Final answer:
To determine the percentage of available chlorine in the bleaching powder, the moles of S2O32- used in the titration were found. These were equated to the moles of available chlorine, which were then converted to grams and used to calculate the percentage of available chlorine as approximately 16%.
Step-by-step explanation:
To calculate the percentage of available chlorine in the bleaching powder, the amount of liberated iodine (I2) is first determined by titration with hypo solution (Na2S2O3 or thiosulfate solution). The reaction involved is I2 + 2S2O32- → 2I- + S4O62-. To get the amount of chlorine, we calculate the moles of S2O32- used in the titration, which is equal to half the moles of I2 liberated since one mole of I2 reacts with two moles of S2O32-.
Given that 80 mL (0.08 L) of 0.2 N hypo solution was used, the number of equivalents of S2O32- is equal to the normality (N) multiplied by the volume (V) in liters, which is 0.016 equivalents. Each equivalent corresponds to one mole of Cl2, so the moles of available chlorine is also 0.016 moles.
To convert moles of available chlorine to grams, we multiply by the molar mass of Cl2 (approximately 71 g/mol), giving us approximately 1.136 g of chlorine. The percentage of available chlorine is then calculated by the formula: (mass of available Cl2 / mass of bleaching powder sample) × 100, which yields approximately 16%. So, the sample contains around 16% available chlorine by mass.