Acids, Bases and Salt — Important Questions

Dark pink (magenta)

Step 1: China rose petals are used to prepare a natural indicator by soaking them in warm water. Step 2: The coloured water obtained acts as an indicator. Step 3: When this indicator is added to an acidic solution, it turns dark pink or magenta in colour. Step 4: When added to a basic solution, it turns green. Step 5: Neutral solutions do not produce a significant colour change. So magenta = acid, green = base for China rose indicator.

The solution is neutral

Step 1: Litmus is a reliable indicator that changes colour based on the nature of the solution. Step 2: Acids turn blue litmus red. Bases turn red litmus blue. Step 3: If NEITHER red nor blue litmus changes colour, the solution is neither acidic nor basic. Step 4: Such a solution is called a neutral solution. Step 5: Common examples of neutral substances include pure water (distilled water) and sugar solution — they have no effect on litmus paper.

Formic acid

Step 1: When an ant bites, it releases a liquid into the skin. Step 2: This liquid is acidic in nature and causes a burning or stinging sensation. Step 3: The acid found in an ant's sting is called formic acid. Step 4: This acid irritates the skin and causes pain. Step 5: To neutralise formic acid, we apply a base like moist baking soda (sodium hydrogencarbonate) or calamine solution (which contains zinc carbonate) — this neutralisation reaction reduces the pain.

Salt and water

Step 1: When an acid and a base are mixed, they react with each other. Step 2: This reaction is called neutralisation because the acid neutralises the base and vice versa. Step 3: The products of this reaction are always salt and water, along with the release of heat. Step 4: The general equation is: Acid + Base → Salt + Water (+ Heat). Step 5: Example: Hydrochloric acid (HCl) + Sodium hydroxide (NaOH) → Sodium chloride (NaCl) + Water (H₂O). Sodium chloride is common table salt!