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What does Beer’s Law state about absorbance?
What does Beer’s Law state about absorbance?
What is the purpose of the blank in spectrophotometric analysis?
What is the purpose of the blank in spectrophotometric analysis?
At which wavelength is λmax selected for analysis?
At which wavelength is λmax selected for analysis?
Which of the following best describes a standard curve or calibration curve?
Which of the following best describes a standard curve or calibration curve?
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What may happen to the absorbance of a solution when it is diluted?
What may happen to the absorbance of a solution when it is diluted?
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In the procedure, which solution is identified as the blank?
In the procedure, which solution is identified as the blank?
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Which statement about λmax is true?
Which statement about λmax is true?
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What is the appropriate action when preparing a blank cuvette?
What is the appropriate action when preparing a blank cuvette?
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What does the term 'absorbance' refer to in spectrophotometric analysis?
What does the term 'absorbance' refer to in spectrophotometric analysis?
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Which of the following equations correctly defines transmittance?
Which of the following equations correctly defines transmittance?
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What principle does the Beer Lambert law illustrate?
What principle does the Beer Lambert law illustrate?
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Which component of a spectrophotometer is responsible for measuring light intensity?
Which component of a spectrophotometer is responsible for measuring light intensity?
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The equation E = hν = hc/λ expresses the relationship between what concepts?
The equation E = hν = hc/λ expresses the relationship between what concepts?
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In the context of Beer Lambert law, which unit is used to express molar absorptivity when concentration is in moles per liter?
In the context of Beer Lambert law, which unit is used to express molar absorptivity when concentration is in moles per liter?
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What is the role of the prism or grating in a spectrophotometer?
What is the role of the prism or grating in a spectrophotometer?
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What is typically measured by using a spectrophotometer in spectrophotometric analysis?
What is typically measured by using a spectrophotometer in spectrophotometric analysis?
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What is the first step when using a spectrophotometer for analysis?
What is the first step when using a spectrophotometer for analysis?
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What is the definition of λmax in spectrophotometric analysis?
What is the definition of λmax in spectrophotometric analysis?
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If tube #1 contains 1 ml of CoCl2.6H2O and 4 ml of distilled water, what is its concentration?
If tube #1 contains 1 ml of CoCl2.6H2O and 4 ml of distilled water, what is its concentration?
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At what absorbance value was λmax determined to be 500 nm?
At what absorbance value was λmax determined to be 500 nm?
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What is the purpose of measuring absorbance at various dilutions of CoCl2.6H2O?
What is the purpose of measuring absorbance at various dilutions of CoCl2.6H2O?
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Which tube results in the highest absorbance reading?
Which tube results in the highest absorbance reading?
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What should be done after preparing the blank cuvette?
What should be done after preparing the blank cuvette?
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What does the term 'transmittance' refer to in spectrophotometry?
What does the term 'transmittance' refer to in spectrophotometry?
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What is the formula for Beer’s Law?
What is the formula for Beer’s Law?
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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?
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?
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What concentration (C) of CoCl2.6H2O corresponds to an absorbance (A) of 0.456 using Beer’s law?
What concentration (C) of CoCl2.6H2O corresponds to an absorbance (A) of 0.456 using Beer’s law?
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In the context of the calibration curve, what does the R² value of 0.9999 indicate?
In the context of the calibration curve, what does the R² value of 0.9999 indicate?
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Which method describes the process of using a graph to find the concentration from absorbance?
Which method describes the process of using a graph to find the concentration from absorbance?
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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
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Absorbance is linearly related to the concentration of the absorbing substance.
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A = abc, where:
- a (ε) is the absorptivity (or extinction coefficient)
- b is the path length of the sample
- c is the concentration
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Beer-Lambert's law applies to dilute solutions.
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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.
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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.
