Knowt
forensics pt 1
Qualitative Analysis
Qualitative analysis is the first section of the rules, involving the identification of unknown powders. Competitors may be asked to identify 3-8 samples at the regional level, 6-10 samples at the state level, and 10-14 samples at the national level. All teams will have the same set of solids to identify, but some samples may occur more than once.
Fifteen different substances are included in the rules manual. These are sodium acetate, sodium chloride, sodium hydrogen carbonate, sodium carbonate, lithium chloride, potassium chloride, calcium nitrate, calcium sulfate, calcium carbonate, cornstarch, glucose, sucrose, magnesium sulfate, boric acid, and ammonium chloride. Many of these powders are accessible in local stores or available on Amazon.com.
Methods of Identification
Many competitors utilize a flow chart or table which they use to identify powders. Developing a strategy for how to test the samples can aid with time management and ensure that all the given powders can be identified accurately. Additionally, utilizing all available means of identification will give the best results and help draw a more accurate conclusion.
Solubility
All samples can be divided into two fields--soluble and non-soluble. Water is used to perform this test.
Soluble Samples: sodium acetate, sodium chloride, sodium hydrogen carbonate, sodium carbonate, lithium chloride, potassium chloride, calcium nitrate, glucose, sucrose, magnesium sulfate, boric acid, ammonium chloride
Non-soluble Samples: calcium sulfate, calcium carbonate, cornstarch
A word of caution: every compound has a unique solubility product constant (Ksp), which indicates the amount of compound that can dissolve in a given volume of water before it reaches a point where no more of that compound can dissolve in the solution. This is called saturation. Because of this, it may be possible for a powder to appear to not be dissolving in water if there is too much of it and not enough water. Be careful of this when observing solubility, and, when in doubt, go for using smaller quantities of the sample.
pH
The pH data for chemicals can be useful, especially for determining between two similar chemicals. Most samples have a pH of between 5 and 8, but there are several chemicals that have distinct pHs. For example, sodium carbonate has a pH of 10, and boric acid has a pH of 4.
There are many different kinds of pH paper, sometimes also called litmus paper, that can be used to perform this test. Any kind should do. The test involves dissolving some of the dry powder in water, dipping the end of the pH paper in the solution, and comparing the resulting color to the palette on the package to see which pH value corresponds to it.
Flame test
The flame test uses a Bunsen burner and a nichrome wire. If nichrome wire is not available, wooden splints (such as coffee stirrers) soaked in water work and dry samples of the powder on the tip of a spatula or scoopula work well too. To perform this test, dip a clean nichrome wire in distilled water, and then dip the loop of the wire into a small sample of the dry chemical. Hold the loop of the wire in the cone of the flame and observe the color of the burning chemical. If desired, a piece of cobalt blue glass may be used for viewing. Chemical cations determine the color of the flame, and their characteristics may indicate the chemical identity.
Sodium: golden yellow flame, very distinct. Even a small amount of sodium will contaminate other compounds.
Lithium: carmine or red flame
Calcium: yellow-red flame
Boric Acid: bright green flame, very visible
Ammonium Chloride: faint green flame
Potassium: light purple, lavender flame
Note that sodium can easily contaminate some substances, and its presence can mask the other cation colors, giving off a yellow flame. The purpose of the cobalt blue glass is to block off the yellow color given by sodium in case the sample may have been contaminated. In some cases, this yellow color can appear a little golden or orangish, rather than a lemon-like tint of yellow. Some powders have been said to not give off a flame color, including, but not limited to, calcium sulfate and calcium carbonate, which will be evident. Cleaning nichrome wires should help, though that is not guaranteed. To do this, stick the wire into the flame until no color is observed (or until the wire glows orange, whichever happens first). Next, dip the wire into acid (hydrochloric acid should do the trick, as it should be readily available during the competition for obvious reasons). Finally, dip it into deionized water, and then it's ready for use again. This problem can perhaps also be solved by just bringing an abundance of utensils to decrease the chances of needing to clean any, but this method of cleaning nichrome wires should help in the case having more tools is not a viable option.
There are additional properties of some of the powders that can also be observed in a flame test. For example, heating a carbohydrate such as glucose or sucrose will cause it to melt and caramelize. Heating dry ammonium chloride for a few seconds will cause it to release white wisps of smoke. These are best observed with the method of putting dry powder on the tip of a spatula or a scoopula and holding it directly in the flame.
Tests with liquid reagents
Liquids used for identification are iodine, sodium hydroxide, and hydrochloric acid. These reagents will be provided by the event supervisor.
Iodine: When iodine is added to cornstarch, the sample will turn black. If cornstarch is not present, the iodine will remain brown.
Sodium Hydroxide: Sodium hydroxide is used simply to categorize your samples into two fields: NaOH reactive- and non-reactive. For this reason, it is extremely useful when using a flowchart. To perform this test, a few drops of NaOH are added to a small sample of chemical dissolved in water. If a milky-white precipitate forms, the sample is NaOH reactive. If a precipitate does not form, the sample is NaOH non-reactive.
Hydrochloric Acid: Hydrochloric acid will react when added to samples containing carbonates--therefore, it is useful in identifying calcium carbonate, sodium carbonate, and sodium hydrogen carbonate.
Benedict's solution
Benedict's solution is used to detect reducing sugars such as glucose. To perform this test, dissolve a small sample of chemical in water in a test tube. Add two to three drops of Benedict's solution, then place the test tube in a hot water bath. If the glucose is present, the sample will react and form an orange precipitate. This test may take a few minutes; be patient. An important fact to note is that sucrose will not react with Benedict's solution but glucose will. Benedict's solution can also be used to test for ammonium chloride. Adding a couple of drops will turn the sample a dark blue.
Conductivity
Certain chemical samples will dissociate and become conductive when dissolved in water. To perform this test, dissolve a small sample of dry chemical in water. Using a 9-volt conductivity tester will determine whether a sample is conductive or semi-conductive. This data is especially helpful when following a flowchart, and is the most useful for identifying ionic compounds.
Polymers
A polymer is a chain-like molecule made up of individual repeating subunits called monomers. These chains can be linear or branched, resulting in many possible polymers with different structures. Heteropolymers/copolymers are polymers made up of multiple different subunits, while homopolymers consist of one repeating subunit. Polymers can also be formed in a variety of different ways, though the two most relevant to this event are condensation and addition. When a polymer is formed by condensation it will produce a small molecule like water as a byproduct. However, polymerization by addition will not form a byproduct. Addition polymers can be more difficult to recycle as they form stronger bonds between each monomer unit. Comparatively, it is easier to break down a polymer made by condensation (which makes them more biodegradable).
There are three types of polymers in the forensics rules: plastics, fibers, and hairs. The main methods of identifying these polymers will be discussed in each section, but the three main techniques are burn tests, density tests, and examination under the microscope. Burn tests are permitted on fibers and hairs but not plastics, since burning plastic can be a hazard. However, a test writer may still provide a written description of how the plastic behaves when it burns.
