ACIDS, BASES, & SALTS

1. Acid: - An acid is defined as a substance whose water solution tastes sour, turns blue litmus red, and neutralizes bases. example- lactic, citric, Hydrochloric acid (HCl), Sulphuric acid (H2SO4), etc.
2. Base: - A substance is called base if its aqueous solution tastes bitter, turns red litmus blue, or neutralizes acids. example- Baking soda, bleach, NaOH, KOH, etc.
3. Salt: - Salt is a neutral substance whose aqueous solution does not affect litmus. example- Sodium chloride (NaCl), Potassium chloride (KCl), etc.

      

 What is litmus paper?

 Litmus is mainly used to assess whether a solution is acidic or basic. The color transition occurs over the pH range 4.5–8.3 at 25 °C, with light blue litmus paper turning red under acidic conditions and red litmus paper turning blue under basic or alkaline conditions. Purple litmus paper is neutral.

 

                                            1. CHEMICAL PROPERTIES OF ACID AND BASES

Chemical Properties of Acid and Bases

1. Reactions of Acids and Bases with Metals

When a metal reacts with an acid, it generally displaces hydrogen from the acids. This leads to the evolution of hydrogen gas. For example

 

2. The Reaction of Metal Carbonates/Metal Bicarbonates with Acids

Metal carbonates/metal bicarbonates react with acids to produce salt, carbon dioxide, and water. For example

3. The Reaction of Metal Oxide with Acids

Metal oxides react with acids to produce salt and water. For example

4. The Reaction of Non-metal Oxide with Bases

Non-metal oxides react with bases to produce salt and water. For example 

5. The Reaction between Acids and Bases

Acids react with bases to produce salt and water. The reaction between acids and bases to give salts is known as the neutralization reaction. For example

 2. HOW STRONG ARE ACID OR BASE SOLUTIONS?

The amount of H⁺ present in a solution can be measured by using a universal indicator. It is a mixture of several indicators. It shows different colors at different concentrations of hydrogen ions. A pH scale is a scale for measuring hydrogen ion concentration in a solution.

1. pH is measured from 0 (very acidic) to 14 (very alkaline).
2. The strength of acids and bases depends on the number of H+ ions and OH– ions produced, respectively.

3. The higher the H⁺ ion concentration lower the pH value.

4. The pH of a neutral solution is 7.
5. The pH of an acidic solution is less than 7.

6. The pH of the basic solution is more than 7.

7. The strength of acids and bases depends on the number of H+ ions and OH– ions produced, respectively.

pH of some common substances shown on a paper

                                             3. IMPORTANCE OF pH IN EVERYDAY LIFE

 1. Our body works within the pH range of 7.0 to 7.8.

2. When pH of rainwater is less than 5.6, it is called acid rain. When it flows into the river it lowers the       pH value of river water. it adversely affects the survival of aquatic life.

3. pH change as the cause of tooth decay. Tooth decay starts when the pH of the mouth is lower than          5.5. Using toothpaste, which is generally basic, for cleaning the teeth can neutralize the excess acid        and prevent tooth decay.

4. Self-defence by animals and plants through chemical warfare

    Bee-sting leaves an acid that causes pain and irritation. Using a mild base like baking soda on the            stung area relieves.

5. Acids on other planets. The atmosphere of Venus is made up of thick white and yellowish clouds of          sulphuric acid.

                              

                                                   4. MORE ABOUT SALTS

                                                           5. CHEMICALS FROM COMMON SALT

Sodium hydroxide: - When electricity is passed through an aqueous solution of sodium chloride (called brine), it decomposes to form sodium hydroxide. The process is called the chlor-alkali process because of the products formed– chlor for chlorine and alkali for sodium hydroxide.

                               2NaCl(aq) + 2H₂O(l) → 2NaOH(aq) + Cl₂ (g) + H₂ (g)

 

Bleaching powder: - Bleaching powder is produced by the action of chlorine on dry slaked lime [Ca(OH)₂ ].

                                                   Ca (OH)₂ + Cl₂ → CaOCl₂ + H₂O

Baking soda: - The chemical name of the compound is sodium hydrogencarbonate (NaHCO₃ ). It is produced using sodium chloride as one of the raw materials.

                                                  NaCl + H₂O + CO + NH₃ → NH₄ Cl + NaHCO₃

 

Washing soda: - Another chemical that can be obtained from sodium chloride is Na₂CO₃ .10H₂O (washing soda). It is also a basic salt.

                                                    Na₂CO₃ + 10 H₂O → Na₂CO₃.10 H₂O