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Cleaning Silverware – Electrochemical Reaction

  • Page ID
    128798
  • Required Training

    Required PPE

    UC Lab Safety Fundamentals

    Lab coat, safety glasses/goggles,

    nitrile gloves

    Equipment

    Chemicals

    Aluminum Foil

    100 mL H2O

    Silverware

    ~1 tsp NaCl

    Water heater

    15g/100mL sodium bicarbonate in vial

    Procedure:

    1. Plug in the water heater. Turn on switch (switch is below the handle). Add the vials of salt and sodium bicarb to the beaker. Slowly pour the boiling water to the beaker up to the mark on the tape (for the 100ml mark).
    2. Put the silverware in the container and make sure it is in contact with the aluminum foil, as it needs to create a complete circuit.
    3. Note the bubbles of CO2 escaping the surface of the most tarnished regions of the silverware and how the silver brightens as the aluminum tarnishes.

    Discussion:

    Aluminum has a lower ionization energy (energy required to remove electrons from an atom of the element) than silver. As a result, aluminum is oxidized (loses electrons and oxidation number increases), and silver is reduced (gains electrons and oxidation number reduced). Depending on the amount of tarnish, silver will be bright and the aluminum foil may be brown with tarnish (aluminum oxide) in a short while.

    *Note: The reaction can be done without baking soda, but it takes longer to see results.

    The baking soda (sodium bicarbonate) reacts with the sulfur-smelling H2S (tarnish):

    NaHCO3 (aq) + H2S (aq) → NaHS (aq) + H2O (l) + CO2 (g)

    The CO2 gas can be observed escaping from the most tarnished parts of the silver.

    The silver and aluminum must be in contact with each other because a small electric current flows between them during the reaction. This type of reaction involving an electric current (because atoms are charged), is called an electrochemical reaction, and is used in batteries to produce electricity. It converts the silver sulfide back to silver, without removing any silver.

    Tarnish in silverware is the combination of silver with sulfur containing substances in the air, not oxygen.

    Hazards:

    Caution on pouring hot water to prevent scalding

    SOP:

    N/A

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