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 convert electrical signals into some numerical form. 1-2. 1-3. 1-4. The information processor in a visual color measuring system is the human brain. The detector in a spectrograph is a photographic film or plate. 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 to produce 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 between a 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 time domains. 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 Laser printer Motor Use Alphanumeric information Alphanumeric information, text, graphics Alphanumeric and graphical information Rotates to change position of attached elements

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 of standard = 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

2

Principles of Instrumental Analysis, 6th ed.

Chapter 1

cx =

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) (b) (c)

Slope, m = 0.0701, intercept, b = 0.0083 From LINEST results, SD slope, sm = 0.0007, SD intercept, sb = 0.0040 95% CI for slope m is m ± tsm where t is the Student t value 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. 1-11. The spreadsheet below gives the results

Chapter 1

(a) (b) (c) (d) (e)

See plot in spreadsheet.

cu = 0.410 μg/mL S = 3.16Vs + 3.25

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

From the spreadsheet sc = 0.002496 or 0.002 μg/mL

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

Chapter 2 Instructor’s Manual

CHAPTER 2

2-1. (a) Applying the voltage divider equation (2-10)

1.0 R1 = 10 R1 + R2 + R3 4.0 R2 = 10 R1 + R2 + R3

V3 = 10.0V – 1.0 V – 4.0 V = 5.0 V

R3 5.0 = 10 R1 + R2 + R3...