Label five, 13 x 100 mm test tubes with S, 1, 2, 3, and 4. Use a pipet to add 4
mL of the 25 mL sample solution to each of the five test tubes. Use the 1 mL
graduated pipet to transfer 0.20 mL of the 100 mg/liter iron solution to 1, 0.30
mL to tube 2, 0.40 mL to tube 3, and 0.60 mL to tube 4.