Solucionarios de skoog

Skoog/Holler/Crouch
Principles of Instrumental Analysis, 6th ed.

Chapter 1
Instructor’s Manual

CHAPTER 1
1-1.

A transducer is a device that converts chemical or physical information into an electrical
signal or the reverse. The most common input transducers convert chemical or physical
information into a current, voltage, or charge, and the most common output transducers
convertelectrical signals into some numerical form.

1-2.

The information processor in a visual color measuring system is the human brain.

1-3.

The detector in a spectrograph is a photographic film or plate.

1-4.

Smoke detectors are of two types: photodetectors and ionization detectors. The
photodetectors consist of a light source, such as a light-emitting diode (LED) and a
photodiode toproduce a current proportional to the intensity of light from the LED.
When smoke enters the space between the LED and the photodiode, the photocurrent
decreases, which sets off an alarm. In this case the photodiode is the transducer.
In ionization detectors, which are the typical battery-powered detectors found in homes, a
small radioactive source (usually Americium) ionizes the air betweena pair of electrodes.
When smoke enters the space between the electrodes, the conductivity of the ionized air
changes, which causes the alarm to sound. The transducer in this type of smoke detector
is the pair of electrodes and the air between them.

1-5.

A data domain is one of the modes in which data may be encoded. Examples of data
domain classes are the analog, digital and timedomains. Examples of data domains are
voltage, current, charge, frequency, period, number.

1

Principles of Instrumental Analysis, 6th ed.
1-6.

Chapter 1

Analog signals include voltage, current, charge, and power. The information is encoded
in the amplitude of the signal.

1-7.
Output Transducer
LCD display
Computer monitor

Use
Alphanumeric information
Alphanumeric information,text,
graphics
Alphanumeric and graphical
information
Rotates to change position of
attached elements

Laser printer
Motor

1-8.

A figure of merit is a number that provides quantitative information about some
performance criterion for an instrument or method.

1-9.

Let cs= molar concentration of Cu2+ in standard = 0.0287 M
cx = unknown Cu2+ concentration
Vs = volume ofstandard = 0.500 mL
Vx = volume of unknown = 25.0 mL
S1 = signal for unknown = 23.6
S2 = signal for unknown plus standard = 37.9
Assuming the signal is proportional to cx and cs , we can write
S1 = Kcx or

K = S1/cx

After adding the standard

⎛ V c + Vs cs ⎞
S2 = K ⎜ x x
⎟
⎝ Vx + Vs ⎠
Substituting for K and rearranging gives,
cx =

S1Vs cs
S 2 (Vx + Vs ) − S1Vx

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Principles ofInstrumental Analysis, 6th ed.

cx =

Chapter 1

23.6 × 0.500 mL × 0.0287 M
= 9.00 × 10−4 M
37.9(0.500 mL + 25.0 mL) − (23.6 × 25.0 mL)

1-10. The results are shown in the spreadsheet below.

(a)

Slope, m = 0.0701, intercept, b = 0.0083

(b)

From LINEST results, SD slope, sm = 0.0007, SD intercept, sb = 0.0040

(c)

95% CI for slope m is m ± tsm where t is the Student tvalue for 95% probability and N –
2 = 4 degrees of freedom = 2.78
95% CI for m = 0.0701 ± 2.78 × 0.0007 = 0.0701 ± 0.0019 or 0.070 ± 0.002
For intercept, 95% CI = b ± tsb = 0.0083 ± 2.78 × 0.004 = 0.0083 ± 0.011 or 0.08 ± 0.01

(d)

cu = 4.87 ± 0.086 mM or 4.87 ± 0.09 mM
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Principles of Instrumental Analysis, 6th ed.

Chapter 1

1-11. The spreadsheet below gives the results

(a)See plot in spreadsheet.

(b)

cu = 0.410 μg/mL

(c)

S = 3.16Vs + 3.25

(d)

cu =

(e)

From the spreadsheet sc = 0.002496 or 0.002 μg/mL

bcs
3.246 × 2.000 μg/mL
=
= 0.410 μg/mL
mVu 3.164 mL−1 × 5.00 mL

4

Skoog/Holler/Crouch
Principles of Instrumental Analysis, 6th ed.

Chapter 2
Instructor’s Manual

CHAPTER 2
2-1.

(a) Applying the voltage divider...