Determination of an Unknown Chemical Substance Rachel Zammit

One type of investigation that a chemist performs is chemical analysis One type of investigation that a chemist performs is chemical analysis. The goal of chemical analysis is to answer the questions: "What is this sample composed of, and how much of each constituent is present?" The analysis can be qualitative or quantitative.

Qualitative analysis The result of the analysis is a list of ingredients ("this sample contains chemicals X and Y") Quantitative analysis The result is a list of ingredients and the concentration of each ingredient ("this sample contains 3.2 percent of chemical X and 96.8 percent of chemical Y”)

If a chemist is asked to determine if a sample of soil has mercury in it, at any level, is that a qualitative or a quantitative question? Question

Forensic scientists often need to identify unknown powders that may be illegal drugs. There are two categories of forensic tests used to analyse drugs and other unknown substances: Presumptive tests (such as colour tests) give only an indication of which type of substance is present but they can't specifically identify the substance. Confirmatory tests (such as chromatography/mass spectrometry) are more specific and can determine the precise identity of the substance.

Techniques used to identify an unknown substance Physical Properties Appearance Colour Melting Point Chemical Properties Solubility in water Chemicals it reacts with Techniques used to identify an unknown substance

Techniques used to identify an unknown substance Colour Test Expose an unknown drug to a chemical or mixture of chemicals. What colour the test substance turns can help determine the type of substance that's present. Techniques used to identify an unknown substance

Techniques used to identify an unknown substance Chromatography Thin-layer chromatography incorporates a solid stationary phase and a moving liquid phase to cause a separation of the constituents of a mixture. The distance a component has travelled up a plate can be assigned a numerical value known as the Rf value. Rf = Distance travelled by the component Distance travelled by the solvent Techniques used to identify an unknown substance

Determine the Rf values for the following substances

Techniques used to identify an unknown substance Ultraviolet spectrophotometry Analyses the way the substance reacts to ultraviolet (UV) and infrared (IR) light. A spectrophotometry machine emits UV and IR rays, and then measures how the sample reflects or absorbs these rays to give a general idea of what type of substance is present. Techniques used to identify an unknown substance

It is possible that a forensic scientist might find a white powder at the scene of a crime. Without testing the substance, the scientist cannot know if the substance was legal or illegal. Many commonly found white powders have been previously tested so that the results of the tests can be compared to the test results of the powder taken from the crime scene. This allows the scientist to rule out legal substances. Setting the Scene

Can you identify these substances?

Salt Corn Starch Sugar

A police officer makes a routine traffic stop in an area where there has been illegal drug activity. The officer notices white powder on the seat of the car and requests a sample to be taken. The powder might just be where the driver had groceries and a container of sugar opened and spilled… Or the powder might be an illegal substance. Scenario 1

Several kids have become sick after eating at the school cafeteria, each complaining about stomach ache and nausea. After questioning the students, it became clear that they all had one dish in common – the chilli. Upon further investigation, it turns out that a bottle containing aspirin in the form of crystals is missing from a chemistry classroom. Did the aspirin somehow end up in the chilli? Scenario 2

An elderly woman is rushed to the hospital complaining of severe abdominal pain. The doctor learns that the woman takes no medicines except aspirin for her arthritis. Since she cannot swallow pills well she takes a powdered form of aspirin which she buys in bulk and keeps in a plastic container in her kitchen next to her baking goods. She had just finished a day of baking sweets and admits she samples while she bakes and thought that she had just had too many sweets. Immediately the doctor suspects that she has mixed up the aspirin and another ingredient and is suffering from aspirin poisoning. The doctor quickly pumps her stomach. Soon the woman is feeling well again, but the doctor needs to confirm the diagnosis before releasing her. If the doctor is wrong, the woman could be suffering from something far more severe. If the doctor is right, the poisoning could easily occur again unless the aspirin is located and properly labelled Scenario 3

http://chemistry. about http://chemistry.about.com/od/growingcrystals/ig/Crys tal-Photo-Gallery/Sugar-Crystals---Sucrose.htm http://biozz.deviantart.com/art/Table-Salt-179603487 http://www.starwest-botanicals.com/product/1- cornstarch-powder.html http://www.sciencebuddies.org/science-fair- projects/project_ideas/Chem_p093.shtml#summary http://resources.mhs.vic.edu.au/science/elective/resou rces/chromatography.htm References