Hydrogen activity series

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

A series of papers by Shustorovi ch(63) and/or Baetzo1d(64) summarized in a recent article(65) have addressed the problem of chemisorption on metal surfaces in terms of electron accepting and donating interactions. Saillard and Hoffmann (66) developed qualitatively identical pictures of these interactions but starting from fragment orbital type analysis. These papers are only a few of the theoretical discussions that consider hydrogen activation, however we will use their approach because it address the problem in a fashion that can interpolate between the organometallic cluster and the bulk. 

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. 

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 ... 

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. 

ACTIVITY SERIES- Also referred to as the electromotive series or the displacement series, this is an arrangement of the metals (other elements can be included) in the order of their tendency to react with water and acids, so that each metal displaces from solution those below itiu the series and is displaced by those above it. See Table 1. Since the electrode potential of a metal in equilibrium with a solution of its ions cannot be measured directly, the values in the activity series are, in each case, the difference between the electrode potential of the given metal tor element) in equilibrium with a solution of its ions, and that of hydrogen in equilibrium with a solution of its ions. Thus in the table, it will be noted that hydrogen lias a value of 0.000. In experimental procedure, the hydrogen electrode is used as the standard with which the electrode potentials of other substances are compared. The theory of displacement plays a major role in electrochemistry and corrosion engineering. See also Corrosion and Electrochemistry. 

The position of hydrogen in the activity series is particularly important because it indicates which metals react with aqueous acid (H + ) to release H2 gas. The metals at the top of the series—the alkali metals of group 1A and alkaline earth metals of group 2A—are such powerful reducing agents that they react even with pure water, in which the concentration of H+ is very low ... 

The oxidizing properties of sulfuric acid depend on its concentration and temperature. In dilute solutions at room temperature, H2S04 behaves like HC1, oxidizing metals that stand above hydrogen in the activity series (Table 4.3, page 132) ... 

But if a chemist placed metallic silver into hydrochloric acid, nothing would happen. That is because silver is not as reactive as hydrogen. It is below hydrogen in the activity series and it cannot replace the hydrogen in the reaction ... 

This diagram has special relevance to electrochemical corrosion (see page 32.) Thus metals above H2 in activity series will tend to undergo oxidation (corrosion) by reducing H+ ions or water. The unity partial pressures are of course purely arbitrary criteria in a system open to the atmosphere, water can decompose even at much lower hydrogen partial pressures. 

Recently, a nickel zeolite hydrogenation catalyst has been prepared by a novel route (94) involving the adsorption and decomposition of nickel carbonyl onto NaX, which would not be expected to result in the formation of acid sites. In general, the platinum metal-containing zeolites are more active than those containing other transition metals. For example, in zeolite Y the following activity series has been found,... 

Through experimentation, chemists have ranked the relative reactivity of the metals, including hydrogen (in acids and in water), in an activity series. The reactive metals, such as potassium, are at the top of the activity series. The unreactive metals, such as gold, are at the bottom. In Investigation 4-A, you will develop an activity series using single displacement reactions. 

As you can see in Table 4.2, the more reactive metals are at the top of the activity series. The less reactive metals are at the bottom. A reactive metal will displace or replace any metal in a compound that is below it in the activity series. Metals from lithium to sodium will displace hydrogen as a gas from water. Metals from magnesium to lead will displace hydrogen as a gas only from acids. Copper, mercury, silver, and gold will not displace hydrogen from acids. 

When a metal is placed in water, the reactivity information in the activity series helps you tell if hydrogen is displaced. If the metal is active enough for this to happen, a metal hydroxide and hydrogen gas form. 

Another property shared by aqueous solutions of acids is that they react with many metals. All metals that are above hydrogen in the activity series react with acids to produce hydrogen gas. The reaction is caused by the hydronium ion present in the solution. The presence of the hydronium ion explains why all acids behave in this way. An example is the reaction of hydrochloric acid with zinc, which is shown in Figure 3 and is represented by the following net ionic equation. 

An earlier study of the reduction with hydrogen of tin dioxide (made by the flame oxidation of stannic chloride) in the presence of 0.5 wt % Cu, Rh, Pd, Ag, Os, Ir, Pt, or Au added to the dioxide by impregnation with soluble salts gave the activity series Rh > Pt > Ir > Os > Pd Cu, Ag, and Au. The order is much more like that to be expected if the dissociative chemisorption of hydrogen is the slow step the low position of palladium may be due again to a deactivation by absorbed hydrogen. Copper is unexpectedly inactive (even inhibiting) in... 

Donors and Donees in Permanent Contact.—A spillover mechanism has been put forward to account for the catalysis of the hydrogenation of high area carbon to methane by impregnated metals.The activity series found (Rh >... 

Table 4-12 lists the activity series. When any metal listed above hydrogen in this series is added to a solution of a nonoxidizing acid such as hydrochloric acid, HCl, and sulfuric acid, H2SO4, the metal dissolves to produce hydrogen, and a salt is formed. HNO3 is the common oxidizing acid. It reacts with active metals to produce oxides of nitrogen, but not... 

The activity series of the metals, Table 4-12, tells us that copper and silver do not displace hydrogen from solutions of nonoxidizing acids. Aluminum is an active metal that can displace H2 from HCl and form aluminum chloride. 

The activity series. Table 4-12, tells us that tin and mercury cannot displace hydrogen from water. Calcium is a very active metal (see Table 4-12) that displaces hydrogen from cold water and forms calcium hydroxide, a strong base. 

One element displaces another from a compound Element + compound — element 4 compound Activity series (Table 4-12) summarizes metals and hydrogen halogen activities (Group VIIA) decrease going down the group... 

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