As explained in the text “Metal reactivity order”, for any reaction to occur, it is necessary to satisfy certain conditions, such as contacting the reagents and having chemical affinity between them, which means that they must interact in order to enable the formation of new substances.
When we put metals to react with acids, the vast majority have this chemical affinity and react. However, the same does not happen when put to react with bases and with water.
Remembering that, according to Arrhenius' definition, a base is any substance that in aqueous solution releases the hydroxyl OH as the only anion-.
The only metals that react with bases are aluminum (Al), zinc (Zn), lead (Pb) and tin (Sn).
Note below the reaction between sodium hydroxide base (NaOH) with aluminum and zinc, respectively:
2 Al(s) + 2 NaOH(here) + H2O → 2 NaAlO2(aq) + 3 H2(g)
base metal salt hydrogen gas
sodium aluminate
Zn(s) + 2 NaOH(here) → 2 In2ZnO2(aq) + H2(g)
base metal salt hydrogen gas
sodium zincate
Note that in both cases the products formed were a salt and hydrogen gas. Therefore,
when the mentioned metals react with a strong base, the products will always be unusual salts and hydrogen gas.The metals that react with water are the alkali metals (elements of family 1 or IA - Li, Na, K, Rb, Cs and Fr), the alkaline earth metals (elements of family 2 or II A - Ca, Sr, Ba and Ra), magnesium (Mg), iron (Fe) and zinc (Zn).
Alkali metals, in particular, are extremely reactive, both with water and even with oxygen in the air. Therefore, they are usually stored submerged in kerosene.
This is because they have a great tendency to lose electrons, oxidize and act as strong reducing agents.
In contact with water, all alkali and alkaline earth metals form a base and hydrogen gas as products.
For example, the reaction between sodium and water produces sodium hydroxide and hydrogen gas, as shown in the equation below:
2 In(s) + 2 H2O(1)→2 NaOH(here) + H2(g)
When we put sodium in contact with water, a violent reaction will occur which, if we put the acid-base phenolphthalein indicator, we will see the appearance of a pink color, evidencing the presence from the base. Furthermore, the greater the amount of sodium placed, the greater the reaction visualized will be, because the hydrogen released combusts when it comes into contact with the oxygen present in the air.
Violent reaction between sodium and water breaks glass container*
This reactivity increases as the periods of the alkali metals increase, that is, it grows in this direction:
Li < Na < K < Rb < Cs
Lithium reacts more slowly with water than other alkali metals. The reaction of potassium (K) with water is already strong enough to ignite hydrogen (on fire), even with small amounts of reactants. With rubidium and cesium, this small-scale reaction is already dangerously explosive, and because these metals are denser than water, the reaction takes place below its surface.
Now look at an example of a reaction between calcium, an alkaline earth metal, and water:
Here(s) + 2 H2O(1)→ Ca(OH)2(aq) + H2(g)
In the case of other metals (magnesium, iron and zinc), the reaction only occurs under heating and the products formed in the reaction with water are oxides and hydrogen gas:
mg(s) + H2O(v)→ MgO(s) + H2(g)
3 Fe(s) + 4 H2O(v)→ Fe3O4(s) + 4 H2(g)
Zn(s) + H2O(v)→ ZnO(s) + H2(g)
*Image author: Tavoromann
By Jennifer Fogaça
Graduated in Chemistry
Source: Brazil School - https://brasilescola.uol.com.br/quimica/reatividade-dos-metais-com-agua-bases.htm