in Crime Scene Investigation T. Trimpe Using

A Few Basics... Mixture – Two or more substances that are mixed together, but not chemically combined. Examples of mixtures... Air – mixture of gases – separate oxygen from nitrogen Bowl of cereal – mixture of cereal and milk – separate pieces of cereal from the milk Soda pop – mixture of soda syrup, water, and CO 2 gas Fog – water suspended in air – does it always stay foggy? How does the water separate from the air? Kool-Aid – mixture of water, sugar, and flavor crystals Examples of compounds... Salt –Sodium and chlorine combined chemically – NaCl Water –Hydrogen and oxygen combined chemically – H 2 0 Carbon Dioxide – Carbon and oxygen combined chemically – CO 2 Compounds – Two or more elements that are chemically combined.

QUICK CHECK Which of these are mixtures? NaCleggsCaO 2 cell phoneKF Which of these are compounds? NaCleggsCaO 2 cell phoneKF How do you know? Talk with one other student about your answers…

Solutions Solutions are mixtures in which one substance is dissolved in another. Solutions have two parts: SOLUTE and SOLVENT! The solute is the substance that is dissolved. The solvent is the substance that does the dissolving Identify the solute and solvent in each solution... (answer on your sheet) SolutionSoluteSolvent Lemonade Kool-Aid Ocean water Solubility - A measure of how much of a substance will dissolve in a liquid. * A substance that does dissolve in the solvent is called soluble. * A substance that does not dissolve in the solvent is called insoluble.

QUICK CHECK Which one is the solvent? The water is dissolving the salt! Which one is the solute? The sugar is being dissolved by the water! How do you know? Talk with one other student about your answers…

What is Chromato graph y? From Wikipedia... Chromatography (from Greek word for chroma = color and graphein = write) lab technique to separate (break apart, divide) mixtures (something that can be separated)… Which means... Chromatography is the physical separation of a mixture into its individual components. We can use chromatography to separate the components of inks and dyes, such as those found in pens, markers, clothing, and even candy shells. Chromatography can also be used to separate the colored pigments in plants.

QUICK CHECK Why do we use chroma to graph y? Talk with one other student about your answers…

Types of Chromatography Gas Chromatography is used in airports to detect bombs and is used is forensics in many different ways. It is used to analyze fibers on a persons body and also analyze blood found at a crime scene. Helium gas is used to move a gaseous mixture through a column of absorbent material. Liquid Chromatography is used in the world to test water samples to look for pollution in lakes and rivers. It is used to analyze metal ions and organic compounds in solutions. Liquid chromatography uses liquids which may have solids (insoluble molecules). Thin-layer Chromatography uses an absorbent material on flat glass or plastic plates. It is used to detect pesticide or insecticide residues in food. Thin-layer chromatography is also used in forensics to analyze the dye composition of fibers. Paper Chromatography is one of the most common types of chromatography. It uses a strip of paper and capillary action is used to pull the solvents up through the paper to separate the solutes.

Quick Overview… Paper Chromatography: You will use water as a solvent to spread out the solute’s identities. You will test different markers and pens to see what they are made up of using “chromatography” Using strips of paper, you will dip the edge of the paper into the water for 10 minutes without touching the color to the water. The water will dissolve the ink into different colored bands on the paper – Chromatography!

Paper Chromatography Demo We will be using this method of chromatography during our unit. Watch the short video carefully (close the ad by clicking on the X). VIDEO

QUICK CHECK What type of chroma to graph y will we use in this investigation? What materials will you need?

Why does a CSI Need to Know About Chromatography? Answer this question on your paper … (Why would a CSI need to use this technique?)

Directions Obtain (get) the supplies you’ll need from your teacher. –Beaker with a small amount of water –Paper strips –Pencil –Markers for testing –Masking tape –Timer Cut the strip so that it will be at the correct height – long enough to reach the top level of the water. Write the pen number on the strip using a pencil or permanent marker. Use one of the testing markers to draw one line on the paper strip at about a 1/2 inch from the bottom. You don’t want the ink line to touch the water. Tape the top of the strip to a pencil and hang in the water for 10 minutes. Remove the strip from the water and use a pencil to mark the line between the wet and dry portions of the strip. Allow the strip to dry. Pencil Paper Ink Tape – Label with marker

Answer the questions on your guided notes sheet…follow the directions! Good Luck!