Acids and Base: Fundamentals and Properties

Acids and bases are fundamental chemical substances with distinct properties. Acids release hydrogen ions, while bases release hydroxide ions. Understanding chemical properties of Acids and base is crucial for diverse applications in science and industry.

Reaction of Acids and Bases with Metals

• When metal reacts with the acids it forms a compound called a salt and hydrogen gas.

               Acid + Metal → Salt + Hydrogen gas

              2NaOH (aq) + Zn (s)    →    Na₂ZnO₂(s)      +      H₂(g)

                                                                     (Sodium zincate)

• Reactions of metal with the bases are not possible. 

Acids and Base: Metal Carbonates and Hydrogen Carbonates Reactions

• All metal carbonates and hydrogen carbonates react with acids to give a corresponding salt, carbon dioxide and water. This interaction underscores the chemical interplay between acids and bases in producing specific compounds.
• Metal carbonate/Metal hydrogen carbonate + Acid → Salt + Carbon dioxide + Water

• Example:

1. Na₂CO₃(s) + 2HCl(aq) → 2NaCl(aq) + H₂O (l) + CO₂(g)
2. NaHCO₃(s) + HCl(aq) → NaCl(aq) + H₂O (l) + CO₂(g)

• On passing the carbon dioxide gas evolved through lime water,

               Ca(OH)₂(aq)        +        CO₂(g)         →        CaCO₂(s)        +        H₂O(l)

                                  (Lime water)                                       (White precipitate) 

• On passing excess carbon dioxide

              CaCO₃(s) + H₂O(l) + CO₂(g) → Ca(HCO₃)2 (aq)        

• Limestone, chalk and marble are different forms of calcium carbonate.

Acids and Base: Metallic Oxides and Acid Reactions

• The general reaction between a metal oxide and an acid can be written as;

                Metal oxide + Acid → Salt + Water

                CuO(s) + 2HCl(l) → CuCl₂(l) + H₂O(l)

• Since metallic oxides react with acids to give salts and water, similar to the reaction of a base with an acid, metallic oxides are said to be basic oxides. This draws a parallel between the reactions of acids and bases, highlighting the basic nature of metallic oxides.

Acids and Base: Reaction of a Non-metallic Oxide with Base

• The general reaction between a non-metallic oxide and a base can be written as

               Nonmetallic oxide + base → Salt + Water

• Example: Calcium hydroxide, which is a base, reacts with carbon dioxide to produce salt and water. This chemical interaction exemplifies the dynamic nature of acids and bases in producing various compounds.

               Ca(OH)₂(aq) + CO₂(g) → CaCO₃(s) + H₂O(l)

• Since this is similar to the reaction between a base and an acid, it can be concluded that non-metallic oxides are acidic in nature.

Acids and Base: Common Characteristics

Acids and Bases in a Water Solution

• The separation of H+ ion from HCl molecules cannot occur in the absence of water.

               HCl + H₂O → H₃O+ + Cl– 

• Hydrogen ions cannot exist alone, but they exist after combining with water molecules. 
• Thus hydrogen ions must always be shown as H+(aq) or hydronium ion (H₃O+).

              H+ + H₃O → H₃O+ 

• Bases dissolved in water generate hydroxide (OH–) ions. For example,

NaOH (s) → Na+ (aq) + OH – (aq)

               KOH(s) → K+ (aq) + OH – (aq)

               Mg(OH)₂(s) → Mg₂ + (aq) + 2OH – (aq)  

• The process of dissolving an acid or a base in water is a highly exothermic one.
• Mixing an acid or base with water results in a decrease in the concentration of ions (H₃O+/OH–) per unit volume.
• Such a process is called dilution and the acid or the base is said to be diluted.

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