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 (B)

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

Ethanol concentration can be determined using a calibration graph.

<p>True (A)</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 (B)</p> Signup and view all the answers

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

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

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

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

All light waves travel at different speeds in a vacuum.

<p>False (B)</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 (A)</p> Signup and view all the answers

Emission spectra are characterized by continuous energy emission.

<p>False (B)</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 (C)</p> Signup and view all the answers

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

<p>False (B)</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 (C)</p> Signup and view all the answers

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

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

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

<p>False (B)</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 (A)</p> Signup and view all the answers

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

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

Flashcards

Ethanol Concentration Determination Using Standards

A technique used to measure the concentration of ethanol in a sample by comparing the area under the peak of the unknown sample to a series of known standards.

Calibration Graph

A graph showing the relationship between the concentration of ethanol and the area under its peak in a chromatogram.

High Performance Liquid Chromatography (HPLC)

A type of chromatography that uses a high pressure to separate a mixture of components based on their differences in polarity or size.

Stationary Phase

The solid material packed inside the chromatography column that interacts with the components of the mixture being separated.

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Normal Polarity Stationary Phase

A type of stationary phase where the surface is polar and attracts polar molecules, leading to separation based on polarity.

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Reverse Polarity Stationary Phase

A type of stationary phase where the surface is non-polar, attracting non-polar molecules and leading to separation based on polarity.

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Ion Exchange Stationary Phase

A type of stationary phase that interacts with charged molecules based on their charge.

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Size Exclusion Stationary Phase

A type of stationary phase that separates molecules based on their size, allowing smaller molecules to pass through more easily.

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Cation Exchange Chromatography

A stationary phase where silica is modified with anionic groups, enabling strong interactions with positively charged species (cations). Cations are then eluted from the stationary phase using an acid (H+).

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Anion Exchange Chromatography

A stationary phase where silica is modified with cationic groups, enabling strong interactions with negatively charged species (anions). Anions are then eluted from the stationary phase using an acid (H+).

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Size Exclusion Chromatography

A stationary phase where separation is based on molecular size, meaning larger molecules elute first and smaller molecules elute last. It's like a sieve where bigger particles pass through more readily.

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Elution

The process of molecules moving through a chromatography column and exiting it.

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Continuous Spectrum

A spectrum that shows a continuous range of wavelengths of light emitted by a heated object.

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Line Spectrum

A spectrum that shows a series of discrete lines representing specific wavelengths of light emitted by excited atoms.

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Absorption

The process of atoms absorbing electromagnetic radiation, causing electrons to move to higher energy levels.

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Emission

The process of atoms emitting electromagnetic radiation as excited electrons return to lower energy levels.

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Absorption Spectrum

A spectrum that shows the wavelengths of light that are absorbed by a sample, revealing the presence of specific substances.

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Beer-Lambert Law

The principle that the amount of light absorbed by a substance is directly proportional to its concentration.

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Colorimetry

A quantitative technique that measures the intensity of a colored solution's color, directly correlating it to the concentration of the colored substance within it.

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Colourimeter

A device used in colorimetry to analyze the absorbance of light by a colored solution, providing a more precise determination of the concentration of the colored substance.

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Absorbance

The amount of light absorbed by a solution, which is directly related to the concentration of the colored substance.

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Cuvet

A small container used in colorimetry to hold the solution being analyzed and ensure the path length of the light beam is consistent.

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Zero Adjustment

The process of adjusting a colourimeter to eliminate interference from the surrounding solution and the cuvet itself, ensuring accurate absorbance measurements.

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What is UV-Vis spectrophotometry?

UV-Vis spectrophotometry involves measuring the amount of light absorbed by a sample at specific wavelengths in the ultraviolet (UV) and visible (Vis) regions of the electromagnetic spectrum.

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What is the role of the light source in a UV-Vis spectrophotometer?

The UV-Vis spectrophotometer uses a light source that can emit both visible and ultraviolet light. The specific type of light emitted depends on the experiment.

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What is UV-Vis spectroscopy?

The process of measuring absorbance (amount of light absorbed) and plotting it against wavelength.

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Why do carrots appear orange?

Carotene, the pigment in carrots, absorbs blue light strongly, which means it reflects orange and red light, making the carrot appear orange.

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What is the purpose of a solvent blank in UV-Vis spectrophotometry?

Before measuring the sample's absorbance, the instrument is calibrated by using a solvent blank. This ensures that any measured absorbance is solely due to the analyte.

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Atomic Absorption Spectroscopy (AAS)

A technique used in analytical chemistry to determine the concentration of a specific element in a sample by measuring the absorption of light by atoms of that element.

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Hollow Cathode Lamp

A specialized type of light source used in atomic absorption spectroscopy (AAS) to generate specific wavelengths of light that are absorbed by the target element.

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Atomization

The process in AAS where the sample is heated to a high temperature, converting the analyte into free atoms in the gaseous state.

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Absorption Wavelengths

The wavelengths of light that are absorbed by a specific element's atoms. These wavelengths are unique to each element and can be used for identification.

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Sensitivity

In AAS, this refers to the ability of the instrument to detect very small concentrations of the target element.

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Flame Adjustment

The process of adjusting the conditions of the flame in atomic absorption spectroscopy (AAS) to ensure optimal atomization and light absorption by the analyte.

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Interference

This refers to any element other than the analyte that may also absorb light at the same wavelength, potentially leading to inaccurate readings.

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Specificity

The ability of AAS to measure the concentration of only the target element, minimizing interference from other components in the sample.

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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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