The Activity Series

Can we predict whether a certain metal will be oxidized either by an acid or by a particular salt This question is of practical importance as well as chemical interest. According to Equation 4.27, for example, it would be unwise to store a solution of nickel nitrate in an iron container because the solution would dissolve the container. When a metal is oxidized, it forms various compounds. Extensive oxidation can lead to the failure of metal machinery parts or the deterioration of metal structures. 

Different metals vary in the ease with which they are oxidized. Zn is oxidized by aqueous solutions of Cu, for example, but Ag is not. Zn, therefore, loses electrons more readily than Ag that is, Zn is easier to oxidize than Ag. 

A list of metals arranged in order of decreasing ease of oxidation, such as TABLE 4.5, is called an activity series. The metals at the top of the table, such as the alkali metals and the alkaline earth metals, are most easily oxidized that is, they react most readily to form compounds. They are called the active metals. The metals at the bottom of the activity series, such as the transition elements from groups 8B and IB, are very stable and form compounds less readily. These metals, dlich are used to make coins and jewelry, are called noble metals because of their low reactivity. 

The activity series can be used to predict the outcome of reactions between metals and either metal salts or acids. Any metal on the list can be oxidized by the ions of elements below it. For example, copper is above silver in the series. Thus, copper metal is oxidized by silver ions  

TABLE 4.5 Activity Series of Metals in Aqueous Solution 

Does a reaction occur (a) when an aqueous solution of NiCl2(a(7) is added to a test tube containing strips of mefallic zinc, and (b) when NiCl2(ac7) is added to a test tube containing Zn(N03)2(a 7)  

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A metal will transfer electrons to any cation that is lower on the list. Furthermore, the list is in order of reactivity, so the greater the separation between the species, the more vigorous the reaction. Example shows how to use the activity series to predict the outcome of a metal displacement reaction. 

A displacement reaction occurs when a metal high in the activity series is added to a solution containing a cation lower on the list. For each case, we need to identify the species in the mixture and evaluate reactivity using the activity series. 

In everyday life, we encounter silver as an unreactive solid that is used for jewelry, and we know that iron, while it msts, is relatively stable. Calcium and magnesium, in contrast, are not normally encountered as pure metals but instead as salts. Thus, the directions of the reactions predicted by the activity series are in accord with everyday observations. 

When several properties are combined or when compounds belong to the lower members of the active series, the molecule becomes particularly dangerous. 

The diagram shows the activity series of some metals (left) and nonmetals (right). A student set up four beakers, each containing 100 mL of dilute hydrochloric acid (HCl[aq]). She added 5 g of a metal to each beaker in this order aluminum (Al), copper (Cu), sodium (Na), and zinc (Zn). Which metal will NOT react with the acid ... 

Notice that E°ei for silver is lower than E°ied for gold. This means that because silver is higher in the activity series, silver metal will reduce the gold ion. 

Reduction always occurs at the cathode. Note that H°ed for silver is +0.7991 volt, according to the Table of Standard Reduction Potentials. E°ed for copper is +0.337. This means that the copper metal is higher in the activity series than the silver metal, so copper metal will reduce the silver ion. The equation that describes reduction (or the cathode reaction) is therefore... 

Oxidation occurs at the anode. Silver is lower in the activity series than copper. Therefore, the oxidation half-reaction is... 

We may predict many redox reactions of metals by using an activity series. An activity series lists reactions showing how various metals and hydrogen oxidize in aqueous solution. Elements at the top of the series are more reactive (active) than elements below. A reaction occurs when an element interacts with a cation of an element lower in the series. The more active elements have a stronger tendency to oxidize than the less active elements. The less active elements tend to reduce instead of oxidize. The reduction reactions are the reverse of the oxidation reactions given in the activity series table, Table 4-1. This is an abbreviated table. Refer to your textbook for a more complete table. 

We may use the activity series to predict certain types of redox reactions. For example, suppose you wanted to write the equation between magnesium metal and hydrochloric acid ... 

Hydrochloric acid is a strong acid (strong electrolyte). Therefore, the species present would be Mg(s), H+(aq), and Cl (aq). Locate the element (Mg) and the cation (H+) in the activity series. 

