Experiment 3: Spectrophotometric Analysis
29 Questions
1 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to Lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What does Beer’s Law state about absorbance?

  • Absorbance is independent of the concentration.
  • Absorbance increases with temperature.
  • Absorbance is proportional to concentration. (correct)
  • Absorbance is inversely proportional to concentration.

What is the purpose of the blank in spectrophotometric analysis?

  • To increase the absorbance of the analyte.
  • To provide a standard curve.
  • To act as the main absorbent species.
  • To correct for absorbance measured excluding the analyte. (correct)

At which wavelength is λmax selected for analysis?

  • The wavelength that is the lowest value.
  • The wavelength with maximum absorbance. (correct)
  • The wavelength at which the solution is colorless.
  • The wavelength where absorbance is zero.

Which of the following best describes a standard curve or calibration curve?

<p>A linear plot of absorbance versus concentration for standard solutions. (A)</p> Signup and view all the answers

What may happen to the absorbance of a solution when it is diluted?

<p>The absorbance decreases. (C)</p> Signup and view all the answers

In the procedure, which solution is identified as the blank?

<p>Distilled water. (D)</p> Signup and view all the answers

Which statement about λmax is true?

<p>λmax is constant for a specific substance at a specific wavelength. (D)</p> Signup and view all the answers

What is the appropriate action when preparing a blank cuvette?

<p>Fill it with distilled water and clean the outer surfaces. (B)</p> Signup and view all the answers

What does the term 'absorbance' refer to in spectrophotometric analysis?

<p>The intensity of the light after passing through the solution (B)</p> Signup and view all the answers

Which of the following equations correctly defines transmittance?

<p>T = Pt/P0 (B)</p> Signup and view all the answers

What principle does the Beer Lambert law illustrate?

<p>Absorbance is directly proportional to the analyte's concentration (B)</p> Signup and view all the answers

Which component of a spectrophotometer is responsible for measuring light intensity?

<p>Photoelectric cell (D)</p> Signup and view all the answers

The equation E = hν = hc/λ expresses the relationship between what concepts?

<p>Energy, frequency, and wavelength (C)</p> Signup and view all the answers

In the context of Beer Lambert law, which unit is used to express molar absorptivity when concentration is in moles per liter?

<p>cm-1 M-1 (C)</p> Signup and view all the answers

What is the role of the prism or grating in a spectrophotometer?

<p>To separate light into its component wavelengths (C)</p> Signup and view all the answers

What is typically measured by using a spectrophotometer in spectrophotometric analysis?

<p>Concentration of a solution (B)</p> Signup and view all the answers

What is the first step when using a spectrophotometer for analysis?

<p>Set the absorbance of the blank cuvette to 0 (D)</p> Signup and view all the answers

What is the definition of λmax in spectrophotometric analysis?

<p>The wavelength with the highest absorbance (A)</p> Signup and view all the answers

If tube #1 contains 1 ml of CoCl2.6H2O and 4 ml of distilled water, what is its concentration?

<p>0.03M (B)</p> Signup and view all the answers

At what absorbance value was λmax determined to be 500 nm?

<p>0.644 (D)</p> Signup and view all the answers

What is the purpose of measuring absorbance at various dilutions of CoCl2.6H2O?

<p>To find the concentration of unknown solutions (D)</p> Signup and view all the answers

Which tube results in the highest absorbance reading?

<p>Tube #5 (A)</p> Signup and view all the answers

What should be done after preparing the blank cuvette?

<p>Measure the absorbance of the CoCl2 solutions (D)</p> Signup and view all the answers

What does the term 'transmittance' refer to in spectrophotometry?

<p>The ratio of light passing through the solution (B)</p> Signup and view all the answers

What is the formula for Beer’s Law?

<p>A = abC (A)</p> Signup and view all the answers

If the slope (K) obtained from the calibration curve is 5.55 M$^{-1}$, what is the molar absorptivity 'a' when the path length 'b' is 1 cm?

