More About Matter Physical vs. Chemical Properties Physical Properties Observed without changing identity of substance. Ex: color, hardness, density, odor, malleability, ductility, MP temp. Chemical Properties Observed during chemical changes Ex: flammable, explosive, corrosive, rusts, decomposes Chemical vs. Physical Changes Physical Change Does not alter chemical composition. Substance still has same chemical formula. Ex: bend, cut, grind, dissolve, undergo a phase change Chemical Change Chemical composition changes as a reaction occurs. New products formed. Ex: cook food, sour milk, burn wood, explode dynamite What Type of Change? What Type of Change? H2O(s) → H2O(l) 2H2O (l) → 2H2(g) + O2(g) NaCl(s) → NaCl(aq) CH4(g) + O2(g) → CO2(g) + H2O(g) Is it Chemical or Physical? Sometimes it is possible to determine a chemical change using the naked eye. Things to look for: Gas bubbles produced, unusual color change, new odor produced, precipitate forms Precipitate: an insoluble solid that forms when two solutions are mixed. Types of Matter Pure Substance vs. Mixtures Pure Substances Elements • Made up of atoms of one specific type • Have specific physical and chemical properties. • Cannot be broken down by chemical reactions • Ex: Fe, K, Na, Si Compounds Two or more different elements chemically bonded together. Have different chemical and physical properties than elements that make them up. Definite fixed proportions by mass. • Ex: C6H12O6, MgCl2, CO2, NaCl Mixtures Mixtures Two or more pure substances physically combined. Mixtures can be solid, liquid or gaseous. Composition Not Fixed Composition of a mixture is NOT FIXED. Can vary depending on how much of each component is added. Retaining Their Properties Substances in mixtures retain their own properties. Ex: Iron filings (Fe) and sand (SiO2) Even if mixed the iron retains its magnetic properties Clips Mixtures vs. Pure Substances https://www.youtube.com/watch?v=88MBCyi aPSM Types of Mixtures Homogeneous Mixtures Components are distributed uniformly at the molecular level. All true solutions are homogeneous. Aqueous = (aq) dissolved in water or “in solution” If you see (aq) it is a homogeneous mixture Ex: NaCl (aq) Heterogeneous Mixtures Components are not uniformly distributed at the molecular level. Colloids and suspensions are included in this category. How to Tell if a True Solution Tyndall Effect Suspensions and colloids have larger particles that will scatter a beam of light. In a true solution the light will not be scattered Techniques to Separate Mixtures Separating Mixtures Components retain their own properties, so use these properties to separate them. Ex: density, particle size differences, solubility differences, BP temperature, magnetic properties Filtration Ex: Separate water & sand Can be used to separate heterogeneous mixtures Technique cannot be used to separate components of solutions Separatory Funnel Ex: Separate oil and water What type of mixture? Evaporation Ex: Separate sugar from water What type of mixture? Chromatography Solvent runs up paper and components separate out along length of paper depending on level of attraction to solvent. Ex: Separate different types of chlorophyll Distillation Separates two or more liquids, due to differences in boiling point temp. Ex: Separate alcohol and water What type of mixture? Clips Separating Mixtures http://youtu.be/fJXBlfwB_Nw Distillation http://youtu.be/tcJXGIJA9Wo Density Calculating Density Because all matter has mass and volume, all matter has density. No matter the size of the sample, the density doesn’t change. It is a physical property. See Reference Table S for the density of elements. D = M V https://www.youtube.com/watch?v=GnBQ6vIutDM Density of Water Density of Pure Water = 1.0 g/ml If a substance has a density greater than water it will sink, if not it will float. When you dissolve a substance in water it makes it more dense. http://youtu.be/7xGo-HPGKmY Measuring Density (D = M/V) Mass Measured on a scale, often you need to use a weighing dish or a beaker. Volume Can be measured in different ways. For solids the method of water displacement is often used. Density column http://youtu.be/-CDkJuo_LYs Coke vs Diet coke http://youtu.be/5HCmRCGv37s Cool Clips Chemical Reactions (Bill Nye) http://youtu.be/1MiVyBHQmJk http://youtu.be/66kuhJkQCVM Steve Spangler (clock reactions) http://youtu.be/BqeWpywDuiY Diet Coke and Mentos http://youtu.be/9vk4_2xboOE