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Pure Substances vs. Mixtures Physical and Chemical Changes

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Presentation on theme: "Pure Substances vs. Mixtures Physical and Chemical Changes"— Presentation transcript:

1 Pure Substances vs. Mixtures Physical and Chemical Changes
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? Everything that has mass and takes up space is called matter. Basic definition of 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 What is a pure substance?
Compounds Molecules made by two or more elements bonded together -always in a definite ratio Elements Molecules made of just one element The two categories of pure chemical substances. 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 Basic characteristics of pure substance:


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. Basic identification of a mixture. 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 Brainstorm more examples of homogenous mixtures.

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. Brainstorm more examples of heterogenous mixtures.

25 Tyndall Effect Scattering of light due to particles

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

27 Heterogenous Mixtures
Types of Heterogenous Mixtures 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
Property Description Example Hardness Ability of 1 substance to scratch another Diamond can scratch glass Viscosity Resistance to flowing Water= low visc. Honey= high visc. Solubility Ability to dissolve in water NaCl dissolves easily in water so it’s soluble

31 Physical Properties of Matter
Property Description Example Superconductor Substance that conducts electricity at lower temperatures Tin, aluminum, used in trains Semiconductor Substance that has a resistance b/w a conductor & insulator Silicon-used in computers or radios

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.) Definition of physical changes.

36 Physical Changes Temperature Color Conducting electricity Dissolving
Melting Boiling Freezing Color Conducting electricity Dissolving Physical changes are characterized by the following:

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). Definition of chemical change.

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

41 Comparison of Physical and Chemical Properties

42 Conservation of Matter
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 Definition of Conservation of matter.

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