Module 4

Question 1

What is the purpose of a wavelength scan?

Answer 1

Determines the wavelength that a substance maximally absorbs.

Plotted to an absorbance curve.

Question 2

What is Max A?

Answer 2

The wavelength that a substance absorbs the most.

Question 3

What is transmittance?

Answer 3

The proportion of incident light that is transmitted.

Question 4

How is transmittance calculated?

Answer 4

%T = transmitted (Isol)/transmitted (Iorg) x 100%

Question 5

How does concentration relate to light?

Answer 5

Increased concentration results in more light absorbed and less is transmitted.

Question 6

What characteristic of light is measured directly?

Answer 6

Transmittance.

Question 7

How does absorbance relate to concentration and transmittance?

Answer 7

Directly related to concentration.

Inversely related to absorbance.

Question 8

How do you calculate absorbance?

Answer 8

A = 2-log%T

Reported to 3 decimal places.

Question 9

What is Lambert’s Law?

Answer 9

Absorbance is proportional to the distance the light must travel/path length.

Question 10

How does path length affect absorbance?

Answer 10

As path length increases the light absorbed also increases.

Question 11

What represents path length?

Answer 11

Cuvette diameter

Question 12

What is Beer’s Law?

Answer 12

The greater the concentration of absorbing molecules the more light will be absorbed.

Question 13

What wavelength produces the best linearity between concentration and absorption?

Answer 13

Max A

Question 14

What is the Beer-Lambert/Beer’s Law?

Answer 14

Absorbance is proportional to the product of concentration, depth of solution and a constant.

Question 15

How is absorbance calculated using Beer’s Law?

Answer 15

A = a x b x c

a = absorptivity

A = E x b x c

E = molar absorptivity

Question 16

How is Beer’s Law plotted?

Answer 16

Concentration x-axis

Absorption y-axis

Question 17

What deviations in absorbance readings are due to method/operator?

Answer 17

Incorrect wavelength

High analyze concentration

Unmatched cuvettes

Failure to set 0%T/100%T properly

Failure to maintain pH and temp

Impurities or turbidity

Interfering substances that absorb the same wavelengths

Question 18

What deviations in absorbance readings are due to instrument error?

Answer 18

Stray light

Inability to select a narrow band of wavelengths

Line voltage fluctuations

Unstable light source

Nonlinear detector response

Question 19

How can Beer’s law be used for quantitative analysis?

Answer 19

Calculate the unknown concentration by comparing its absorbance to a standard.

Making a calibration curve of known standards that can be used to determine the unknown concentration.

Question 20

When can a concentration be calculated by comparing absorbances?

Answer 20

If:
Beer’s law is obeyed

Using A

Setting the blank at 0A

The standard is close in concentration to the unknown

The standard and unknown are analyzed at the same time

Question 21

How are the unknown and standard concentrations related?

Answer 21

Au/As = Cu/Cs

Question 22

How does wavelength relate to substance characteristics?

Answer 22

The wavelengths transmitted and absorbed result in unique colour properties.

Allows for detection and quantification of substances.

Transmitted and absorbed colours are complimentary.