To Understand the concept, Let us do this small experiment
Observation- You will observe that the magnesium ribbon burns with a dazzling white flame and forms a white residue which falls on the glass plate
Actually the magnesium ribbon chemically reacts with oxygen present in the air to form magnesium oxide.
Divide the residue into two parts .
Take the second part of magnesium oxide in a clean test tube
Metals reacts with oxygen to form respective oxides
Oxides dissolve with water to form respective hydro oxides which are basic in nature
Metal + Water ⇨ Metal hydroxide + Hydrogen
Reaction of sodium metal with water: Sodium metal forms sodium hydroxide and liberates hydrogen gas along with lot of heat when reacts with water.
Na + H2O ⇨ NaOH + H2
Reaction of potassium metal with water: Potassium metal forms potassium hydroxide and liberates hydrogen gas along with lot of heat when reacts with water.
K + H2O ⇨ KOH + H2
Reaction of calcium metal with water: Calcium forms calcium hydroxide along with hydrogen gas and heat when reacts with water.
Ca + 2H2O ⇨ Ca(OH)2 + H2
Reaction of magnesium metal with water: Magnesium metal reacts with water slowly and forms magnesium hydroxide and hydrogen gas.
Mg + 2H2O ⇨ Mg(OH)2 + H2
When steam is passed over magnesium metal, magnesium oxide and hydrogen gas are formed.
Mg + H2O ⇨ MgO + H2
Reaction of aluminium metal with water: Reaction of aluminium metal with cold water is too slow to come into notice. But when steam is passed over aluminium metal; aluminium oxide and hydrogen gas are produced.
2Al + 3H2O ⇨ Al2O3 + 2H2
Reaction of zinc metal with water: Zinc metal produces zinc oxide and hydrogen gas when steam is passed over it. Zinc does not react with cold water.
Zn + H2O ⇨ ZnO + H2
Reaction of Iron with water: Reaction of iron with cold water is very slow and come into notice after a long time. Iron forms rust (iron oxide) when reacts with moisture present in atmosphere.
Iron oxide and hydrogen gas are formed by passing of steam over iron metal.
3Fe + 4H2O ⇨ Fe3O4 + 4H2
Other metals usually do not react with water or react very slowly.
When a metal reacts with dilute acid, salts are formed. During this reaction hydrogen gas is evolved. In other words, when a metal is added to dilute acids, salt and hydrogen gas are formed.
Alkali + Metal ⇨ Salt + Hydrogen
Example: Sodium hydroxide gives hydrogen gas and sodium zincate when reacts with zinc metal.
2NaOH + Zn ⇨ Na2ZnO2 + H2
2NaOH + 2Al + 2H2O ⇨ 2NaAlO2 + 2H2
To study a single displacement reaction with the help of iron nails and copper sulfate solution.
What is a displacement reaction?
Displacement reaction is a chemical reaction in which a more reactive element displaces a less reactive element from its compound.
Both metals and non-metals take part in displacement reactions.
Example : Reaction of iron nails with copper sulphate solution.
Examples are halogens. The activity series of halogen is F > Cl > Br > I.
An important thing to remember with single displacement reaction is that elements that form cations can only displace cations and elements that form anions can only displace anions.
Classification of single displacement reaction:
In this reaction, one cation replaces another one from its solution. A cation is a positively charged ion or metal. All metal displacement reactions are cation replacement reactions.
Let us demonstrate some examples of cation replacement reactions.
For example :The metals such as potassium, sodium, lithium, etc. react more vigorously with dilute acids forming metal salts and hydrogen gases.
The reaction Zn with dil. H2SO4 is often used in the laboratory for the preparation of hydrogen gas.
If a less reactive metal is added to a salt solution of more reactive metal, nothing will happen.
In this reaction, one anion replaces another one from its solution. An anion is a negatively charged ion or non-metal. For example, more reactive halogen replaces less reactive halogen from its solution.