Methods of Separating Mixtures Magnet Filter Decant Evaporation Centrifuge Chromatography Distillation Filtration separates a liquid from a solid Mixture of solid and liquid Funnel Filter paper traps solid Stirring rod Filtrate (liquid component of the mixture) Chromatography Tie-dye t-shirt Black pen ink DNA testing Tomb of Unknown Soldiers Crime scene Paternity testing Paper Chromatography Separation by Chromatography sample mixture a chromatographic column stationary phase selectively absorbs components mobile phase sweeps sample down column detector http://antoine.frostburg.edu/chem/senese/101/matter/slides/sld006.htm 1
detector response 9/13/2013 Separation by Chromatography Ion chromatogram of orange juice K + sample mixture a chromatographic column Na + Mg 2+ Fe 3+ Ca 2+ stationary phase selectively absorbs components mobile phase sweeps sample down column detector 0 5 10 15 20 25 time (minutes) http://antoine.frostburg.edu/chem/senese/101/matter/slides/sld006.htm Setup to heat a solution A Hero s Fountain Glass retort Ring stand mixture for distillation placed in here Beaker long spout helps vapors to condense Wire gauze Ring Bunsen burner Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 42 Eyewitness Science Chemistry, Dr. Ann Newmark, DK Publishing, Inc., 1993, pg 13 Furnace A Distillation Apparatus The solution is boiled and steam is driven off. thermometer liquid with a solid dissolved in it condenser tube distilling flask Dorin, Demmin, Gabel, Chemistry The Study of Matter, 3 rd Edition, 1990, page 282 hose connected to cold water faucet receiving flask pure liquid Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 39 2
Salt remains after all water is boiled off. No chemical change occurs when salt water is distilled. Distillation (physical method) Salt Saltwater solution (homogeneous mixture) Pure water Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 39 Separation of a sand-saltwater mixture. Separation of Sand from Salt 1. Gently break up your salt-crusted sand with a plastic spoon. Follow this flowchart to make a complete separation. Saltcrusted Weigh the mixture. Pour into heat-resistant container. Fill with water. Stir and let settle 1 minute. Calculate weight of salt. Weigh Dry Decant clear liquid. No 2. How does this flow chart insure a complete separation? Evaporate to dryness. Yes Repeat 3 times? Wet Centrifugation Water Molecules Spin sample very rapidly: denser materials go to bottom (outside) Separate blood into serum and plasma Serum (clear) Plasma (contains red blood cells RBCs ) Check for anemia (lack of iron) AFTER Before Serum Blood RBC s A B C Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 8 3
The decomposition of two water molecules. Electrolysis Water electro = electricity lysis = to split Oxygen gas forms Hydrogen gas forms Water molecules Diatomic oxygen molecule + Diatomic hydrogen molecules H 2 O(l) *H 1+ O 2 (g) + 2 H 2 (g) Electric current water oxygen hydrogen Source of direct current Electrode 2 H 2 O O 2 + 2 H 2 *Must add acid catalyst to conduct electricity Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 32 Electrolysis of Water D.C. power source anode Half reaction at the cathode (reduction): 4 H 2 O + 4 e - 2 H 2 + 4 OH 1- Half reaction at the anode (oxidation): 2 H 2 O O 2 + 4 H 1+ + 4 e - oxygen gas water hydrogen gas cathode Physical Properties List seven examples of physical properties. Describe three uses of physical properties. Name two processes that are used to separate mixtures. When you describe a liquid as thick, are you saying that it has a high or low viscosity? Physical Properties Explain why sharpening a pencil is an example of a physical change. What allows a mixture to be separated by distillation? Chemical Properties Under what conditions can chemical properties be observed? List three common types of evidence for a chemical change. How do chemical changes differ from physical changes? 4
Chemical Properties Explain why the rusting of an iron bar decreases the strength of the bar. A pat of butter melts and then burns in a hot frying pan. Which of these changes is physical and which is chemical? 5