To obtain chlorine from bleaching powder (calcium hypochlorite, Ca(OCl)₂), you need to add a dilute acid, such as hydrochloric acid (HCl).

Here's the chemical reaction:

Ca(OCl)₂ + 2HCl → CaCl₂ + H₂O + Cl₂

Explanation:

* Bleaching powder contains calcium hypochlorite, which is a source of hypochlorite ions (OCl⁻).

* When acid is added, it reacts with hypochlorite ions to form chlorine gas (Cl₂), water (H₂O), and calcium chloride (CaCl₂).

Important Note:

* The reaction is exothermic, meaning it releases heat.

* Chlorine gas is toxic and should be handled with caution.

* Always perform this experiment in a well-ventilated area and wear appropriate safety gear.