(a) Interpretation: An equation that relates the desired quantity, mass S 2 - (ng), to the chloridometer readout in mass Cl- (ng) should be derived. Concept introduction: Chloridometer is used in chlorine determination. The number of moles of chloride in an unknown solution can be determined by the following equation. ( n C l − ) u = t u t s × ( n C l − ) s ( n C l − ) u = number of moles of chloride in the unknown sample ( n C l − ) s = number of moles of chloride in the standard sample t u = time required to titrate the unknown chloride solution t s = time required to titrate the standard chloride solution

BuyFind

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 24, Problem 24.13QAP
Interpretation Introduction

(a)

Interpretation:

An equation that relates the desired quantity, mass S2- (ng), to the chloridometer readout in mass Cl- (ng) should be derived.

Concept introduction:

Chloridometer is used in chlorine determination. The number of moles of chloride in an unknown solution can be determined by the following equation.

(nCl)u=tuts×(nCl)s

(nCl)u = number of moles of chloride in the unknown sample

(nCl)s = number of moles of chloride in the standard sample

tu = time required to titrate the unknown chloride solution

ts = time required to titrate the standard chloride solution

Interpretation Introduction

(b)

Interpretation:

Total charge in coulombs required to generate the Ag+ needed to precipitate the sulfide in the standard should be determined.

Concept introduction:

The number of moles can be calculated from mass and molar mass as follows:

n=mM

Here, m is mass and M is molar mass.

Charge of 1 mole of electron transferred = 96485 C

Interpretation Introduction

(c)

Interpretation:

Each of the chloride results should be converted to mass S2- (ng)

Concept introduction:

The number of moles can be calculated from mass and molar mass as follows:

n=mM

Here, m is mass and M is molar mass.

Interpretation Introduction

(d)

Interpretation:

The average mass of S2-, standard deviation, and the % RSD of each standard should be determined.

Concept introduction:

The mean value for mass can be calculated as follows:

X¯=XiN

The standard deviation can be calculated as follows:

s=(xix¯)N1

The value of % RSD can be calculated as follows:

%RSD=sx¯×100

Here, s is a standard deviation and x¯ is mean value.

Interpretation Introduction

(e)

Interpretation:

A plot of the average mass of S2- determined (ng) versus the actual mass (ng) should be prepared. Slope, intercept and standard error and R2 value should be determined.

Concept introduction:

In the plot,

X-axis = actual mass of S2-

Y-axis = determined mass of S2-

Interpretation Introduction

(f)

Interpretation:

The detection limit (ng) and in parts per million using a k factor of 2 should be determined.

Concept introduction:

The minimum distinguishable analytical signal can be calculated as follows:

Sm=S¯bl+ksbl

Here,

Sm - the minimum distinguishable analytical signal

S¯bl - mean blank signal

k − constant

sbl - the standard deviation of the blank signals.

Interpretation Introduction

(g)

Interpretation:

Mass of S2- (ng) in an unknown sample should be determined. The concentration of S2- in parts per million should be determined.

Concept introduction:

The number of moles can be calculated from mass and molar mass as follows:

n=mM

Here, m is mass and M is molar mass.

The concentration can be calculated as follows:

c=nV

Here, n is the number of moles and V is volume.

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