Pure Substances vs. Mixtures Physical and Chemical Changes

1. What's the "Matter"? Pure Substances vs. Mixtures Physical and Chemical Changes

2. Everything that has mass and takes up space is called matter. What is matter?

4. What are "pure substances"? Matter that has a fixed composition and definite properties. (chemical and physical)

5. There are two kinds of pure substances Elements Compounds

6. Elements • Substance that cannot be separated or broken down into simpler substances by chemical means. • Ex’s- any box on the periodic table • Made of only 1 type of atom • The smallest unit of an element that maintains the properties of that element • HUH?

7. The smallest unit of an element that maintains the properties of that element??? • The element sodium has certain properties • 11 protons, 11 electrons…boiling point, etc

8. Compounds cont… • Substance made of atoms of 2 or more different elements that are CHEMICALLY combined. • Elements are combined in a definite way and this changes their properties Na- lethal if ingested Cl- lethal if ingested NaCl- table salt

9. Molecules • Two or more atoms bonded together… • Ex- O2, NaCl, etc. • Not all molecules are compounds, but all compounds are molecules…explain

10. Compounds Molecules made by two or more elements bonded together -always in a definite ratio Elements Molecules made of just one element What is a pure substance? Na (sodium) NaCl (sodium chloride/salt)

11. Characteristics of Pure Substances • Cannot be separated into simpler substances by physical methods (physical changes) • Fixed composition • Properties do not vary • Can be expressed with a chemical formula • Ex H2O, NaCl, H

13. What is a mixture? • Mixtures are two or more substances that are physically combined. • (NOT chemically combined like a pure substance) • May be separated into pure substances by physical methods

14. Examples of Mixtures

15. Characteristics of Mixtures • Components retain their characteristic properties and can be separated by physical means. • http://videos.howstuffworks.com/hsw/22540-together-but-separate-suspensions-video.htm This sand and iron filings mixture can be separated using a magnet.

16. Two types of mixtures

17. Homogenous Mixtures • Homogenous mixtures look the same throughout • Types: solutions, alloys, etc. • Example: salt water, brass

18. Indicators of Homogenous Mixtures • Have the same composition throughout • Components are indistinguishable • Will not scatter light • Particle size is small

19. Can they still be separated by physical means ? YES!!! It may be more complicated, but it can be done…distillation , centrifugation

20. Homogeneous mixtures are called solutions • Solutions are … • homogenous mixtures that do not scatter light. • separated by physical means (including distillation or evaporation.) • created when something is completely dissolved in pure water. • Examples: sugar water, salt water

21. Parts of a Solution • Solute- substance that dissolves in solvent • ex. Salt (“U dissolve”) • Solvent- substance that does the dissolving (ex.water) Well, not really, because you don’t dissolve, but you get the picture 

22. Why don’t you dissolve? • You are not “Miscible” • Miscible- two or more liquids that can dissolve into each other • Immiscible- liquids that do NOT mix • Ex- oil and water

23. Heterogenous Mixtures Heterogeneous mixtures are composed of large pieces that are easily separated by physical means (ie. density, polarity, metallic properties).

24. Indicators of Heterogenous Mixtures • Do not have same composition throughout • Components are distinguishable • Particle size is medium or large Examples: fruit salad, vegetable soup, etc.

25. Tyndall Effect • Scattering of light due to particles

26. Types of HeterogenousMixtures 1. Colloid –medium particles • Particles stay suspended in the mixture and scatter light (Tyndall effect) • Ex- mayonnaise, milk, fog

27. Types of HeterogenousMixtures 1. Suspension- large particles • Tyndall effect • Particles will settle out when the mixture is allowed to stand • Ex-muddy water, OJ with pulp

28. What kind of changes does matter undergo? Physical Chemical

29. physical properties • Physical properties are those that we can determine without changing the identity of the substance we are studying. • Properties we can observe or measure • Ex- color, state of matter, etc

30. Physical Properties of Matter

31. Physical Properties of Matter

32. DENSITY Mass per unit volume Calculated by: Density= Mass/Volume D=M/V

33. Physical Properties of Matter

34. Examples of physical properties: • Hardness, color, melting point and density are all physical properties. • The physical properties of sodium (NaCl) metal • soft, lustrous • silver-colored metal • relatively low melting point • low density.

35. What is a physical change? • A physical change occurs when the substance changes physically but does not change its chemical composition. • For example: water freezing into ice, cutting a piece of wood into smaller pieces, etc. • The form or appearance has changed, but the properties of that substance are the same (i.e. it has the same melting point, boiling point, chemical composition, etc.)

36. Temperature Melting Boiling Freezing Color Conducting electricity Dissolving Physical Changes

37. What are chemical properties? • Chemical properties describe the way a substance can change or react to form other substances. • These properties, then, must be determined using a process that changes the identity of the substance of interest.

38. How can chemical properties be identified? • One of the chemical properties of alkali metals such as sodium and potassium is that they react with water. To determine this, we would have to combine an alkali metal with water and observe what happens. • In other words, we have to define chemical properties of a substance by the chemical changes it undergoes.

39. What are chemical changes? • A chemical change occurs when a substance changes into something new. • This occurs due to heating, chemical reaction, etc. • You can tell a chemical change has occurred if the density, melting point or freezing point of the original substance changes. Many common signs of a chemical change can be seen (bubbles forming, mass changed, etc).

40. You can’t go back to the original substances after a chemical change (reaction) has occurred!! Characteristics of Chemical Changes Baking soda reacting w/ vinegar Burning wood

41. Comparison of Physical and Chemical Properties

42. Law of Conservation of Matter There is no observable change in the quantity of matter during a chemical reaction or a physical change. In other words, matter cannot be created nor destroyed. It is just converted from one form to another