Final answer:
Insufficient information is provided to calculate the exact mass of bleaching powder needed to produce 500 cm³ of chlorine gas, as the chemical composition of the bleaching powder and its molar mass are not given.
Step-by-step explanation:
To calculate the mass of bleaching powder needed to produce 500 cm³ of chlorine gas at 25°C and a pressure of 1.2*10⁵ N/m², we need to use the Ideal Gas Law, which is PV = nRT. However, the information given in the question is insufficient to provide a definitive answer, as the molar mass of the bleaching powder and its specific chemical composition (which affects the amount of chlorine produced per mole) are not provided. Under standard conditions, chlorine gas has a molar mass of approximately 70.906 g/mol, which is based on its isotopic distribution predominantly of chlorine-35 and chlorine-37. Using the Ideal Gas Law formula, where P is pressure, V is volume, n is the number of moles, R is the gas constant, and T is temperature, we could solve for n, and then use the compound's molar mass to calculate the mass needed. However, without knowing the chemical reaction or the molar mass of bleaching powder, we cannot provide a specific mass. For an accurate calculation, additional information on the chemical formula of bleaching powder and the stoichiometry of the reaction is required.