1 Matter: Properties and Changes

2 Physical Properties can be observed without changing the identity of the substance. Ex… ~ color~ conductivity ~ taste~ viscosity ~ odor ~ elasticity ~ size ~ hardness ~ shape ~ magnetism ~ texture ~ boiling/ melting point melting point and many more…

3 But one of the most useful is Density: the amount of matter present in a given volume. ~ or how heavy a substance is compared to how much space it takes up Ice is less dense than water; it floats on water A is more dense than B (there is more matter and less space); B and C are of similar densities b/c the ratios of matter and space are about the same

4 Calculating Density Units: m = g v = mL or cm 3 D = g/ml or g/cm 3 Density = mass / volume D = m/v D = m/v m = Dv m = Dv v = m/D v = m/D

5 Density Problems 1. A nail has a vol. of cm 3 and a mass of grams. What is the density of the nail? D = m/v D = m/v D = g ÷ cm 3 D = g ÷ cm 3 D = 7.86 g/cm 3 D = 7.86 g/cm 3 2. Vegetable oil has a density of g/ml. Calculate the mass of ml of oil. m = D × v m = D × v m = g/ml × ml m = g/ml × ml m = 458 grams m = 458 grams 3. The density of a piece of wood is 0.86 g/cm 3. What is the volume of the wood if its mass is 75 grams? v = m/D v = m/D v = 75 g ÷ 0.86 g/cm 3 v = 75 g ÷ 0.86 g/cm 3 v = 87 cm 3 v = 87 cm 3

6 Measuring Density To measure the density of an object… 1. find the mass of the object using a balance 2. find the volume of the object: a) for regular solids – use a ruler, l x w x h b) for irregular solids - use the water displacement method (unless solid dissolves or floats) c) for liquids – use a graduated cylinder c) for liquids – use a graduated cylinder

7 Buoyancy - Density and buoyancy are physical properties - Buoyancy is the force with which a more dense fluid pushes a less dense substance upward

8 Which of the following statements explains why a steel ship will float on water but a bar of steel will sink. a.When rolled into a sheet, steel is less dense than water. b.The densest part of the ship is the part that is out of the water. c.Because of the shape and the air in the hull, the overall density of the ship is less than the density of water. A boat floats because….

9 Physical Changes are changes in appearance only… NOT in chemical make-up Includes… ~ dissolving ~ changes in shape ~ changes in size ~ changes in phase

10 Examples of physical changes... ~ breaking a window ~ tearing / cutting a piece of paper ~ melting a piece of ice ~ melting a piece of ice ~ dissolving sugar in hot tea ~ painting wood ~ shaping metal

11 Chemical Properties properties that explain HOW a substance will react or behave. The substance must be changed into something new to observe the property. Ex: ~ reactivity to… water water acids acids bases bases ~ flammability ~ ability to lose electrons ( be oxidized)

12 Chemical Changes Are changes that result in a recombination of atoms – the formation of NEW substance(s)! Evidence that a chemical change has occurred: Evidence that a chemical change has occurred: ~ gas / bubbles given off ~ formation of precipitate (solid) ~ heat given off / absorbed (breaking/making chem. bonds) ~ light given off ~ color change (if new substance) ~ you can’t get the original substance back without a chemical reaction.

13 Examples of chemical changes: ~ silver tarnishing ~ a nail rusting ~ burning a match ~ food rotting or souring or souring ~ baking bread Striking a match releases heat and light and results in ash, smoke and gas Cooking bread changes the color, texture, odor, taste