Physical and Chemical Properties More About Matter Physical and Chemical Properties

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 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.

Pure Substance vs. Mixtures Types of Matter Pure Substance vs. Mixtures

Elements (Pure Substance) 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 (Pure Substance) 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 The numbers written below the symbols are called “subscripts” and let us know about the number of each type of atom in the compound

Mixtures Two or more pure substances physically combined. Mixtures can be solid, liquid or gaseous.

Mixture’s Composition is Not Fixed Can vary depending on how much of each component is added. Ex: One teaspoon of sugar in water or ten teaspoons it’s still a sugar water mixture.

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 https://www.youtube.com/watch?v=88MBCyiaPSM

Element, Compound or Mixture?

Types of Mixtures

Homogeneous Mixtures Components are distributed uniformly at the molecular level. All true solutions are homogeneous.

If you see (aq) it is a homogeneous mixture Aqueous = (aq) dissolved in water or “in solution” Ex: NaCl (aq)

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

Heterogeneous Mixtures Components are not uniformly distributed at the molecular level. Colloids and suspensions are included in this category.

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 Separates components with different particle sizes. Use various types of filter paper

Separatory Funnel Ex: Separate oil and water What type of mixture? Used to separate out two liquids that do not mix together.

Evaporation Ex: Separate sugar from water What type of mixture? Separate out a liquid from a dissolved solid. Use evaporating dishes or watch-glass Liquid is allowed to evaporate off and solid crystals are left behind

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? Each liquid reaches its B.P., becomes a gas and then is recondensed in its pure state.

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 can change under different pressure and temperature conditions. This is especially true for gases which can expand and contract in volume easily.

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

Clips Separating Mixtures http://youtu.be/fJXBlfwB_Nw Distillation http://youtu.be/tcJXGIJA9Wo

Cool Clips Showing Chemical Change 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