Title: CHE2DEV Env Water Qual Quiz 4

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Q: Select the correct statement.
- An optode is an optical electrode that generates a potentiometric response to a particular analyte.
- Tris(4,7-diphenyl-1,10-phenanthroline)Ruthenium(II) chloride is a luminescent compound that can be used as a sensor reagent for dissolved molecular oxygen.
- Increased levels of dissolved molecular oxygen in a water sample provide an enhanced luminescence response.
- Microbes are added to a water sample to consume dissolved oxygen (DO) to enable a zero calibration.
A: Tris(4,7-diphenyl-1,10-phenanthroline)Ruthenium(II) chloride is a luminescent compound that can be used as a sensor reagent for dissolved molecular oxygen.

Q: Select the correct statement.
- Amalgamated cadmium is used to oxidise nitrite (NO_2^-) to nitrate (NO_3^-) for standard colorimetric analysis.
- Sulfate (SO_4^2-) is not readily detected in aerobic surface waters as it is readily oxidised to sulfide (S^2-).
- Copper and iron salts are added to water samples to enhance the reduction of all nitrate (NO_3^-) to nitrite (NO_2^-) during colorimetric analysis.
- Some bacteria use sulfate as an alternate source of oxygen under anaerobic conditions to release sulfide species during the decomposition of sulfur containing organic matter.
A: Some bacteria use sulfate as an alternate source of oxygen under anaerobic conditions to release sulfide species during the decomposition of sulfur containing organic matter.

Q: Select the correct statement.
- Accurate kinetic studies requiring constant monitoring of the incident and transmited light are best done using a double-beam spectrometer.
- Single-beam spectrometers are best used to simultaneously monitor sample and reference cells.
- A monochromator is used to select the characteristic analytical wavelength of a chromophore prior to detection after passing polychromatic light through the sample.
- Deconvolution of over-lapping spectra cannot be used to determine concentrations of individual chromophores in complex samples.
A: Accurate kinetic studies requiring constant monitoring of the incident and transmited light are best done using a double-beam spectrometer.

Q: Select the correct statement.
- Emission of photons of various energies from a vibrational ground state to excited states is known as luminesence.
- Luminescence measurements are more sensitive than absorption measurements because the resultant photon emission is measured without interference from the initial excitation light source.
- Phosphorescence is rapidly decaying luminescence that is extinguished in the absence of an excitation source.
- Luminescence spectrometers have a simplier optical system for the transmission of light compared to absorption spectrometers.
A: Luminescence measurements are more sensitive than absorption measurements because the resultant photon emission is measured without interference from the initial excitation light source.

Q: Select the correct statement.
- The standard method for copper determination involves chelation of Cu^2+ with neocuproine reagent to produce a strong chromophore that absorbs at 457 nm.
- Although copper is found naturally in environmental waters it is a non-essential element for plant and animal metabolism.
- Corrosion of copper in pipes and heat exchangers is reduced by maintaining a low pH in water supplies.
- Levels of copper greater than 2 mg/L in potable waters do not pose any significant health risks.
A: The standard method for copper determination involves chelation of Cu^2+ with neocuproine reagent to produce a strong chromophore that absorbs at 457 nm.

Q: Select the correct statement.
- The standard colorimetric method for the determination of phenols involves a reaction with 4-aminoantipyrine in the presence of alkali (OH^-) and ferricyanide (Fe(CN)_6^3-) to produce a strong chromophore that absorbs "blue" light
- Purification of water supplies by chlorination does not affect phenol compounds.
- Various substituted phenols can be differentiated and determined individually by the standard colorimetric method for phenols.
- Phenol compounds in anaerobic environmental waters are readily decomposed by microbes.
A: The standard colorimetric method for the determination of phenols involves a reaction with 4-aminoantipyrine in the presence of alkali (OH^-) and ferricyanide (Fe(CN)_6^3-) to produce a strong chromophore that absorbs "blue" light

Q: Select the correct statement.
- Absorption of light by a sample increases the measured incident radiation power.
- Molar absorptivity (or extinction coefficient) of a chemical species at a particular wavelength can be determined by a plot of Absorbance versus Concentration.
- Measured absorbance of a chemical species can be increased by using a cell with a reduced pathlength.
- Absorbance values have units of M^-1.cm^-1.
A: Molar absorptivity (or extinction coefficient) of a chemical species at a particular wavelength can be determined by a plot of Absorbance versus Concentration.

Q: Select the correct statement.
- Orthophosphate anions can be directly measured with good sensitivity.
- Some hydrated metal ions like Cu(H_2O)_6^2+ absorb strongly in the ultraviolet region and can be directly measured.
- Many metal ions are measured with better sensitivity as metal-ligand complexes.
- Phenols can be directly measured with good sensitivity because they contain a "strong" aromatic chromophore.
A: Many metal ions are measured with better sensitivity as metal-ligand complexes.

Q: A chromophore is the part of a molecule that [...] light.

It generally consists of an extended [...] bond system.
Some organic molecules contain [...] ring systems that are strong chromophores.
Other organic molecules need the chemical addition of a strong chromophore species like a [...].
A: absorbs; conjugated; aromatic; dye

Q: Select the correct statement.
- The absorbance of a chromophore can only be measured at a single wavelength.
- UV-Vis Spectroscopy exhibits a large linear useful calibration range from 10^-2 to 1 M.
- Dissociation and polymerisation reactions are a useful means of increasing the measured sensitivity of the analyte
- Problematic changes in the refractive index of a sample solution that cause a non-linear calibration are minimised by only measuring dilute solutions less than 10^-2 M.
A: Problematic changes in the refractive index of a sample solution that cause a non-linear calibration are minimised by only measuring dilute solutions less than 10^-2 M.