A 100 mL volumetric flask is often calibrated by weighing the volume of water ne

Question

A 100 mL volumetric flask is often calibrated by weighing the volume of water needed to fill it to the mark. Of these possible sources of error, which is most likely to cause serious error in the result? An unknown chloride sample was analyzed by the Volhard method. A 0.4100 g sample was dissolved in water, then a 50 mL pipet of 0.1420 M AgNO3 was added to the sample solution. The excess Ag+ was then back titrated with 12.40 mL of 0.1200 M KSCN solution. Assuming that proper techniques and precautions were observed thoughout the experiment, calculate the % Cl in the sample.

Explanation / Answer

volume of unreacted 0.1420 M AgNO3 reacts with 12.40 mL of 0.1200M KSCN msolution.

volume of unreacted 0.1420 M AgNO3= (12.40 mL x 0.12 M)/ 0.1420 M= 10.48 mL of unreacted 0.1420 M AgNO3

The reacted 0.1420 M AgNO3 is (50 mL -10.48 mL)= 39.52 mL (V) of 0.1420 M AgNO3 (M) reacts with 0.410 g of sample.

Percentage of Cl-= (V x M x Mol.wt of Cl- x100)/ wt. of sample x 1000

Percentage of Cl-= (39.52 x 0.1420 x 35.453 x100)/ 0.410 x 1000

Percentage of Cl-= 48.52 %

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