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Oxidation States of Manganese

  • Page ID
    131419
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    Required Training

    Required PPE

    UC Lab Safety Fundamentals

    Lab coat, safety glasses/goggles, nitrile gloves

    Equipment

    Chemicals

    Four 50 mL beakers

    60 mL 0.01M KMnO4

    White sheet of paper

    4 mL 3M H2SO4

    60 mL 0.02M NaHSO3

    6 mL 2M NaOH

    Procedure:

    1. Place 15 mL of 0.01M KMnO4 solution onto each of the four 50 mL beakers labeled A, B, C, and D. Set the beakers on a white sheet of paper to enhance visibility.
    2. Set beaker D aside as a reference; it is the +7 oxidation state of Mn (purple)
    3. In beaker A, add 4 mL of 3M H2SO­4 (acidic condition). With stirring, slowly add ~32 mL of 0.02M NaHSO3. Note the change from purple to colorless. This is the +2 state of Mn

    2MnO4- (aq) + H+ (aq) + 5HSO3- (aq) ↔ 2Mn2+ (aq) + 5SO42- (aq) + 3H2O (l)

    4) In beaker B, add 6 mL of 2M NaOH (basic condition). With stirring, slowly add ~8 mL 0.02M NaHSO3. Note the color change from purple to green. This is the +6 state of Mn.

    2MnO4- (aq) + 3OH- (aq) + HSO3- (aq)­ ↔ 2MnO42- (aq) + SO42- (aq) + 2H2O (l)

    5) With stirring, slowly add ~20 mL 0.02M NaHSO3 to beaker C (neutral condition). Note the formation of a brown precipitate, indicating the +4 state of Mn.

    OH- + 2MnO4- (aq) + 3HSO3- (aq) ↔ 2MnO2 (s) + 3SO42- (aq) + 2H2O (l)

    Hazards:

    Potassium permanganate is a strong oxidizer, so keep it away from any reducing agent. KMnO4 will also stain skin. Sulfuric acid and sodium hydroxide can cause severe burns. In case of skin contact, wash with copious water.

    SOP: clipboard_ed4a8fb6c6526068c105738977a28fce4.png

    Corrosive – Sodium Hydroxide, Sulfuric Acid,

    Oxidizer – Potassium Permanganate

    Disposal (by Storeroom)

    The objective is to convert all the manganese compounds to Mn(II) and discard it down the sink. Fill a 1L plastic container with 200 mL tap water. Add the contents of each beaker to this container one at a time. Acidify the solution with 1M HCl if needed. Add 2% NaHSO3 in small portions, with stirring, until all the brown manganese dioxide is reduced (solution turns clear). Neutralize and flush down the sink with plenty of water (at least 10X the total volume of solution).


    Oxidation States of Manganese is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by LibreTexts.

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