Colorimetry and Chromatography Quiz
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Questions and Answers

Which of the following statements about Colorimetry is true?

  • Colorimetry can be used to estimate the concentration of a colored solution. (correct)
  • The intensity of color in a solution is unrelated to the concentration of the colored species.
  • Colorimetry can only analyze colorless solutions.
  • Colorimetry requires a complex and expensive setup.

    • A Colourimeter can determine the concentration of a solution even when it is colorless.

    False

    What does a Colourimeter measure in a solution?

    The amount of light absorbed by the solution.

    In colorimetry, if a solution is blue, it absorbs _____ light.

    <p>red</p> Signup and view all the answers

    Match the components of a Colourimeter with their function:

    <p>Light Emitting Diodes (LEDs) = Provide light of specific wavelengths Cuvet = Holds the solution to be tested Detector = Measures the amount of light absorbed Zero adjustment = Factors out absorbance of the solvent</p> Signup and view all the answers

    What type of chromatography uses high pressure to elute a mixture?

    <p>High Performance Liquid Chromatography (HPLC)</p> Signup and view all the answers

    Ethanol concentration can be determined using a calibration graph.

    <p>True</p> Signup and view all the answers

    What is the pressure typically used in High Performance Liquid Chromatography?

    <p>4000 psi</p> Signup and view all the answers

    In chromatography, the _____ phase can be altered to create different bonding properties.

    <p>stationary</p> Signup and view all the answers

    Match the following stationary phases with their descriptions:

    <p>Normal Polarity = Interacts with polar molecules using polar sites Reverse Polarity = Has non-polar characteristics Ion Exchange = Separates ions based on charge Size Exclusion = Separates molecules based on size</p> Signup and view all the answers

    In increasing order of polarity, which component elutes first in normal polarity chromatography?

    <p>Non-polar molecules</p> Signup and view all the answers

    A solvent peak is typically not seen when a solid component is dissolved in solvent.

    <p>False</p> Signup and view all the answers

    What is one of the substances that can be used in the stationary phase for normal polarity?

    <p>Silica</p> Signup and view all the answers

    What component in carrots is responsible for their orange color?

    <p>Carotene</p> Signup and view all the answers

    The UV-visible spectrum includes wavelengths between approximately 400 nm and 750 nm.

    <p>True</p> Signup and view all the answers

    What is the molecular formula of beta-Carotene?

    <p>C40H56</p> Signup and view all the answers

    In UV-visible spectroscopy, the _______ blank is used to set absorbance to 0%.

    <p>solvent</p> Signup and view all the answers

    Match the following characteristics with carotene:

    <p>Molecular formula = C40H56 Molar Mass = 537 Melting Point = 178-179 °C Occurs in = Chromoplasts of plants</p> Signup and view all the answers

    What happens to large molecules when using gel beads in chromatography?

    <p>They elute quickly due to restricted path</p> Signup and view all the answers

    All light waves travel at different speeds in a vacuum.

    <p>False</p> Signup and view all the answers

    What is the process called when low energy electrons absorb energy to move to higher energy levels?

    <p>Absorption</p> Signup and view all the answers

    Excited electrons return to lower energy states during ______.

    <p>Emission</p> Signup and view all the answers

    What is the relationship between light absorption and the concentration of an absorbing component?

    <p>Light absorption is directly proportional to concentration</p> Signup and view all the answers

    Emission spectra are characterized by continuous energy emission.

    <p>False</p> Signup and view all the answers

    Match the following terms with their definitions:

    <p>Absorption = Low energy electrons move to a higher energy level Emission = Electrons return to lower energy levels releasing energy Excited State = State of an electron after absorbing energy Ground State = Lowest energy state of an electron</p> Signup and view all the answers

    What are the regions of the electromagnetic spectrum based on?

    <p>Frequency and wavelength</p> Signup and view all the answers

    What does Atomic Absorption Spectrometry primarily measure?

    <p>Small concentrations of metal ions in solution</p> Signup and view all the answers

    Atomic Absorption Spectrometry can detect concentrations as small as parts per million (ppm).

    <p>False</p> Signup and view all the answers

    List two applications of Atomic Absorption Spectrometry in industry.