<p>5.55 M$^{-1}$cm$^{-1}$ (C)</p> Signup and view all the answers

What concentration (C) of CoCl2.6H2O corresponds to an absorbance (A) of 0.456 using Beer’s law?

<p>0.0821 M (D)</p> Signup and view all the answers

In the context of the calibration curve, what does the R² value of 0.9999 indicate?

<p>A strong correlation (C)</p> Signup and view all the answers

Which method describes the process of using a graph to find the concentration from absorbance?

<p>Graphical determination (A)</p> Signup and view all the answers

Flashcards

Spectrophotometric Analysis

A method to determine the concentration of a solution by measuring how much electromagnetic radiation is absorbed.

Transmittance (T)

The ratio of the light power exiting a sample to the incident light power. Expressed as a percentage.

Absorbance (A)

A measure of how much light is absorbed by a sample. Calculated from transmittance.

Beer-Lambert Law

The absorbance of a solution is directly proportional to the concentration of the solution.

Signup and view all the flashcards

Electromagnetic Radiation

A form of energy that has both wave-like and particle-like properties.

Signup and view all the flashcards

Spectrophotometer

An instrument used to measure the absorption or transmission of light through a solution.

Signup and view all the flashcards

Absorptivity/Molar Absorptivity

A value that describes how strongly a substance absorbs light. It's dependent on the concentration per unit of length.

Signup and view all the flashcards

Concentration

The amount of substance (analyte) in a given volume of solution.

Signup and view all the flashcards

Absorbance Blank

A solution used to correct for background absorbance in a sample.

Signup and view all the flashcards

Absorption Spectrum

Graph of absorbance vs. wavelength for a solution.

Signup and view all the flashcards

λmax

The wavelength at which a substance absorbs light most strongly.

Signup and view all the flashcards

Calibration Curve

Graph of absorbance vs. concentration of a substance.

Signup and view all the flashcards

Dilute Solution

A solution with a low concentration of solute.

Signup and view all the flashcards

Standard Curve

A graph of concentration of a known solution versus the absorbance.

Signup and view all the flashcards

Blank Solution

A solution containing all components of the sample except the analyte.

Signup and view all the flashcards

Beer's Law

States that the absorbance of a solution is directly proportional to the concentration of the analyte and the path length of the light beam through the solution.

Signup and view all the flashcards

Beer's Constant (K)

A proportionality constant in Beer's Law that relates the absorbance of a solution to its concentration. It is also known as the molar absorptivity (a) multiplied by the path length (b).

Signup and view all the flashcards

Molar Absorptivity (a)

The inherent ability of a substance to absorb light at a specific wavelength. It's a constant specific to the substance and wavelength.

Signup and view all the flashcards

Calculate concentration from absorbance

Using Beer's Law (A=abC) and knowing the molar absorptivity (a) and path length (b), you can calculate the concentration (C) of an unknown solution by measuring its absorbance (A).

Signup and view all the flashcards

Creating a calibration curve

A plot of absorbance (y-axis) against concentration (x-axis). It's used to determine unknown concentrations by measuring absorbance and finding the corresponding concentration on the curve.

Signup and view all the flashcards

What is λmax?

The wavelength at which a substance absorbs the most light, leading to the highest absorbance value.

Signup and view all the flashcards

How do you determine λmax?

By measuring the absorbance of a solution at different wavelengths and plotting the data on a graph, the wavelength corresponding to the highest absorbance value is λmax.

Signup and view all the flashcards

Why is λmax important?

It is used for accurate concentration measurements in spectrophotometric analysis, as it gives the most sensitive response for the substance being analyzed.

Signup and view all the flashcards

How does dilution affect absorbance?

As the concentration of a solution decreases (dilution), the absorbance also decreases because fewer molecules are available to absorb light.

Signup and view all the flashcards

What's the purpose of a blank solution?

A blank solution containing all components of the sample except the analyte is used to calibrate the spectrophotometer to zero absorbance and account for any background absorbance.

Signup and view all the flashcards

How do you use Beer-Lambert Law for analysis?

