Objectives and Materials

According to the simulation objectives, which task directly demonstrates the relationship predicted by Beer’s Law?

• Calculating transmittance for a single solution at one wavelength

• Creating a graph of absorbance versus concentration across several solutions

• Listing the components of a spectrophotometer

• Measuring absorbance without changing solution concentration

According to the procedure, which action ensures the detector is correctly positioned relative to the selected wavelength during the Beer's Law simulation?

• Place the detector at the far end of the bench away from the cuvette

• Align the middle of the detector so it coincides with the wavelength

• Set the detector to transmittance mode before changing concentration

• Increase the cuvette length until the detector reading stabilizes

In the Beer's Law simulation workflow described, what should you record at least 10 times while increasing solution concentration?

• Only absorbance values

• Only transmittance values

• Both absorbance and transmittance values

• Detector position measurements

A student uses the interface shown to determine molar absorptivity (b). Which strategic plan best uses evidence from the simulation to compute b?

• Keep concentration fixed, vary wavelength randomly, and average absorbance readings

• Collect paired absorbance and concentration data at a fixed path length and appropriate preset wavelength, plot absorbance vs. concentration, and obtain b from the slope

• Measure transmittance at multiple detector positions and take the highest value as b

• Increase cuvette length stepwise without recording concentration and use the final absorbance reading as b

Beer–Lambert Law: A = ε c l. Which variable is defined as the amount of light absorbed by the sample at a specific wavelength?

• ε, molar absorptivity

• A, absorbance

• c, concentration

• l, path length

A solution shows an absorbance of 0.80 in a 1.00 cm cuvette. The concentration of the absorbing solute is 0.0200 M. Using the Beer–Lambert relationship, what is the molar absorptivity ε of the solute? Use ε = A/(c × l).

• 2.00 L mol⁻¹ cm⁻¹

• 40.0 L mol⁻¹ cm⁻¹

• 0.0400 L mol⁻¹ cm⁻¹

• 0.800 L mol⁻¹ cm⁻¹

According to Beer's Law, how does the presence of a more colored or more concentrated substance in a solution affect light passing through it? Choose the best statement.

• It allows more light to pass because particles scatter light away.

• It reduces the amount of light that passes as darker, concentrated solutions absorb more.

• It has no effect on light transmission because absorbance depends only on wavelength.

• It increases transmittance while decreasing absorbance for darker solutions.

Which statement best describes the relationship between absorbance and transmittance as defined in spectrophotometry?

• They increase together because both measure light entering the sample.

• They are unrelated; absorbance is chemical while transmittance is physical.

• They vary inversely; when absorbance increases, transmittance decreases.

• They are equal at the solution’s maximum absorbance (λmax).

A solution shows its highest absorbance at a particular wavelength called λmax. Which factor primarily explains why λmax changes when the solution is changed?

• Instrument calibration varies each run, shifting λmax randomly.

• Each substance has a distinct color, composition, and electronic structure that determine which wavelengths it absorbs most strongly.

• Ambient room light alters the spectrophotometer’s lamp output causing different λmax values.

• Path length alone determines λmax since it controls how far light travels.

Using Beer–Lambert Law (A = ε c l), what happens to absorbance and transmittance when the path length l is doubled while c and ε remain constant?

• Absorbance decreases and transmittance increases because light travels a shorter distance.

• Absorbance increases and transmittance decreases due to more interaction with absorbing particles.

• Both absorbance and transmittance increase proportionally with path length.

• Absorbance is unchanged while transmittance decreases because ε controls absorption.