    <p>Quality control of metals in steel and testing water for metal ions.</p> Signup and view all the answers

    The ____ is a key component that emits unique wavelengths of light in an Atomic Absorption Spectrometer.

    <p>Hollow Cathode Lamp</p> Signup and view all the answers

    Match the following metals with their respective symbol:

    <p>Aluminum = Al Arsenic = As Copper = Cu Zinc = Zn</p> Signup and view all the answers

    Which part of the Atomic Absorption Spectrometer is responsible for isolating specific wavelengths?

    <p>Monochromator</p> Signup and view all the answers

    Another species absorbing at the same wavelength can be a source of error in AAS.

    <p>True</p> Signup and view all the answers

    What is one advantage of using Atomic Absorption Spectroscopy?

    <p>It is highly specific to the metal ion being analyzed.</p> Signup and view all the answers

    In a C18 phase stationary phase, which type of molecules interact strongly with the polar sites capped with non-polar groups?

    <p>Non-polar molecules</p> Signup and view all the answers

    Silica in anion exchange phases is substituted with cationic residues that interact with cationic species.

    <p>False</p> Signup and view all the answers

    What type of charged species does the cation exchange stationary phase primarily interact with?

    <p>Cationic species</p> Signup and view all the answers

    In size exclusion chromatography, separation is based on ______ size.

    <p>molecular</p> Signup and view all the answers

    Match the type of stationary phase with its primary characteristic:

    <p>C18 Phase = Interacts with non-polar molecules Cation Exchange = Interacts with cationic species Anion Exchange = Interacts with anionic species Size Exclusion = Separates based on molecular size</p> Signup and view all the answers

    What is the order of elution in a phase with non-polar sites?

    <p>Most non-polar to least non-polar</p> Signup and view all the answers

    Anionic species are later eluted with base solutions in anionic exchange.

    <p>False</p> Signup and view all the answers

    What type of solution is used to elute cationic species in cation exchange?

    <p>Acid (H+)</p> Signup and view all the answers

    In an anion exchange system, the most ______ species adhere to the support.

    <p>negative (−ve)</p> Signup and view all the answers

    What type of interaction does silica have in size exclusion chromatography?

    <p>Size-based interactions</p> Signup and view all the answers

    Study Notes

    Instrumental Analytical Techniques

    • These techniques utilize chromatography and spectroscopy to analyze components in mixtures.

    Chromatographic Techniques

    • Thin-layer chromatography (TLC)
    • Column chromatography
    • Gas chromatography (GC)
    • High-performance liquid chromatography (HPLC)

    Spectroscopic Techniques

    • Atomic absorption spectroscopy (AAS)
    • Colorimetry
    • UV-Visible Spectroscopy (UV-Vis)

    Chromatography

    • A technique that separates components in a mixture by exploiting interactions with a stationary phase and a mobile phase (solvent).
    • Components separate based on different adsorption levels to the stationary phase and solubility in the mobile phase.

    Types of Chromatography

    • Paper Chromatography
    • Thin-Layer Chromatography (TLC)
    • Column Chromatography
    • Gas-Liquid Chromatography (GLC)
    • High-Performance Liquid Chromatography (HPLC)

    Thin-Layer (and Paper) Chromatography

    • TLC plates use inert supports (e.g., glass, plastic, aluminum) coated with a thin layer of chromatographic media (e.g., silica).
    • Sample is applied to the bottom of the plate (origin).
    • Solvent is added to the plate, moving the sample up the plate through adsorption.
    • Rf value is calculated as the ratio of the distance travelled by a component to the distance travelled by the solvent front.

    Thin Layer and Paper Chromatography

    • Applies a mixture solution as a spot or band at the bottom of a plate.
    • The mixture travels with the solvent up the plate.
    • Comparing standards to determine the unknown solution.

    Column Chromatography

    • A solvent elutes a mixture through a column with a solid support (e.g., silica).
    • Separation occurs as components move at different rates through the medium.

