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Coulometric titration of sulfite in wine. 38 Sulfur dioxide is added to many foods as a

Quantitative Chemical Analysis | 8th Edition | ISBN: 9781429218153 | Authors: Daniel C. Harris ISBN: 9781429218153 475

Solution for problem 16-20 Chapter 16

Quantitative Chemical Analysis | 8th Edition

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Quantitative Chemical Analysis | 8th Edition | ISBN: 9781429218153 | Authors: Daniel C. Harris

Quantitative Chemical Analysis | 8th Edition

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Problem 16-20

Coulometric titration of sulfite in wine. 38 Sulfur dioxide is added to many foods as a preservative. In aqueous solution, the following species are in equilibrium: (A) Sulfur dioxide Sulfurous acid Bisulfite Sulfite Bisulfite reacts with aldehydes in food near neutral pH: (B) Sulfite is released from the adduct in 2 M NaOH and can be analyzed by its reaction with I 3 to give I and sulfate. Excess I 3 must be present for quantitative reaction. Here is a coulometric procedure for analysis of total sulfite in white wine. Total sulfite means all species in Reaction A and the adduct in Reaction B. We use white wine so that we can see the color of a starch-iodine end point. 1. Mix 9.00 mL of wine plus 0.8 g NaOH and dilute to 10.00 mL. The NaOH releases sulfite from its organic adducts. 2. Generate I 3 at the working electrode (the anode) by passing a known current for a known time through the cell in Figure 16-9. The cell contains 30 mL of 1 M acetate buffer (pH 3.7) plus 0.1 M KI. In the cathode compartment, H2O is reduced to H2 OH. The frit retards diffusion of OH into the main compartment, where it would react with I 3 to give IO. 3. Generate I 3 at the anode with a current of 10.0 mA for 4.00 min. 4. Inject 2.000 mL of the wine/NaOH solution into the cell, where the sulfite reacts with I 3, leaving excess I 3. 5. Add 0.500 mL of 0.050 7 M thiosulfate to consume I 3 by Reaction 15-19 and leave excess thiosulfate. 6. Add starch indicator to the cell and generate fresh I 3 with a constant current of 10.0 mA. A time of 131 s was required to consume excess thiosulfate and reach the starch end point. (a) In what pH range is each form of sulfurous acid predominant? (b) Write balanced half-reactions for the anode and cathode. (c) At pH 3.7, the dominant form of sulfurous acid is HSO 3 and the dominant form of sulfuric acid is HSO4 2. Write balanced reactions between I 3 and HSO 3 and between I 3 and thiosulfate. (d) Find the concentration of total sulfite in undiluted wine. HSO3 HO R H S

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General Chemistry Notes Week 2 Introductory Vocabulary ● Matter­ Anything that has mass and occupies space ● Mass­a quantitative measure of the amount of matter in an object ● Weight­ is a measure of the force of gravitational attraction between an object and a significantly large body (mass x acceleration due to gravity) ● Matter­ ● Elements­ a substance that cannot be separated into simpler substances by chemical means. ● Atom­ The smallest representative part of an element Atoms are the building blocks of matter Atoms combine to form molecules Molecules are a chemical combination of 2 or more atoms (ethyl butanoate pineapple)

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Chapter 16, Problem 16-20 is Solved
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Textbook: Quantitative Chemical Analysis
Edition: 8
Author: Daniel C. Harris
ISBN: 9781429218153

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Coulometric titration of sulfite in wine. 38 Sulfur dioxide is added to many foods as a