Chapter 2 Properties of Matter

1. Chapter 2Properties of Matter Chemistry 1

2. Pure Substances • Matter that always has exactly the same composition • Every sample the same b/c substance has a fixed, uniform composition • 2 categories • Element – Ex: Iron (Fe), Copper (Cu), Gold (Au) 2. Compound – Ex: Water, Sugar, Table Salt

3. Elements • Substance that can’t be broken down into a simpler substance • Only contains 1 type of atom so has a fixed compositon • Atom – smallest particle of an element • Room temp (68oF) = most elements are solid • Elements: • 1 or 2 letters (1st capitalized, 2nd lowercase) • Based on Latin names

4. Compounds • Substance made of 2 or more elements in a fixed proportion • Can be broken down into simpler substances • Compound properties different than elements’ properties that make up compound

5. Mixtures • A mixtureis a blend of two or more kinds of matter, each of which retains its own identity and properties. • mixed together physically • can usually be separated • *Homogeneous mixtures are called solutions • uniform in composition (salt-water solution) • * Heterogeneous mixtures • * not uniform throughout (clay-water mixture)

6. Chapter 1 Classification of Matter

7. Homogeneous vs. Heterogeneous • Not always easy to tell the difference • Observe the properties of a mixture • Size of the particles in mixture effect the properties • Based on the size of its larges particles: solution, suspension, or colloid Solution – homogenous mixture • Liquids do not separate into layers over time • If poured thru a filter, substances are not trapped • Can see thru b/c light passes without being scattered in all directions • Very Small particles

8. Suspensions – heterogeneous mixture • “shake well before use” • Separate into layers • Trapped by a filter • Can scatter light in all directions = cloudy • Large particles • Colloid • Contains intermediate particles • Do not separate into layers • Cannot use a filter to separate • Examples: milk and fog *Scattering of light is a property that can be used to distinguish colloids and suspensions from solutions

9. https://www.youtube.com/watch?v=Vt7lN4QPU0k

10. Physical Properties 2.2

11. Physical Properties • Characteristic of a material that can be observed or measured without changing composition • Viscosity, conductivity, malleability, hardness, melting point, boiling point, density • Viscosity • its resistance to flow • The higher the viscosity, the slower the substance flows • Usually decreases when heated • Conductivity • Ability for heat flow • High conductivity = good conductor  metals • If good conductor of heat, normally good conductor of electricity

12. Physical Properties Cont…. • Malleability • Ability of a solid to be hammered without shattering • Most metals are malleable • Solids that shatter = brittle • Hardness • See what materials scratch the other • Diamond = hardness known material • What do you use to sharpen a knife? • Melting/Boiling Point • Melting Point – Substance changes from a solid to a liquid • Water = 0oC • Wax has low melting point • Boiling Point – Substance boils • Water = 100oC

13. Density • Can be used to test purity • Test purity of methanol (fuel) • d = m/v

14. Using Physical Properties 2.2 • Identifying Material • Decide which properties to test • Run tests on sample of unknown • Compare with previous data reported • Choose Materials • Wouldn’t want a shoelace from wood (must be flexible and durable)

15. Using Properties to Separate Mixtures • Filtration – process that separates materials based on the size of their particles • Small particles can pass thru a strainer • Ex: brewing coffee • Distillation – process that separates the substance in a solution based (liquid)on their boiling points • Ex: fresh water for a submarine • Subs can only hold water for about 10 day  convert seawater to fresh water

16. Recognizing Physical Changes • Occurs when some of the properties of a material change but the substance remains the same • Ex: phase changes • Cutting • Crumpling • Some can be reversed, some can not

17. https://www.youtube.com/watch?v=U5lwgmYr36U

18. Chemical Properties 2.3

19. Observing Chemical Properties 2.3 • Ability to produce a change in the composition of matter • Can only be observed when sample is changing to a different substance • Ex: Candles Burning • Candle = made of paraffin = made of C & H • When candle burns, C combines with air to from Carbon Dioxide and H combines with the air to form water.

20. Chemical Properties • Flammability • Materials ability to burn in the presence of oxygen • Ex: paper and gasoline • Reactivity • How readily a substance combines chemically with other substance • Ex: N – extremely low reactivity • Ex: O – highly reactive element (rust iron & Oxygen)

21. Recognizing Chemical Changes • Substance reacts and forms one or more new substances • Change in Color • Jewelry darkens • Matches turn black • Rust • Production of Gas • Mix vinegar with baking soda = bubbles of carbon dioxide • Baking powder + acid in a cake recipe = bubbles of carbon dioxide • Formation of a Precipitate • Formation of any solid that separates from a liquid mixture • Curdling of milk (lemon juice & milk)

22. Is a Change Chemical or Physical? • Can not be POSITIVE a chemical change has occurred when you see bubbles, color change, or precipitate • Ex: water boiling = physical change • Iron heated = gray  red = physical change • Ask: are different substances present after the change? • Chemical Change = Composition of matter changes • Physical Change = Composition of matter is the same

23. Physical vs. Chemical chemical physical chemical physical physical • Examples: • rusting iron • dissolving in water • burning a log • melting ice • grinding spices

24. https://www.youtube.com/watch?v=37pir0ej_SE