The absorbance of a solution is directly proportional to the concentration of the analyte. Using a standard curve (concentration vs. absorbance), the concentration of an unknown sample can be determined by measuring its absorbance.

Signup and view all the flashcards

What's the relationship between concentration and absorbance?

They are directly proportional, meaning as concentration increases, absorbance also increases.

Signup and view all the flashcards

What is a standard curve?

A graph plotted with the known concentrations of solutions against their corresponding absorbance values. It serves as a reference for determining the concentration of an unknown sample by comparing its absorbance to the curve.

Signup and view all the flashcards

Study Notes

Experiment 3: Spectrophotometric Analysis

  • The experiment involves analyzing the absorption spectrum of Cobalt (II) Chloride using spectrophotometry.
  • Spectrophotometry measures the attenuation of electromagnetic radiation passing through a sample to determine its concentration.

Theory

  • Spectrophotometric analysis relies on the attenuation of electromagnetic radiation.
  • Solutions are analyzed by measuring the transmission or absorbance of light through them.
  • This analysis determines the concentration.

Electromagnetic Radiation

  • Electromagnetic radiation is a form of energy with wave-particle duality.
  • It can be described in terms of wavelength or frequency.
  • The energy of radiation is expressed as E = hv = hc/λ, where h is Planck's constant, v is frequency, c is the speed of light, and λ is wavelength.

Spectrophotometer

  • A spectrophotometer is used to measure absorbance.
  • The spectrophotometer separates light into its component wavelengths.
  • It selectively measures the intensity of specific wavelengths of light after passing through the sample solution.
  • All spectrophotometers have a light source, a monochromator to isolate the desired wavelength, a sample holder, and a detector (photoelectric cell).

Transmittance

  • Transmittance (T) is the ratio of the electromagnetic power exiting the sample to the incident power.
  • T = Pt/P0, where Pt is the transmitted power and P0 is the incident power.

Absorbance

  • Absorbance (A) is a common measurement for attenuation.
  • A = -log T = -log (Pt/P0) = log (P0/Pt)

Beer-Lambert Law

  • Absorbance is linearly related to the concentration of the absorbing substance.

  • A = abc, where:

    • a (ε) is the absorptivity (or extinction coefficient)
    • b is the path length of the sample
    • c is the concentration

  • Beer-Lambert's law applies to dilute solutions.

  • To ensure accuracy, dilution of the solution may be necessary before completing an analysis.

Blank

  • A blank is used to correct for any absorbance from components other than the analyte.
  • The blank solution contains all components of the sample matrix except the analyte.
  • In this experiment, distilled water serves as the blank.

Absorption Spectrum and λmax

  • The absorption spectrum graphs absorbance versus wavelength.
  • When an analyte is the major absorbing species, it is possible to measure an absorption spectrum.
  • λmax is the wavelength at which the maximum absorbance occurs, and this value remains constant upon dilution.
  • This value is a characteristic of a particular solution.

Calibration Curve

  • A calibration curve plots absorbance versus analyte concentration for standard solutions.
  • The relationship between the absorbance and concentration is linear.

Procedure

  • The procedure involves preparing standard solutions of Cobalt (II) Chloride.
  • The procedure also includes measuring the absorbance of the prepared solutions and an unknown sample at specific wavelengths (usually λmax).
  • The blank (distilled water) is used in the spectrophotometer to calibrate it to zero absorbance or 100% transmittance.

Data Analysis

  • The generated data allows determination of the maximum wavelength (λmax) and the Beer's Law constant (K).
  • These values are used to calculate the concentration of unknown samples using the Beer-Lambert law.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Quiz Team

Related Documents

Absorption Spectrum of CoCl2.6H2O PDF

Description

This quiz covers the spectrophotometric analysis of Cobalt (II) Chloride. It challenges your understanding of electromagnetic radiation, absorbance, and the principles of using a spectrophotometer. Test your knowledge of how light interacts with solutions and its importance in determining concentration.

More Like This

Use Quizgecko on...
Browser
Open
Browser
Browser