Answer in General Chemistry for Julia #156554

A 300 ml water sample was taken from a stream in Mexico City and analyzed for dissolved oxygen. Using the winkler method, 58.88 ml of 2.42 x 10^-3 M sodium thiosulfate titrant was required. Calculate the dissolved oxygen in the water and express this as mg/L.

2S₂O“_3^{-2}” + I“_3^-“ “to” 3I“^-“ + S₄O“_6^{-2}”

1000ml of 1N Na₂S₂O₃ = 8g dissolved oxygen

1N Na₂S₂O₃ = (1×2) M Na₂S₂O₃

1000ml of 2M Na₂S₂O₃ = 8g dissolved oxygen

2000 mmol Na₂S₂O₃ = 8g

1 m mol Na₂S₂O₃ = “frac{8}{2000}” g

55.88 ×2.42×10^-3 m mol Na₂S₂O₃ = “frac{8u00d755.88u00d72.42u00d710^-u00b3}{2000}”

= 0.0005409184 mg/L