# Problem: The US Environmental Protection Agency (EPA) places limits on the quantities of toxic substances that may be discharged into the sewer system. Limits have been established for a variety of substances, including hexavalent chromium, which is limited to 0.50 mg/L. If an industry is discharging hexavalent chromium as potassium dichromate (K2Cr2O7), what is the maximum permissible molarity of that substance?

###### FREE Expert Solution

Transition metals can have numerous valency or oxidation numbers.

The most common oxidation states of chromium are Cr2+, Cr3+ and the hexavalent Cr6+.

Chromium in potassium dichromate is hexavalent.

K2Cr2O7

Oxidation states: K+ → (+1) x 2 = +2

O2- → (-2) x 7 = -14

Crx → (X) x 2 = 2X

Overall oxidation state: (+2) + 2X + (-14) = 0

2X = 14-2

X = +6

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###### Problem Details

The US Environmental Protection Agency (EPA) places limits on the quantities of toxic substances that may be discharged into the sewer system. Limits have been established for a variety of substances, including hexavalent chromium, which is limited to 0.50 mg/L. If an industry is discharging hexavalent chromium as potassium dichromate (K2Cr2O7), what is the maximum permissible molarity of that substance?