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Reducing agent

    A reducing agent is the element or a compound in a redox (reduction-oxidation) reaction (see electrochemistry) that reduces another species In doing so, it becomes oxidized and is therefore the electron donor in the redox For example consider the following reaction:
    2Mg(s) + O2 --> 2Mg2+(s) + 2O2-
    The reducing agent in this reaction is Magnesium Magnesium donated its two valence electrons has become an ion and allows itself as well as oxygen to become stable
    Reducing agents need to be protected from air because they react with oxygen

    What makes a strong Reducing Agent?

    Since the job of a reducing agent is to donate electrons then it makes sense to say that a strong reducing agent is one which loses or donates electrons easily The nucleus in an atom is the main force pulling the electrons inwards keeping them from going anywhere Thus if the atomic radius is large the influence of the nucleus is not sufficient Elements with large atomic radii are stronger reducing agents since no significant force keeps them from releasing electrons easily Also elements that have a low electronegativity “the ability of an atom or molecule to attract electrons”1 and relatively small ionization energies serve as good reducing agents too ( see electronegativity ). "The measure of a material to oxidize or lose electrons is known as its oxidation potential"2 The table below shows a few reduction potentials that could easily be changed to oxidation potential by simply changing the sign Reducing agents can be ranked by increasing strength by ranking their oxidation potentials The reducing agent will be the strongest when it has a more positive oxidation potential and will be a weak reducing agent whenever it has a negative oxidation potential The following table provides the reduction potentials of the indicated reducing agent at 25° C
    Oxidizing AgentReducing AgentReduction Potential (v)
    Li+ + e- =Li-304
    Na+ + e- =Na-271
    Mg+2 + 2e- =Mg-238
    Al+3 + 3e- =Al-166
    2H2O(l) + 2e- = H2(g) + 2OH - -083
    Cr+3 + 3e- =Cr-074
    Fe+2 + 2e- =Fe-041
    2H+ + e- =H2000
    Sn+4 + 2e- =Sn+2+015
    Cu+2 + e- =Cu++016
    Ag+ + e- =Ag+080
    Br2 + 2e- =2Br-+107
    Cl2 + 2e- =2Cl-+136
    MnO4-2 + 8H+ + 5e- =Mn+2 + 4H2O+149

    In order to tell which is the strongest reducing agent change the sign of its respective reduction potential in order to make it oxidation potential The bigger the number the stronger a reducing agent it is.
    For example if you were to list Cu, Cl- Na and Cr in order you get their reduction potential change the sign to make it oxidation potential and list them from greatest to least You well get Na, Cr, Cu and Cl-; Na being the strongest reducing agent and Cl- being the weakest one
    A few good common reducing agents include active metals such as potassium calcium barium sodium and magnesium and also compounds that contain the H- ion those being NaH LiAlH4 and CaH2
    Also some elements and compounds can be both reducing or oxidizing agents Hydrogen gas is a reducing agent when it reacts with non-metals and an oxidizing agent when it reacts with metals( see oxidizing agent )
    2Li(s) + H2(g) -->2LiH(s) acts as a reducing agent
    H2(g) + F2(g) --> 2HF(g) acts as a oxidizing agent

    The Importance of Reducing and Oxidizing Agents

    Reducing agents and Oxidizing agents are the ones responsible for corrosion which is the “degradation of metals as a result of electrochemical activity”3 ( see corrosion ). Corrosion requires an anode and cathode to take place The anode is an element that loses electrons (reducing agent) thus oxidation always occurs in the anode and the cathode is an element that gains electrons (oxidizing agent) thus reduction always occurs in the cathode Corrosion occurs whenever there’s a difference in oxidation potential When this is present the anode metal will begin deteriorating given that there is an electrical connection and the presence of an electrolyte ( see electrolyte )

    Common reducing agents

    • Ferrous ion
    • Lithium aluminum hydride (LiAlH4)
    • Nascent hydrogen
    • Potassium ferricyanide (K3Fe(CN)6)
    • Sodium amalgam
    • Sodium borohydride (NaBH4)
    • Stannous ion
    • Sulfite compounds
    • Hydrazine (Wolff-Kishner reaction)
    • Zinc-mercury amalgam (Zn(Hg)) (Clemmensen reduction)
    • Diisobutylaluminum hydride (DIBAH)
    • Lindlar catalyst
    • Oxalic acid (C2H2O4)

    Common reducing agents and their products

    AgentProduct
    H2 HydrogenH+ H2O
    metalsmetal ions
    CCO2 carbon dioxide
    hydrocarbonsCO2 carbon dioxide H2O

    See also


    External links


    Sources

    23wwwsemiconfareastcom/oxpotentialhtm
    wwwchemedchempurdueedu/genchem/topicreview/bp/ch19/oxred_3html
    wwwmembersaolcom/logan20/agentshtml
    "Chemical Principles: The Quest for Insight" Third Edition Peter Atkins and Loretta Jones pg. F76
    1http://enwikipediaorg/wiki/Electronegativity