Acids, Bases and Salts

Ammonia turns red litmus blue, therefore it is basic in nature.

• Source: Lichens.
• Use: It is used as an indicator to check whether a given solution is acidic or basic.

Distilled water is neutral.

Verification: Dip red litmus paper into it, it remains red. Dip blue litmus paper into it, it remains blue. Since no color change occurs in either case, it is neutral.

The reaction between an acid and a base is known as neutralization. Salt and water are produced in this process with the evolution of heat.

Reaction: Acid + Base -> Salt + Water + Heat

Example: Hydrochloric acid (HCl) + Sodium hydroxide (NaOH) -> Sodium chloride (NaCl) + Water (H2O)

(a) Nitric acid turns red litmus blue. (False)

(b) Sodium hydroxide turns blue litmus red. (False)

(c) Sodium hydroxide and hydrochloric acid neutralise each other and form salt and water. (True)

(d) Indicator is a substance which shows different colours in acidic and basic solutions. (True)

(e) Tooth decay is caused by the presence of a base. (False)

Dorji can use litmus paper or a homemade indicator (like turmeric):

1. Dip blue litmus. If it turns red, the drink is Acidic.
2. Dip red litmus. If it turns blue, the drink is Basic.
3. If there is no effect on either litmus paper, the drink is Neutral.

(a) An antacid tablet is taken when you suffer from acidity.
Antacids contain bases (like milk of magnesia) which neutralize the excessive acid produced in the stomach and provide relief.

(b) Calamine solution is applied on the skin when an ant bites.
Ant bite injects formic acid into the skin. Calamine solution contains Zinc Carbonate (a base) which neutralizes the acid.

(c) Factory waste is neutralized before disposing it into the water bodies.
Factory wastes often contain acids. If discharged directly, they can kill fish and other organisms. So, basic substances are added to neutralize them.

1. Add turmeric to all three. The one giving Red colour is **Sodium Hydroxide (Base)**.
2. Now, add a drop of this Base to the other two liquids separately to make two mixtures.
3. Check the mixtures with turmeric.
   • If the colour becomes red (and stays red), it means the liquid was neutral (Sugar solution) and now became basic due to added base.
   • If the mixture remains yellow (or warms up significantly indicating neutralization), the liquid was Acid (Hydrochloric acid) which neutralized the base.

The solution is either Basic or Neutral. Both bases and neutral substances do not change the colour of blue litmus paper. (Only acids turn blue litmus red).

When pollutants like sulphur dioxide and nitrogen dioxide dissolve in rain drops to form sulphuric acid and nitric acid, the rain becomes acidic. This is called acid rain. It damages buildings, plants and animals.

• Acids: Sour taste. Chemical nature is acidic. (e.g. Curd, lemon juice, orange juice, vinegar). derived from Latin word 'acere' meaning sour.
• Bases: Bitter taste and feel soapy. Chemical nature is basic. (e.g. Baking soda, soap, lime water).

Substances used to test whether a substance is acidic or basic.

• Litmus: Extracted from Lichens. Purple colour in distilled water. Red in Acid, Blue in Base.
• Turmeric: Yellow colour. Turns **Red** in Base. No change in Acid.
• China Rose: Turns Acid **Dark Pink (Magenta)** and Base **Green**.

• Indigestion: Stomach produces too much HCl. We take Milk of Magnesia (Magnesium hydroxide) to neutralize it.
• Ant Bite: Injects Formic acid. We rub baking soda or Calamine (Zinc Carbonate) to neutralize it.
• Soil Treatment: If soil is too acidic, treat with Quick lime (Calcium oxide). If too basic, add organic matter (releases acid).
• Factory Wastes: Acidic wastes are neutralized with basic substances before discharging into water bodies.