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?

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Our data indicates that this problem or a close variation was asked in Chemistry - OpenStax 2015th Edition. You can also practice Chemistry - OpenStax 2015th Edition practice problems.