue precipitate.

    Key Takeaways

    • The text focuses on identifying cations using various reagents and observing the color changes of precipitates and solutions.
    • The specific anion involved is unclear, but its role is evident in the formation of precipitates with cations like Zn²⁺.
    • The analysis relies on the distinct color reactions of cations with specific reagents, such as sodium hydroxide, ammonia, and potassium thiocyanate.

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    Description

    This quiz focuses on the identification of various cations and anions present in a chemical analysis. Participants will answer questions related to color changes, precipitates, and reactions involving substances like ammonium ions and copper(II) sulfate. Test your knowledge on the chemistry of solutions and precipitation reactions!

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