The reactivity series of metals

Although they are separated out in this chapter, the teaching of redox reactions is likely to be intertwined with the reactivity series of metals (section 7.3) and work on the extraction of metals (section 7.4). This is because all these reactions are redox reactions, as are the combustion reactions met earlier. 

By the age of 14 students should have some experience of combustion reactions and reactions with oxygen. They should know the term oxidation. The reactivity series of metals may have been covered by this stage too. 

Although carbon is not a metal, it is very useful to see if it can be fitted into the reactivity series of metals. A class experiment (page 242) and a teacher demonstration (page 243) demonstrate where it goes. 

Zinc metal reacts spontaneously with an aqueous solution of copper sulfate when they re placed in direct contact. Zinc, being a more reactive metal than copper (it s higher on the activity series of metals presented in Chapter 8), displaces the copper ions in solution. The displaced copper deposits itself as pure copper metal on the surface of the dissolving zinc strip. At first, the reaction may appecir to be a simple single replacement reaction, but it s also a redox reaction. 

Using your an ox and red cat mnemonics, you know that the anode is the site of aluminum (Al) oxidation, while the cathode is the site of tin (Sn) reduction. This idea is also apparent from the activity series of metals (see Chapter 8), which shows that aluminum is far more reactive than tin. 

The ways in which metal nitrates, carbonates, oxides and hydroxides decompose can also be discussed in terms of the reactivity series of the metals. The decomposition processes are different, depending on the position of the metal in the reactivity series. 

This is also a redox reaction involving the transfer of two electrons from the zinc metal to the copper ions. The zinc is oxidised to zinc ions in aqueous solution, while the copper ions are reduced. (See Chapter 5, p. 73, for a discussion of oxidation and reduction in terms of electron transfer.) It is possible to confirm the reactivity series for metals using competition reactions of the types discussed in this section. 

Reactivity series of metals An order of reactivity, giving the most reactive metal first, based on results from experiments with oxygen, water and dilute hydrochloric acid. 

Zinc is a more reactive metal than copper, so when corrosion occurs, the zinc preferentially reacts. Zinc is above hydrogen in the Activity Series of Metals copper is below hydrogen. 

Table 16.1 shows the activity series of metals. This table lists metals in order of decreasing tendency to lose electrons. The metals at the top of the list have the greatest tendency to lose electrons—they are most easily oxidized and therefore the most reactive. The metals at the bottom of the list have the lowest tendency to lose electrons—they are the most difficult to oxidize and therefore the least reac-... 

Electrolysis is the decomposition of a compound into its elements by an electric current. It is often used to extract metals that are high in the reactivity series. These metals cannot be extracted by heating their ores with carbon. Electrolysis is also used to produce non-metals such as chlorine and to purify some metals. Electrolysis is generally carried out in an electrolysis cell (Figure 20.2). 

This belongs to the second series of the transition metals. So far as reactivity is concerned, this series is very similar to the first and especially the third. Thus, zirconium and hafnium are so similar that it is very difficult to separate them (except for nuclear purposes where the presence of the second is harmful). The same goes for tantalum and niobium. There are two main differences between the three series within each group. 

A comparison of this equation with the equations provided above points out that lead (IV) oxide is clearly not a base. The nature of metallic hydroxides varies according to the position of the metal in the reactivity series, as given in Table 6.3. Metallic hydroxides are electrovalent compounds, composed of metal ions, which are positively charged, and hydroxy ions, OTT. The number of OTT ions associated with one metallic ion is equal to the valency of the metal, e.g., Na+OH sodium is monovalent Ca2+(OTT)2 calcium is divalent. The metallic hydroxides form a very important series of compounds, and are known to have many uses both in the laboratory and in industry. 

Berkelium is a metallic element located in group 11 (IB) of the transuranic subseries of the actinide series. Berkelium is located just below the rare-earth metal terbium in the lanthanide series of the periodic table. Therefore, it has many chemical and physical properties similar to terbium ( Tb). Its isotopes are very reactive and are not found in nature. Only small amounts have been artificially produced in particle accelerators and by alpha and beta decay. 

In listing the ways in which metal ions may promote organic reactions, the requirement that the metal ion be suitably positioned within the substrate molecule was emphasized. Specific complexation or chelation of the metal ion with the substrate appears to be an absolute requirement of metal ion catalysis. In many cases chelation appears to be the rule, which usually means that the substrate must contain a donor atom in addition to the reactive center of the molecule with which the metal ion also complexes, or must contain two donor atoms in addition to the reactive center. Many attempts have been made to correlate the effectiveness of catalysis by a series of metal ions with the relative formation constants of the complexes. Such correlations have been successful in a number of reactions, but unsuccessful in others. In the successful correlations the complex chosen for the correlation closely approximates the transition state of the reaction. This indicates that the metal ion complex must stabilize the transition state of the reaction in order to assist the reaction effectively, and that metal ion complex formation in the ground state can have an effect exactly opposite to that of catalysis, since in such a case the ground state becomes stabilized. 

Describe how simple chemical cells can be used to confirm the order of reactivity of the metals in the reactivity series. 

Give a use for each of the other unreactive metals shown in the reactivity series. 

The reactivity series is useful for predicting how metals will react. It can also be used to predict the reactions of some metal compounds. The tables on... 

A more reactive metal has a greater tendency to form a metal ion by losing electrons than a less reactive metal does. Therefore, if a more reactive metal is heated with the oxide of a less reactive metal, then it will remove the oxygen from it (as the oxide anion). You can see from the reactivity series that iron is less reactive than aluminium (p. 150). If iron(m) oxide is mixed with aluminium and the mixture is heated using a magnesium fuse (Figure 10.6), a very violent reaction occurs as the competition between the aluminium and the iron for the oxygen takes place. 

In another reaction, metals compete with each other for other anions. This type of reaction is known as a displacement reaction. As in the previous type of competitive reaction, the reactivity series can be used to predict which of the metals will win . 

In a displacement reaction, a more reactive metal will displace a less reactive metal from a solution of its salt. Zinc is above copper in the reactivity series. 

Over the centuries other metals, which like iron are also relatively low in the reactivity series, were isolated in a similar manner. These included copper, lead, tin and zinc. However, due to the relatively low abundance of the ores containing these metals, they were not extracted and used in large amounts. 

Targe lumps of the ore are first crushed and ground up by very heavy machinery. Some ores are already fairly concentrated when mined. For example, in some parts of the world, haematite contains over 80% Fe2Os. However, other ores, such as copper pyrites, are often found to be less concentrated, with only 1% or less of the copper compound, and so they have to be concentrated before the metal can be extracted. The method used to extract the metal from its ore depends on the position of the metal in the reactivity series. 

Metals towards the middle of the reactivity series, such as iron and zinc, may be extracted by reducing the metal oxide with the non-metal carbon. 

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