In order for there to be a reaction between the two, the element must be above the cation in the activity series. Since Mg is higher on the table, it will oxidize (react as shown in the table). (Note only Mg, not Mg2+, undergoes oxidation.) If a substance undergoes oxidation then something must also undergo reduction. In this problem, the only option for a reduction species is the H+. The reduction is the reverse of the equation in the table. 

The anions, negative ions, are not of concern to us at this time. We only need to locate the elements and cations on the activity series table. Here is our abbreviated activity series table with the substances from the first reaction in boldface ... 

There will be no reaction because the substance on the left is not higher on the activity series. 

Using the activity series in this text, write net ionic equations for each of the following. Indicate no reaction, NR, where appropriate. 

The standard cell potential for the reduction of hydrogen ions to hydrogen gas is, by definition, 0.00 V. This potential is for the standard hydrogen electrode, SHE, which is the reference to which we compare all other cell potentials. All metals above hydrogen on the Activity Series will displace hydrogen gas from acids. (See Chapter 4) Metals below hydrogen will not displace hydrogen gas. 

Metals above hydrogen on the Activity Series will displace hydrogen gas from acids. When this happens, the metal undergoes oxidation. Metals below hydrogen will not release hydrogen from acid solutions. 

Metals above hydrogen on the Activity Series react with acids to produce what gas ... 

For the first two types, a table of metals relating their ease of oxidation to each other is useful in being able to predict what displaces what. Table 6.1 shows the activity series for metals, which lists the metal and its oxidation in order of decreasing ease of oxidation. An alternative to the activity series is a table of half-cell potentials, as discussed in Chapter 16. In general, the more active the metal, the lower its potential. 

If a piece of copper metal was placed in a solution of SrfNOj aq) there would be no reaction, since copper is lower than tin on the activity series. This table allows us to also predict that if sodium metal is placed in water, it will displace hydrogen, forming hydrogen gas ... 

The copper is below hydrogen on the activity series, so H2 cannot be formed by this acid-metal reaction. Nitric acid is an oxidizing agent, which will oxidize copper to Cu2+ giving Cu(N03)2. 

Know how to use the activity series to predict whether or not an element will displace another element. 

Some metals are more reactive than others. By comparing how different metals react with the same ions in aqueous solutions, an activity series for the tested metals can be developed. The activity series will reflect the relative reactivity of the tested metals. It can be used to predict whether reactions will occur. 

Comparing and Contrasting Compare your activity series with the activity series shown here. How does the order you determined for the four metals you tested compare with the order of these metals ... 

If the activity series you sequenced does not agree with the order in the... 

The metal activity series is shown in the table helow. The more reactive metals are near the top of the series, and the less reactive metals are near the bottom. In this investigation, you will relate the activity series to the ease with which metals are oxidized and metal ions are reduced. 

How is the order of the metals in the activity series related to the ease with which metals are oxidized and metal ions are reduced ... 

Which list from questions 4 and 5 puts the metals in the same order as they appear in the activity series ... 

Use the activity series to choose a reducing agent that will reduce aqueous nickel(II) ions to metallic nickel. Explain your reasoning. 

Aqueous solutions of alkali hydroxides do not attack cadmium. Cadmium replaces elements that are less electropositive in the activity series from their salt solutions. The standard electrode potential ... 

A) Any element higher in the activity series will react with the ion of any element lower in the activity series. 

A term used to describe how easily a metal is oxidized is active. A more active metal is one that is more easily oxidized. A listing of metals in order of activity is known as an activity series. The activity series is used to determine which substances will be oxidized and reduced in an electrochemical cell the element higher on the list will be oxidized. For example, in a cell with aluminum and silver electrodes in their appropriate solutions, aluminum is oxidized and silver is reduced. Therefore, aluminum is the anode and silver is the cathode. If you have ever bitten a piece of aluminum foil and experienced discomfort, you had this electrochemical process occur in your mouth. Silver (or mercury) fillings and the aluminum serve as electrodes and your saliva serves as an electrolyte between the two. The resulting current stimulates the nerves in your mouth resulting in the discomfort. 

Single replacement reactions in which metals replace other metals cire especially common. Not all single replacement reactions occur as written, though. You sometimes need to refer to a chart called the activity series to determine whether such a reaction will take place. 

Table 8-2 presents the activity series. To determine whether a single replacement reaction will occur, compare the two metals in the reaction ... 

If the metal that is single and not bonded is higher on the activity series than the metal that is bonded in the compound, the reaction will take place. 

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