AP Chemistry: Beer's Law

What is the Beer's Law equation?

• A = εbc

• A = ε²bc

• A = εcb²

• A = εbc²

Define absorbance and transmittance in the context of Beer's Law.

• Absorbance is a measure of how much light is absorbed by a sample, while transmittance is the fraction of light that passes through a sample without being absorbed.

• Absorbance is a measure of how much light is emitted by a sample, while transmittance is the fraction of light that passes through a sample without being absorbed.

• Absorbance is a measure of how much light is scattered by a sample, while transmittance is the fraction of light that passes through a sample without being absorbed.

• Absorbance is a measure of how much light is reflected by a sample, while transmittance is the fraction of light that passes through a sample without being absorbed.

What is molar absorptivity?

• Molar absorptivity is a measure of how strongly a substance absorbs light at a specific wavelength.

• Molar absorptivity is a measure of how weakly a substance absorbs light at a specific wavelength.

• Molar absorptivity is a measure of how strongly a substance reflects light at a specific wavelength.

• Molar absorptivity is a measure of how strongly a substance emits light at a specific wavelength.

How do you calculate concentration using Beer's Law?

• C = ε/Ab

• C = A/bc

• C = εbA

• C = A/εb

What are some applications of Beer's Law?

• Quantitative analysis, determination of concentration, measurement of absorbance and transmittance, studying chromophores and complex molecules

• Determining the temperature of a solution, Identifying the pH of a solution, Measuring the viscosity of a liquid

What is the mathematical relationship between absorbance and concentration in Beer's Law?

• Absorbance is directly proportional to concentration.

• Absorbance and concentration have no relationship.

• Absorbance increases exponentially with concentration.

• Absorbance is inversely proportional to concentration.

Explain the concept of path length in Beer's Law.

• The concept of path length in Beer's Law is the distance that light travels through a sample.

• The concept of path length in Beer's Law is the concentration of the sample.

• The concept of path length in Beer's Law is the temperature of the sample.

• The concept of path length in Beer's Law is the amount of liquid in the sample.

What are the units of molar absorptivity?

• liters per mole per centimeter

• liters per mole per meter

• moles per liter per centimeter

• grams per mole per centimeter

How does Beer's Law help in determining the concentration of unknown solutions?

• Beer's Law helps in determining the concentration of unknown solutions by measuring the volume of the solution.

• Beer's Law helps in determining the concentration of unknown solutions by analyzing the color of the solution.

• Beer's Law helps in determining the concentration of unknown solutions by measuring the temperature of the solution.

• Beer's Law helps in determining the concentration of unknown solutions by measuring the absorbance of the solution and comparing it to a calibration curve of known concentrations.

The diagrams above show the ultraviolet absorption spectra for two compounds. Diagram 1 is the absorption spectrum of pure acetone, a solvent used when preparing solutions for an experiment. Diagram 2 is the absorption spectrum of the solute for which the absorbance needs to be measured to determine its concentration. When the student reads the absorbance of the solution at 280nm, the result is too high. Which of the following is most likely responsible for the error in the measured absorbance?

• The student added too little solute to the acetone before measuring its absorbance.

• The student rinsed the cuvette with the solution before filling the cuvette with the solution.

• The student forgot to calibrate the spectrophotometer first by using a cuvette containing only acetone.

• The wavelength setting was accidentally changed from 280nm to 300nm before the student made the measurement.