Question

3. Using the technique for the experiment you are to conduct, a student found the concentration of potassium dichromate in waste water to be 2.69 x10- M. Calculate the ppm (parts per million; mg/L) of chromium (VI) present in the waste water.

Answer 1

Concentration of Chromium (VI) ion is 2.69 x 10-7M mol Unit M means L mg Unit ppm means L First convert mol/L to g/L Molar mass of Cr is 52 g/mol 2.69 x 10-7 mol x 52 g 139.88 x 10-79 L mol L Now convert g/L to mg/L 139.88 x 10-7g1000mg 1g mg 0.0139 L 0.0139 ppm Two chromium ions are present in K,Cr,O,. 2 =0.0139 x 2 = 0.027 ppm Answer is 0.027 ppm

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