HI,

I think this is just a matter of keeping things straight.

So, in g/mol, K2Cr2O7 MW is 294.185 and MW of Cr is 51.9961. The wt fraction of 2 Cr in K2Cr2O7 is 0.35 or 35%. Next, 125mg Cr(VI) per 1L solution should then be 31.25mg Cr(VI) in 250 mL solution. Now, with 31.25 mg Cr(VI) in 250 mL, two Cr is 35% the weight of K2Cr2O7 and with a mas balance of: 35% of (X mass of K2Cr2O7) = (31.25 mg Cr), So X = 89.2857 mg K2Cr2O7. So I would add 89.2857 mg of K2Cr2O7 molecule and put that in 250 mL water, and that should be at concentration of 125 mg Cr per L solution. Assuming ideal solution and that the volume does not change from mixing that should be 125mg/L. I haven't done that in years but should be correct. If not I blame it on my hunger and waiting for dinner. Good luck.

Dear Dr. John Reye, the steps you provided are logical and should be useful to Nardi Rosier

Regards,

Egbuna

you have to calculate the exact weight of Cr atom then you can solve your problem

you need 353.61mg of K2Cr2O7 to prepare 125mg/L or Cr ion

Kindly check http://shodhganga.inflibnet.ac.in/bitstream/10603/12755/11/11_chapter%203.pdf

Also check https://www.who.int/water_sanitation_health/water-quality/guidelines/chemicals/draft-chromium-190924.pdf

I am a bit reluctant to answer because I feel quite uneasy when considering that a person who is unable to solve this simple problem should handle such a dangerous material as dichromate...

Greetings Nardi Rosier

Calculated the K2Cr2O7 mass using the Dimensional Analysis method.

Concentration is commonly quantified by developing calibration curves for the specific analyte. This can be done by measuring the signal of well-known standards of different concentrations with either HPLC or UV-VIS. There is a wide variety of spectroscopic techniques that can be used; however, you can adapt with the ones available in the lab.

Hope this helped.

You should change your profession.