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16.5: The Activity Series: Predicting Spontaneous Redox Reactions

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  • Page ID
    47584
  • Skills to Develop

    • Use the activity series to predict if a reaction will occur.

    We see below two metals that can be exposed to water. The picture on the left is of sodium, which gives a violent reaction when it comes in contact with water. The picture on the right is of silver, a metal so unreactive with water that it can be made into drinking vessels. 

    Figure \(\PageIndex{1}\): On the left, sodium reacts with water. On the right, silver in the form of cups do not react with water.

    The Activity Series

    Single-replacement reactions only occur when the element that is doing the replacing is more reactive than the element that is being replaced. Therefore, it is useful to have a list of elements in order of their relative reactivities. The activity series is a list of elements in decreasing order of their reactivity. Since metals replace other metals, while nonmetals replace other nonmetals, they each have a separate activity series. The table below is an activity series of most common metals and of the halogens.

    Table \(\PageIndex{1}\): Activity Series of Metals in Aqueous Solutions
    most active (easily oxidized – readily lose electrons))
    lithium Li

    These metals displace hydrogen from water Ca(s) + 2H2O(l)→ Ca(OH)2 + H2 (g) These elements are very reactive and react readily to form compounds

    potassium K
    barium Ba
    calcium Ca
    sodium Na

    These metals displace hydrogen from acids Zn(s) + HCl(aq)→ ZnCl2 + H2(g)
    magnesium Mg
    aluminum A
    zinc Zn
    chromium Cr
    iron Fe
    cadmium Cd
    nickel Ni
    tin Sn
    lead Pb

     
    hydrogen H  

     
    copper Cu These metals do not displace hydrogen from acids or water These elements are more stable, and form compounds less readily than do those higher in the table.
    silver Ag
    mercury Hg
    platinum Pt
    gold Au
    least active

    For a single-replacement reaction, a given element is capable of replacing an element that is below it in the activity series. This can be used to predict if a reaction will occur. Suppose that small pieces of the metal nickel were placed into two separate aqueous solutions: one of iron (III) nitrate and one of lead (II) nitrate. Looking at the activity series, we see that nickel is below iron, but above lead. Therefore, the nickel metal will be capable of replacing the lead in a reaction, but will not be capable of replacing iron.

    \[\ce{Ni} \left( s \right) + \ce{Pb(NO_3)_2} \left( aq \right) \rightarrow \ce{Ni(NO_3)_2} \left( aq \right) + \ce{Pb} \left( s \right)\]

    \[\ce{Ni} \left( s \right) + \ce{Fe(NO_3)_3} \left( aq \right) \rightarrow \text{NR (no reaction)}\]

    In the descriptions that accompany the activity series of metals, a given metal is also capable of undergoing the reactions described below that section. For example, lithium will react with cold water, replacing hydrogen. It will also react with steam and with acids, since that requires a lower degree of reactivity.

     

    Steps for Problem Solving

    Example \(\PageIndex{1}\)

    Use the activity series to predict if the reaction below will occur. If not, write \(\text{NR}\). If the reaction does occur, write the products of the reaction and balance the equation.

    \(\ce{Al} \left( s \right) + \ce{Zn(NO_3)_2} \left( aq \right) \rightarrow\)

    Example \(\PageIndex{2}\)

    Use the activity series to predict if the reaction below will occur. If not, write \(\text{NR}\). If the reaction does occur, write the products of the reaction and balance the equation.

    \(\ce{Ag} \left( s \right) + \ce{HCl} \left( aq \right) \rightarrow\)

    Plan the problem.  Compare the placements of aluminum (the element doing the replacing) and zinc (the element being replaced) on the activity series. Compare the placements of silver (the element doing the replacing) and hydrogen (the element being replaced) on the activity series.
    Solve

    Since aluminum is above zinc, it is capable of replacing it and a reaction will occur. The products of the reaction will be aqueous aluminum nitrate and solid zinc. Take care to write the correct formulas for the products before balancing the equation. Aluminum adopts a \(+3\) charge in an ionic compound, so the formula for aluminum nitrate is \(\ce{Al(NO_3)_3}\). The balanced equation is:

    \[2 \ce{Al} \left( s \right) + 3 \ce{Zn(NO_3)_2} \left( aq \right) \rightarrow 2 \ce{Al(NO_3)_3} \left( aq \right) + 3 \ce{Zn} \left( s \right)\]

    Since silver is below hydrogen, it is not capable of replacing hydrogen in a reaction with an acid.

    \[\ce{Ag} \left( s \right) + \ce{HCl} \left( aq \right) \rightarrow \text{NR}\]

    Exercise \(\PageIndex{1}\)

    Use the activity series to predict if the following reactions will occur. If not, write \(\text{NR}\). If the reaction does occur, write the products of the reaction and balance the equation.

    a. Would it be possible to store a silver spoon in a zinc nitrate solution? That is, will the following reaction occur:

    \Ag_{(s)} + Zn(NO_3)_{2 (aq)} → 

    b. Would it be possible to store a silver nitrate solution in a copper container? That is, will the following reaction occur:

    \[Cu_{(s)} + AgNO_{3 (aq)} → 

    Summary

    • Metals and halogens are ranked according to their ability to displace other metals or halogens below them in the series.

    Contributors

    • CK-12 Foundation by Sharon Bewick, Richard Parsons, Therese Forsythe, Shonna Robinson, and Jean Dupon.