    Gas-Liquid Chromatography (GLC)

    • Injects a sample (gas or liquid) into a thin, steel-jacketed column.
    • The column contains a stationary phase (dense liquid) on a solid support.
    • Components vaporize and travel through the column at varying rates, based on their interactions with the stationary phase.
    • A detector measures the components as they exit the column.

    Gas Chromatogram of High-Grade Petrol

    • Different hydrocarbon components are identified by their retention time (time taken to travel from the injection point to the detector) in the column.

    Qualitative Analysis in Chromatography

    • Identify components in a mixture by comparing their Rf values with known standards.
    • Helps understand the composition of a mixture (e.g., food sample).

    Quantitative Analysis in Chromatography

    • Use a calibration graph of known concentrations (plotting absorption versus concentration) to find the unknown concentration within a sample.

    Spectroscopy

    • Uses absorption and emission of electromagnetic radiation by atoms to identify and determine the concentration of components.
    • Electrons absorb energy and move to higher energy levels and consequently release energy when returning to lower energy levels.

    Absorption Spectroscopy

    • Light absorbed (absorption) is proportionally related to the concentration of the absorbing component; this is the basis for quantitative measurements.

    Colorimetry

    • Colorimetry is a quantitative technique using the intensity of a solution’s color to determine concentration.
    • Color is directly related to the concentration of colored species within the mixture.
    • Works for colored or chemically colored substances.
    • Standards are measured to find an unknown concentration visually or instruments.

    Atomic Absorption Spectroscopy (AAS)

    • Measures small metal ion concentrations in a solution.
    • Used in industry for analyzing ores, controlling metal quality in steel, and assessing metals in water and food.
    • Different wavelengths are absorbed by different metal ions.

    Advantages of AAS

    • High sensitivity: detects very low concentrations (e.g., parts per billion).
    • High specificity: measures a specific metal ion without interference from other components.

    UV-Visible Spectroscopy

    • Measures the absorbed energy of a sample.
    • Suitable for colored substances or substances that can be colored through a chemical reaction.
    • UV-visible spectrophotometers direct UV or visible light at the sample, measuring the absorbance spectrum.

    Stationary Phases

    • TLC, column chromatography, GLC, and HPLC can use various stationary phases with different surface properties.
      • Normal polarity
      • Reverse polarity
      • Ion exchange
      • Size exclusion

    Stationary Phases (Normal Polarity)

    • Silica or alumina stationary phases attract polar molecules via polar groups.
    • Components separate in increasing order of polarity.

    Stationary Phases (Reverse Polarity)

    • Polar sites in silica/alumina are capped with non-polar groups, so non-polar molecules interact strongly.
    • Separation is in decreasing order of polarity.

    Stationary Phases (Cation Exchange)

    • Silica is modified with anionic residues.
    • Cationic species bind with the support and are released using an acid.
    • Separation is according to increasing cationic charge.

    Stationary Phases (Anion Exchange)

    • Silica has cationic residues, attracting anionic species.
    • Separation is according to degrees of anionic charges.

    Stationary Phases (Size Exclusion)

    • Gel beads with set pore sizes separate based on molecular size.
    • Large molecules elute fast, while small molecules have longer paths and elute more slowly.

    A Source of Error (AAS)

    • Another species might absorb at the same wavelength, causing inaccurate results.

    Qualitative Analysis in UV-Visible Spectroscopy

    • Determining absorbed radiation over a range of wavelengths and graphing absorbance or transmittance versus wavelength provides qualitative data and a spectrum.

    Quantitative Analysis in UV-Visible Spectroscopy

    • Compare the absorption of a sample with a calibration graph prepared by measuring the absorption of standard solutions at a particular wavelength.
    • Measure the unknown absorbance and look up the concentration on the calibration graph

    What can be analyzed?

    • UV-Visible spectroscopy is used to measure many types of colored substances.
    • In quantitative analysis, species in solutions are detected, including iodine, organic compounds; as well as metal ions that are naturally colored or that can be chemically converted into colored compounds.

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    Description

    Test your knowledge on the principles of colorimetry and chromatography. This quiz covers topics such as color measurement, the functioning of colorimeters, and various chromatography techniques including high-performance liquid chromatography. Challenge yourself with questions about solvent interactions and stationary phases.

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