Give suitable reason for the following statements
1. Rain water conducts electricity but distilled water doesn't.
2. We feel burning sensation in the stomach when we over eat.
3. A tarnished copper vessel regains its shine when rubbed with lemon.
4. The crystal of washing soda change to white powder on exposed to air.
5. An aqueous solution of NaCl is neutral but an aqueous solution of Na2CO3 is basic.
Answers
1) Distilled water cannot conduct electricity because it does not contain ions while rain water conducts electricity as it contains ions due to presence of dissolved salts in it.
2)When we eat food, then Hydro chloric Acid is released in our stomach to help us digest that food properly. But, when we overeat, Hydro chloric Acid is produced in a greater amount, which makes our stomach acidic and leads to a burning sensation.
3) Copper vessels are tarnished due to the layer of oxide formed on the surface. The oxides are basic in nature while, lemon exhibits acidic nature. When we rub it on the surface of tarnished vessel, basic copper oxide reacts with acidic lemon to form salt, which is then washed away while cleaning the vessel with water.
4) When sodium carbonate crystals are exposed to air They lose water of crystallization and turn to white powder. This process of loosing water of crystallization when exposed to air is called efflorescence. When sodium carbonate crystals are exposed to air They lose water of crystallization and turn to white powder.
5) NaCl is salt of strong acid HCl and strong base NaOH. It does not undergo hydrolysis as there is no reaction between ions of salt NaCl with water.Aqueous solution of NaCl contains equal number of H+ and OH- ions,hence it is neutral in nature.On other hand,sodium carbonate is a salt of weak acid H₂CO₃ and strong base NaOH. When it is dissolved in water,it undergo anionic hydrolysis.Thus salt solution contains OH- ions. Hence aqueous solution of sodium carbonate is basic in nature.