Could someone please help me with this question? The blood alcohol(C2H5OH) level

Question

Could someone please help me with this question? The blood alcohol(C2H5OH) level can be determined by titratinga sample of blood plasma with an acidic potassium dichromatesolution, resulting in the production of Cr3+(aq) and carbondioxide. The reaction can be monitored because the dichromateion(Cr2O7)(-2) is orange in solution, and the Cr3+ ion is green.The unbalanced redox equation is Cr2O7(-2)aq + C2H5OH(aq) -> Cr(3+)aq + CO2(g) If 31.05mL of 0.0600M potassium dichromate solution isrequired to titrate 30.0g of blood plasma, determine the masspercent of alcohol in the blood. I don't get how potassium dichromate comes suddenly when Ican't find any potassium... Please help me!
Thank you very much! Could someone please help me with this question? The blood alcohol(C2H5OH) level can be determined by titratinga sample of blood plasma with an acidic potassium dichromatesolution, resulting in the production of Cr3+(aq) and carbondioxide. The reaction can be monitored because the dichromateion(Cr2O7)(-2) is orange in solution, and the Cr3+ ion is green.The unbalanced redox equation is Cr2O7(-2)aq + C2H5OH(aq) -> Cr(3+)aq + CO2(g) If 31.05mL of 0.0600M potassium dichromate solution isrequired to titrate 30.0g of blood plasma, determine the masspercent of alcohol in the blood. I don't get how potassium dichromate comes suddenly when Ican't find any potassium... Please help me!
Thank you very much!

Explanation / Answer

      Potassium dichromate reactswith ethyl alcohol according to the following reaction:                       16H+ + 2Cr2O72- + C2H5OH    ------> 4Cr3+ + 11 H2O + 2CO2 So we see that 1 mole of ethyl alcohol reacts with 2 moles ofdi chromate ion. Here potassium is only the spectator ion and doesnot participate in redox reaction. So it is not written in theabove equation.    Moles of dichromate = Molarity * volume                                    =0.06 M * 0.03105 L                                    =0.001863 moles So moles of alcohol = 0.001863 / 2 = 0.0009315 moles Mass of alcohol = Molar mass * number of moles                         = 46.06 g/mol * 0.0009315 moles                          =0.0429 g Mass of blood plasma = 30 g So Mass percent of alcohol in the blood = ( Mass of alcohol /Total mass ) * 100                                                             = ( 0.0429g / 30g) * 100                                                              =0.143 % So we see that 1 mole of ethyl alcohol reacts with 2 moles ofdi chromate ion. Here potassium is only the spectator ion and doesnot participate in redox reaction. So it is not written in theabove equation.    Moles of dichromate = Molarity * volume                                    =0.06 M * 0.03105 L                                    =0.001863 moles So moles of alcohol = 0.001863 / 2 = 0.0009315 moles Mass of alcohol = Molar mass * number of moles                         = 46.06 g/mol * 0.0009315 moles                          =0.0429 g Mass of blood plasma = 30 g So Mass percent of alcohol in the blood = ( Mass of alcohol /Total mass ) * 100                                                             = ( 0.0429g / 30g) * 100                                                              =0.143 %

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