1. To prepare a comparison solution, 0.258 g of lead nitrate was dissolved in 250 ml of water. After treating 5 ml of the solution with dithizone, 50 ml of a colored solution was obtained. The colored compound was extracted with 10 ml of chloroform, and the optical density (absorption) of the chloroform layer was 0.35.
1 liter of waste water was evaporated to 100 ml. After treating 10 ml of this solution with dithizone bio, 25 ml of a colored solution was obtained. The colored compound was extracted with 10 ml and the optical density of the chloroform layer in the same cuvette was 0.14. Determine the concentration of lead ions in water (mg/l).

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