A chemistry student wants to determine the amount of iron present in a sample of orange juice. The student takes a 50 mL sample of orange juice and reacts it with excess potassium dichromate in acidic solution. After the reaction, the remaining potassium dichromate requires 12.75 mL of a 0.015 M ferrous ammonium sulfate solution to complete the reaction. What is the mass of iron present in the sample of orange juice?

Question

A chemistry student wants to determine the amount of iron present in a sample of orange juice. The student takes a 50 mL sample of orange juice and reacts it with excess potassium dichromate in acidic solution. After the reaction, the remaining potassium dichromate requires 12.75 mL of a 0.015 M ferrous ammonium sulfate solution to complete the reaction. What is the mass

Answer 1

First, we need to determine the moles of potassium dichromate that reacted with the ferrous ammonium sulfate. The balanced equation for the reaction between potassium dichromate and ferrous ammonium sulfate in acidic solution is:6 Fe NH4 2 SO4 2 + K2Cr2O7 + 14 H2SO4 -> 6 Fe2 SO4 3 + Cr2 SO4 3 + 2 K2SO4 + 14 NH4HSO4From the balanced equation, we can see that 6 moles of ferrous ammonium sulfate react with 1 mole of potassium dichromate.Next, we need to find the moles of ferrous ammonium sulfate used in the titration:moles of ferrous ammonium sulfate =  volume of ferrous ammonium sulfate  x  molarity of ferrous ammonium sulfate moles of ferrous ammonium sulfate =  12.75 mL  x  0.015 mol/L moles of ferrous ammonium sulfate = 0.19125 mmolNow, we can find the moles of potassium dichromate that reacted with the ferrous ammonium sulfate:moles of potassium dichromate =  moles of ferrous ammonium sulfate  / 6moles of potassium dichromate = 0.19125 mmol / 6moles of potassium dichromate = 0.031875 mmolSince the potassium dichromate was in excess, the moles of potassium dichromate that reacted with the iron in the orange juice sample is equal to the moles of potassium dichromate that reacted with the ferrous ammonium sulfate:moles of potassium dichromate reacted with iron = 0.031875 mmolThe balanced equation for the reaction between potassium dichromate and iron in acidic solution is:6 Fe2+ + K2Cr2O7 + 14 H+ -> 6 Fe3+ + 2 Cr3+ + 7 H2OFrom the balanced equation, we can see that 6 moles of iron react with 1 mole of potassium dichromate. Therefore, we can find the moles of iron in the orange juice sample:moles of iron =  moles of potassium dichromate reacted with iron  x 6moles of iron = 0.031875 mmol x 6moles of iron = 0.19125 mmolFinally, we can find the mass of iron in the orange juice sample:mass of iron =  moles of iron  x  molar mass of iron mass of iron =  0.19125 mmol  x  55.845 g/mol mass of iron = 10.68 mgSo, the mass of iron present in the 50 mL sample of orange juice is approximately 10.68 mg.