Some people have an allergic reaction to the food preservative sulfite (SO_3^2-)

Question

Some people have an allergic reaction to the food preservative sulfite (SO_3^2-). Sulfite in wine was measured by the following procedure: To 5C.0 mL of wine were added 5.00 mL of solution containing (0.8043 g KIO_3 + 5 g KI)/100 mL. Acidification with 1.0 mL of 6.0 M H_2SO_4 quantitatively converted IO_3^- Into I_3^-. The I_3^- reacted with SO_4^2- to generate SO_4^2-, leaving excess I_3^- in solution. The excess I_3^_ required 12.86 mL of 0.04318 M Na_2S_2O_3 to reach a starch end point. Write the reaction that occurs between KIO_3 and KI when the H_2SO_4 is added. (Use the lowest possible coefficients. Omit spectator ions and states-of-matter.) Write a balanced reaction between I_3^- and sulfite. (Use the lowest possible coefficients. Omit spectator ions and states-of-matter.) Find the concentration of sulfite in the wine. Express your answer in mol/L and in mg O_3^2- per liter. mol/L mg/L

Explanation / Answer

From the data

(a) Equation

KIO3 + 8KI + 3H2SO4 --> 3K2SO4 + 3KI3 + 3H2O

(b) Equation,

I3- + SO3^2- + H2O ---> 3I- + HSO4- + H+

(c) excess I3- = 0.04818 M x 12.86 ml/2 = 0.31 mmol

moles of KIO3 = 0.8043 g/214 g/mol = 3.76 mmol

moles of I3- initial = 3 x 3.76 = 11.28 mmol

moles of I3- reacted = 11.28 - 0.31 = 10.97 mmol

moles of SO3^2- present = 10.97 mmol

concentration of sulfite in wine = 10.97 x 80.06/0.06886 = 12754.26 mg/L

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