Question

An aqueous ethylene glycol (HOCH2CH2OH, FW = 62.07 g/mol) solution with a mass of 296.7 mg is titrated with 65.9 mL of 0.0705 M Ce4 in 4 M HClO4. The solution is held at 60°C for 15 minutes to oxidize the ethylene glycol to formic acid (HCO2H) and carbon dioxide. The excess Ce4 is titrated with 12.07 mL of 0.0375 M Fe2 to a ferroin end point. What is the mass percent of ethylene glycol in the unknown solution?

Answer 1

First we need to write the reaction between Ethylene glycol (EG) and Ce⁴⁺ which is a redox reaction where EG is oxidized to formic acid HCOOH and Ce⁴⁺ is reduced to Ce³⁺. Next, we will need to balance the equation using the acid method where we will add H₂O molecules to balance O atoms and then we will add H⁺ to balance H atoms, and finally we will add electrons to balance the carges. See the detailed procedure below for the balance of the equation.

Now we will need to calculate how much the excess of Ce⁴⁺ was. Since the reaction between Ce⁴⁺ and Fe²⁺ occurs in a 1:1 mole basis we can use the C1V1 = C2V2 formula. See the detailed procedure below for this part of the problem.

Then we calculate how much Ce⁴⁺ was used in the titration of EG just by substracting the excess from the total volume used. Next, we used the volume of Ce⁴⁺ used in the titration and the balanced redox reaction to calculate how many grams of EG the sample contained and finally we just divide those grams over the total mass of the sample (0.2967g) and then multiply times 100. See the detailed procedure below.

The answer is 14.62%

Detailed procedure: