Question

The following data was obtained during a precipitation titration for chloride. In this experiment, a 5.00 mL sample of sea water was diluted to 250.00 mL prior to titrations, For the titration. KSCN and AgNO_3 were each standardized individually before being used to analyze the sea water sample. KSCN was standardized against a NIST-certified reference standard with a concentration of 0.01000 M Ag'. The AgNO_3 solution was standardized against dried sodium chloride measured in lab. Using these solutions, the AgNO_3 solution was added to 25.00 mL aliquots of the sea water solution until no visible precipitate formed with the addition of more AgNO_3. At this point, an additional 3.00 ml. of AgNO_3 was added to ensure excess. The total volume of AgNO_3 added is given in the data below (including the 3.00 mL excess). The precipitate was filtered and washed with 10.00 ml. of dilute nitric acid. The supernatant was then spiked with 5.00 ml. of concentrated HNO_3 and 5.00 mL 0.020 M Fe^3+. The resultant solution was titrated with the standardized KSCN to a red endpoint. Calculate the mass percent of NaCl in the original sea water sample and its absolute standard deviation.

Answer 1

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