A student uses the following method to determine the percentage by mass of the painkiller aspirin, C9H8O4(s), in some tablets. step 1 Grind five tablets into a powder. step 2 Use a weighing boat to accurately weigh by difference approximately 0.4 g of powdered tablets into a pear-shaped flask containing anti-bumping granules. step 3 Add 25 cm³ of aqueous 1 moldm¯³ sodium hydroxide, NaOH(aq), to the pear-shaped flask, forming mixture A. step 4 Reflux mixture A for 20 minutes. step 5 Allow mixture A to cool and then filter into a small beaker. Label the filtrate solution B. step 6 Add 30cm³ of alkaline aqueous iodine to solution B and leave to stand for 1 hour. A precipitate, C, (C6H2I2O)2(s), will form. step 7 Filter the resulting mixture under reduced pressure. Wash the residue, C, with a small volume of cold distilled water. step 8 Allow solid C to dry. step 9 Weigh solid C and record its mass. Alkaline aqueous iodine is irritating to the skin and eyes.