What could be the reason for storing certain medicines and chemicals in brown bottles? Think of it. 

Set up the apparatus. What changes do you observe when electricity is passed through the circuit? 
• In the colour of copper sulphate solution: 
• On the carbon rods.
• Does it happen if a carbon rod is simply kept in copper sulphate solution? Which form of energy was responsible for this chemical change? Was the energy liberated or absorbed?

• What do we do with these types of cells after their use?
• Which among these cells can be recharged and reused? 
• Do they cause environmental pollution? 

Assess the chemical reactions given below and answer the questions.

Calcium carbonate $+$ heat $\to$ Calcium oxide $+$ Carbon dioxide 

Calcium oxide $+$ water $\to$ Calcium hydroxide $+$ heat 

a) Mention the reactants and products in each case. 

b) Which among these are endothermic? Which one is exothermic?