Series activity

The tendency for a species to become oxidized or reduced determines the sign and potential of the half-cell. The tendency is strongly related to the chanical reactivity of the species concerned in aqueous systems. Based on the potential developed in a half-ceU nnder controlled conditions, the elements may be arranged in an order known as the activity series or electromotive series (Table 15.1). In general, the metals at the top of the activity series are most chemically reactive and tend to give up electrons easily, following the reaction M M + e. The metals at the bottom of the series are more noble and therefore less active. They do not give up electrons easily in fact, their cations will accept electrons from metals above them in the activity series. In the process, the cations become neutral metal atoms and plate out of solution, while the more active metals become ionic and dissolve. This is illustrated as follows  

Metal A (active) — metal ion A. +e Metal ion (noble) -t e — metal B 

In short, the more active metals displace the less active metals from solution. As an example, if an iron strip is immersed in a solution of copper sulfate, some of the iron dissolves, forming iron ions, while the copper ions become metalhc and copper metal plates out on the remaining iron strip. The activity series can be used to predict displacement reactions between atoms and ions in compounds of the type A H- BC AC H- B, where A and B are atoms. Using the activity series, any atom A will displace from a compound any element B listed below it, but will not displace any element listed above it 

05 These metals displace hydrogen from acids and dissolve in all acids, including water. 

37 These metals react with acids or steam. 

28 These metals react slowly with all acids 

32 These metals react with oxidizing acids (e.g., HNO3) 

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Identify students prior knowledge about the metal activity series. 

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 ... 

The reactivity of a substance depends on its ability to gain or lose electrons. It is possible to arrange the elements into a series based upon their reactivity. Such a list is called an activity series. 

In this activity, you will use a few metals, their compounds, and dilute hydrochloric acid to show single-replacement reactions and construct an activity series. 

How can the results of these reactions be used to form an activity series ... 

Read the entire laboratory activity. Form a hypothesis about how an activity series can be formulated. Record your hypothesis in the next column. 

Drawing a Conclusion Cite the experimental evidence used to establish the location of hydrogen in this activity series. 

Compare your activity series to one in a textbook or reference book. 

Fig. 15. Mixed copolymers were generated to examine the effect of changing the recognition epitope density for a biologically active series of carbohydrate-substituted polymers. Note n and m represent ratios of mannose and galactose residues, respectively.

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. 

Table 6.1 Activity Series of Metals in Aqueous Solution...

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