Some people have an allergic reaction to the food preservative sulfite (SO32-). Sulfite in wine was measured by the following procedure: To 50.0 mL of wine were added 5.00 mL of solution containing (0.804 3 g KIO3 + 5 g KI)/100 mL. Acidification with 1.0 mL of 6.0 M H2SO4 quantitatively converted IO-3 into I-3 . The I-3 reacted with SO32- to generate SO24 , leaving excess I-3 in solution. The excess I-3 required 12.86 mL of 0.048 18 M Na2S2O3 to reach a starch end point.
(a) Write the reaction that occurs when H2SO4 is added to KIO3 + KI and explain why 5 g KI were added to the stock solution. Is it necessary to measure out 5 g very accurately? Is it necessary to measure 1.0 mL of H2SO4 very accurately?
(b) Write a balanced reaction between I-3 and sulfite.
(c) Find the concentration of sulfite in the wine. Express your answer in mol/L and in mg SO32- per liter.
(d) t test. Another wine was found to contain 277.7 mg SO32-/L with a standard deviation of 2.2 mg/L for three determinations by the iodimetric method. A spectrophotometric method gave 273.2 2.1 mg/L in three determinations. Are these results significantly different at the 95% confidence level?