Active metal displacing hydrogen from water

Figure 4.12 An active metal displacing hydrogen from water. Lithium dispiaces hydrogen from water in a vigorous reaction that yields an aqueous soiution of lithium hydroxide and hydrogen gas, as shown on the macroscopic scaie (fop), at the atomic scaie middle), and as a balanced equation (bottom). (For clarity, the atomic-scale view of water has been greatly simplified, and only water molecules involved in the reaction are colored red and blue.)...

Displacement reactions in which an active metal displaces hydrogen from an acid or from water (see Section 6-8, Part 2) are gas-formation reactions, but they are not metathesis reactions. 

The Group IA and IIA elements on the activity table will displace hydrogen from water, but not the other metals shown. All the metals above hydrogen will react with acidic solutions to produce hydrogen gas ... 

Very active metals can even displace hydrogen from water ... 

Very active metals can even displace hydrogen from water. The reaction of potassium, or another metal of Group lA, with water is also a displacement reaction-. 

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. 

Figure 4.13 The active metal lithium displaces hydrogen from water. Only...

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. 

FIGURE 4.15 The activity series far metals. The metals are arranged according to their ability to displace hydrogen from an acid ar water. Li (lithium) is the most reactive metal, and Au (gold) is the least reactive. 

Strategy Hydrogen displacement Any metal above hydrogen in the activity series will displace it from water or from an acid. Metals below hydrogen will not react with either water or an acid. 

An easy way to predict whether a metal or hydrogen displacement reaction will actnaUy occur is to refer to an activity series (sometimes called the electrochemical series), shown in Fignre 4.16. Basically, an activity series is a convenient summary of the results of many possible displacement reactions similar to the ones already discussed. According to this series, any metal above hydrogen will displace it from water or from an acid, but metals below hydrogen will not react with either water or an acid. In fact, any metal listed in the series will react with any metal (in a compound) below it. For example, Zn is above Cu, so zinc metal will displace copper ions from copper sulfate. 

A common chemical reaction is the displacement of hydrogen from water or acids (shown in 1 and 2 above). This reaction is a good illustration of the relative reactivity of metals and the use of the activity series. For example,... 

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. 

Hydrogen may be displaced from water by a very active metal. Alkali metals are particularly reactive with water, and the reaction of sodium with water often is exothermic enough to ignite the hydrogen gas released. 

It is only the most active metals that displace hydrogen freely from cold water nevertheless, many of the metals do react with water but for one reason or another the reaction does not progress far. We just saw that calcium hydroxide was only sparingly soluble. The hydroxides of magnesium, zinc, aluminum, lead, iron are even less soluble. Thus, although a freshly cleaned piece of metal may react with water, the hydroxide which is produced adheres to the surface as a coating which separates the metal and the water. This is the main reason why most of the fairly active metals seem to be without action on water. 

Metals more active than hydrogen displaced that element from water. Non-metals, on the other hand, if active enough, would displace the oxygen. It is obvious that this is what has happened and that the acid remaining in solution is hydrochloric acid, HC1. 

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