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Principles of Instrumental Analysis

7th Edition
Douglas A. Skoog + 2 others
Publisher: Cengage Learning
ISBN: 9781305577213
BuyFind

Principles of Instrumental Analysis

7th Edition
Douglas A. Skoog + 2 others
Publisher: Cengage Learning
ISBN: 9781305577213

Solutions

Chapter 25, Problem 25.15QAP
Interpretation Introduction

(a)

Interpretation:

The surface area should be determined in cm2, neglecting the area of the nanotube attachment.

Concept introduction:

Surface area of a sphere = 4πr2

r = radius of the sphere.

Interpretation Introduction

(b)

Interpretation:

The concentration gradient and the current for A at a concentration of 1.00 mM at different times should be calculated.

Concept introduction:

cAx=cA0(1πDt+1r)

cAx - concentration gradient

cA0 - concentration of A

D − diffusion coefficient

t- time after the voltage is applied

r − radius of the sphere

i=nFADcA0(1πDt+1r)

i − time dependent faradaic current

n − number of moles of electrode

F − Faraday constant

A − surface area

D − diffusion coefficient

cA0 - concentration of A

t- time after the voltage is applied

r − radius of the sphere

Interpretation Introduction

(c)

Interpretation:

The steady state current should be found

Concept introduction:

If r << d, which occurs at long times, the 1/r term predominates, the electron transfer process reaches a steady state. The steady state current only depends on the size of the electrode.

Interpretation Introduction

(d)

Interpretation:

The time required for the electrode to achieve steady state current following the application of the voltage step should be determined.

Concept introduction:

Current should be used for the calculation is 1.01 x steady state value.

cAx=cA0(1πDt+1r)

cAx - concentration gradient

cA0 - concentration of A

D − diffusion coefficient

t- time after the voltage is applied

r − radius of the sphere

i=nFADcA0(1πDt+1r)

i − time dependent faradaic current

n − number of moles of electrode

F − Faraday constant

A − surface area

D − diffusion coefficient

cA0 - concentration of A

t- time after the voltage is applied

r − radius of the sphere

Interpretation Introduction

(e)

Interpretation:

The calculations should be repeated for a 3 µm spherical platinum electrode and for a spherical iridium electrode with a surface area of 0.785 mm2

Concept introduction:

The formula used:

cAx=cA0(1πDt+1r)

cAx - concentration gradient

cA0 - concentration of A

D − diffusion coefficient

t- time after the voltage is applied

r − radius of the sphere

i=nFADcA0(1πDt+1r)

i − time dependent faradaic current

n − number of moles of electrode

F − Faraday constant

A − surface area

D − diffusion coefficient

cA0 - concentration of A

t- time after the voltage is applied

r − radius of the sphere

Interpretation Introduction

(f)

Interpretation:

The results for the three electrodes should be compared and the differences should be discussed.

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