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    Chemistry Problem Set: Half-Reactions

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    2. Which half-reactions represent oxidation and which reduction? Explain your reasoning.
    2+ -
    a. Fe --> Fe + 2 e

    4+ _ 2+
    b. Ni + 2 e --> Ni

    - -
    c. 2 H O + 2 e --> H + 2 OH
    2 2

    4. Explain the difference between a rechargeable battery and one that must be discarded. Contrast a NiCad battery with an alkaline battery in your explanation.

    7. Two common units associated with electricity are volts and amps. What does each unit measure?

    14. What is the difference between a storage battery and a fuel cell?

    3. Some people object to synthetic polymers, saying that polymers are not "natural." Give example of two natural polymers.

    12. This is a representation of a small segment of polyethylene. The hydrogen atoms are omitted for the sake of clarity.
    I I I I
    I I I I
    I I I I
    I I I I
    I I I I
    I I I I
    I I I I

    Does this representation predict that the carbon-to-carbon-to-carbon bond angles in polyethylene are all 180 degrees? Explain your reasoning.

    19. The structure for the styrene monomer:

    H H
    C == C
    H (a pentagon with a circle inscribed in the middle)

    a. Rewrite this shorthand structure showing all of the atoms.
    b. What is the molecular formula for styrene?
    c. What is the molar mass of a polystyrene molecule consisting of 5000 monomer units?

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    Solution Preview

    See the attached file.
    2. A reaction which occurs by the loss of electrons is known as an oxidation reaction and a reaction in which electrons are accepted is called a reduction reaction.
    a. Loss of an electron occurs and it is an Oxidation Reaction
    b. Here Ni accepts two electrons thus getting reduced to Ni2+ : A reduction reaction
    c. Here H+ accepts electrons and gets reduced to Hydrogen, hence a reduction reaction

    4. Although there are many different types, batteries are generally divided into two types?primary and secondary. Primary batteries are used once and thrown away. Secondary batteries can be recharged and used again. Generally speaking, alkaline batteries are primary batteries. Rechargeable batteries contain reversible chemical materials, allowing them to be recharged again and again.

    Alkaline batteries were not designed to meet the ...

    Solution Summary

    Solution is 800 words and includes an illustration of the molecular formula for styrene in the attachment.