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Chapter 17: Q19P (page 428)

17-19. In the Figure, 17-11, 2.00nmol fructose was introduced at the time of the arrow. How many electrons are lost in the oxidation of one molecule of fructose? Compare the theoretical number of coulombs with the observed number of coulombs for complete oxidation of the sample.

Short Answer

Expert verified

The n electron isn(e-)=4.10-9mol and the charge isq=3.86.10-4C

Step by step solution

01

Fructose oxidation:

The body oxidizes a considerable proportion of dietary fructose to create energy. At rest, fructose may be preferentially or comparably consumed to create energy like glucose, however, during exercise, glucose seems to be more preferentially utilized to produce energy by the body.

02

Find oxidation of one fructose molecule:

The reaction is:

D-fructose→5-keto-D-fructose+2H++2e-

The electron is:

n(e-)n(fructose)=21n(e-)=2.n(fructose)n(e-)=2.2.10-9moln(e-)=4.10-9mol

The charge is:

q=n(e-).Z.Fq=4.10-9mol.1.96485C/molq=3.86.10-4C

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Most popular questions from this chapter

Fundamentals of Electrolysis

17-9. A lead-acid battery in a car has six cells in series, each delivering close to2.0Vfor a total of 12V when the battery is discharging. Recharging requires ~2.4V per cell, or ~14V for the entire battery. 55Explain these observations in terms of Equation 17-6.

Ti3+ is to be generated in 0.10MHClO4 for coulometric reduction of azobenzene.

TiO2++2H++e−⇌Ti3++H2OE0=0.100V4Ti3++C6H5N=NC6H5+4H2O→2C6H5NH2+4TiO2++4H+

At the counter electrode, water is oxidized, and \(\mathrm{O}_{2}\) is liberated at a pressure of \(0.20\) bar. Both electrodes are made of smooth Pt, and each has a total surface area of 1.00cm2. The rate of reduction of the azobenzene is 25.9nmol/s , and the resistance of the solution between the generator electrodes is 52.4Ω.

  1. Calculate the current density (A/m2)at the electrode surface. Use Table 17-1 to estimate the overpotential for O2liberation.
  2. Calculate the cathode potential (versus S.H.E.) assuming that role="math" localid="1668356673323" [TiO2+surface]=[TiO2+]bulk=0.050Mand [Ti3+]surface=0.10M.
  3. Calculate the anode potential (versus S.H.E.).
  4. What should the applied voltage be?

The chlor-alkali process 54in which seawater is electrolyzed to make CI2 andNaOH, is the second most important commercial electrolysis, behindAIproduction.

Anode: CI-→12CI2+e-

HgCathode:Na++H2O+e-→NaOH+12H2

The Nafion membrane (page 421) used to separate the anode and cathode compartments resists chemical attack. Its anionic side chains permit conduction ofNa+ , but not anions. The cathode compartment contains pure water, and the anode compartment contains seawater from which Ca2+ and Mg2+ have been removed. Explain how the membrane allows NaOH to be formed free ofNaCI.

What is the purpose of the Nafion the membrane in Figure 17-33

Coulometric titration of sulfite in wine. Sulfur dioxide is added to many foods as a preservative. In aqueous solution, the following species are in equilibrium:

Bisulfite reacts with aldehydes in food near neutral pH:


Sulfite is released from the adduct in 2MNaOH and can be analyzed by its reaction with I3- to give I-and sulfate. ExcessI3- 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 and the adduct in Reaction . 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 0.8gNaOH and dilute to 10.00mL. The releases sulfite from its organic adducts.

2. Generate I3-at the working electrode (the anode) by passing a known current for a known time through the cell in Figure 17 - 10. The cell containsofacetate buffer () plus. In the cathode compartment, is reduced to H2+OH-. The frit retards diffusion of into the main compartment, where it would react with I3- to giveIO-.

3. Generate I3- at the anode with a current of for.

4. Inject 2.000mL of the wine/ solution into the cell, where the sulfite reacts with leaving excess.

5. Add of thiosulfate to consume by Reaction and leave excess thiosulfate.

6. Add starch indicator to the cell and generate freshI3- with a constant current of 10.0mA. A time of 131s 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 isand the dominant form of sulfuric acid is HSO42-. Write balanced reactions between andand between I3-and HSO3-thiosulfate.

(d) Find the concentration of total sulfite in undiluted wine.
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