Acids, Bases and Salts — Important Questions

Salt, water and carbon dioxide are formed

Step 1: When acids react with metal carbonates, a characteristic pattern is followed. Step 2: The general reaction is: Metal carbonate + Acid → Salt + Water + Carbon dioxide. Step 3: For example: CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂. Step 4: The carbon dioxide gas can be identified by passing it through lime water, which turns milky. Step 5: This reaction is different from acid-metal reactions which produce hydrogen gas instead of CO₂.

Phenolphthalein

Step 1: Different indicators show specific colors in acidic and basic solutions. Step 2: Phenolphthalein is colorless in acidic and neutral solutions but turns pink in basic solutions. Step 3: Litmus turns blue (not pink) in basic solutions and red in acidic solutions. Step 4: Methyl orange turns yellow in basic solutions and red in acidic solutions. Step 5: Universal indicator shows various colors depending on pH, not specifically pink for all basic solutions.

CaSO₄.½H₂O

Step 1: Plaster of Paris is calcium sulfate hemihydrate, meaning it has half a water molecule per formula unit. Step 2: Its formula is CaSO₄.½H₂O or 2CaSO₄.H₂O (both represent the same compound). Step 3: It is made by heating gypsum (CaSO₄.2H₂O) at about 100°C to remove 1.5 water molecules. Step 4: CaCO₃ is calcium carbonate (limestone) and Ca(OH)₂ is calcium hydroxide (slaked lime). Step 5: When mixed with water, it reforms gypsum and hardens, making it useful for casts and construction.

Neutralization

Step 1: When an acid reacts with a base, they neutralize each other's properties. Step 2: This reaction is called neutralization because the acidic and basic properties are neutralized. Step 3: The general reaction is: Acid + Base → Salt + Water. Step 4: For example: HCl + NaOH → NaCl + H₂O. Step 5: The resulting solution becomes neutral (pH = 7) when equivalent amounts of acid and base react completely.