Briefly describe the basic chromatographic process. Be sure to explain how motion is important to the process.
A beam of radiation is passed through a tube containing an unknown sample dissolved in a solution. A detector then compares the intensity of radiation passing through the solution to the intensity of a similar beam of radiation the does not pass through the solution. A signal is fed and produces an absorption spectrum that characterizes the sample being tested.
Briefly describe the basic process of spectrophotometry.
A beam of radiation is passed through a tube containing an unknown sample dissolved in a solution. A detector then compares the intensity of radiation passing through the solution to the intensity of a similar beam of radiation the does not pass through the solution. A signal is fed and produces an absorption spectrum that characterizes the sample being tested.
Define sublimation. What happens to the attractive forces between molecules of a substance that undergo sublimation?
Sublimation is a physical change from the solid state directly into the gaseous state. It causes the forces between molecules to decrease.
Define the terms element and compound and name the smallest unit of each.
An element is the fundamental particle of matter. A compound is a pure substance composed of two or more elements. The smallest unit of an element is an atom. The smallest unit of a compound is a molecule.
Describe the difference between quantitative and qualitative determination.
Qualitative identifies the material in question. Quantitative is the percentage combination of the components of a mixture.
In what area does mass spectrometry currently have its greatest application for forensic scientists?
Mass spectrometry finds its widest application in areas relating to the identification of drugs.
Name the three forms, or states, of matter and explain how the shape and volume of matter are expressed in each state
Three states of matter are solid, liquid, and gas. A solid has both shape and volume. A liquid occupies a specific volume, but takes shape of its container. A gas doesn't have definite volume or shape
What are the main strengths and main weaknesses of ultraviolet spectrophotometry?
The main strength is that the spectra's that are produced are very simple. The weakness is that the spectra of different substances are similar, so the technique may not provide a definite result.
What basic tool is most often used to characterize and identify organic materials? Why is the tool chosen for that purpose?
Spectrophotometry is an analytical method for identifying a substance by its selective absorption of different wavelengths of light. It is the basic tool for the characterization and identification of organic materials.
What is a phase and how can two different phases be distinguished from one another?
A phase is a uniform body of matter, different phases are separated by definite visible boundaries. Different phases can be distinguished from one another by visible boundaries.
What is Beer's law and what analytical technique is based on it?
Beer's law states that the quantity of light absorbed at any frequency is directly proportional to the concentration of material absorbing it. Beer's law permits spectrophotometry to be used as a technique for quantification.
What is color? What determines the color of an opaque object?
Color is a visible indication that objects absorb certain portions of visible light and transmits or reflects others. The colors of opaque objects are determined by which component, color, or colors of light it reflects.
What is electrophoresis and what is it most widely used for?
Electrophoresis is a technique for supporting molecules through the migration on a support medium while under the influence of an electrical potential. In forensic science, electrophoresis finds its most successful application in the characterization of proteins and DNA in dry blood
What is the fundamental difference between organic and inorganic substances?
The difference between organic and inorganic substances is organic is composed of carbon. Inorganic isn't based on carbon.
What is the greatest drawback to spectrophotometry? What technique is often employed when spectrophotometry cannot be used?
Because of the purity of physical evidence is almost always beyond the control of the criminalist this criterion is often not met. For this reason the analytical technique of chromatography is widely applied for the analysis of physical evidence
What is the most important drawback to gas chromatography?
The most important drawback is that a forensic chemist cannot identify an unknown substance based solely on the results of gas chromatography.
What major advantage does infrared spectrophotometry enjoy over ultraviolet spectrophotometry?
The IR spectrum for each substance is unique, because different materials always have distinctively different infrared spectra.
What physical change occurs when a substance undergoes the following changes of state: (a) from liquid to solid, and (b) from liquid to gas?
Substances can change from one state to another. When a substance changes from liquid to solid the forces between the molecules increase strength. When it changes from liquid to gas the attractive forces between the molecules decreases in strength.
What three chromatographic processes are most applicable for solving analytical problems typically encountered in the crime laboratory? What is the main advantage of each?
Gas chromatography, high-performance liquid chromatography, and thin-layer chromatography. Can resolve a highly complex mixture into its components, takes place at room temperature, and is inexpensive.
What two models do scientists use to explain the nature of light? Under what conditions does each model best describe the behavior of light?
The first model describes light as a continuous wave. The second depicts it as a stream of discrete energy particles. Together these two very different descriptions explain all of the observed properties of light.