Unit 1: Matter & Change

Transcription

1 Unit 1: Matter & Change

2 Classification of Matter Pure Substances Matter anything composed Mixtures of atoms Elements Compounds Heterogeneous Mixtures Homogeneous Mixtures

3 Pure Substances Element: one of the 109 pure substances that cannot be separated by chemical change or physical change. Represented by a symbol on the periodic table. Examples: gold (Au), hydrogen(h), potassium (K) Compound made from atoms that are chemical bonded together. Can be separated by chemical change, but not physical means. Represented by a formula. Examples: H 2 O (water), CO 2 (carbon dioxide), NaCl (sodium chloride)

4 Separation of Compounds: Molecules can be divided into atoms of the elements that make them up, but only through a chemical change. In electrolysis (for example), the bonds of H 2 O are broken and the two gases, oxygen and hydrogen, are no longer connected to one another. The indicator in this reaction is the formation of gas bubbles. The physical and chemical properties of these two elements are completely different than the properties of water!!!

5 Mixtures Mixture: two or more pure substances that can be separated by physical changes

6 Mixtures Homogeneous Mixture: two or more pure substances mixed evenly. When you look at it, you can t see separate parts. Also called solutions Examples: salt water, soda, coffee,

7 Mixtures Alloy a homogeneous mixture made by melting two or more elements together, at least one of them a metal. Example: brass, steel, 14k gold

8 Mixtures Heterogeneous Mixture: two or more pure substances mixed unevenly (you can see the different components). Example: fruit salad, pizza, granite

9 Suspensions Heterogeneous mixture A suspension has large particles that will stay mixed up (or suspended) for as long as the mixture is in motion Once the motion stops, the particles will fall to the bottom or settle out can be separated through filtering Ex: sand water, Italian salad dressing

10 Colloids Somewhere between a solution and suspension Heterogeneous mixtures where the medium sized particles are dispersed throughout but are not heavy enough to settle out. Appear cloudy and opaque Cannot be separated by filtering Ex: milk, fog, blood, jello

11 How can light be used to tell the difference between colloids and solutions? Tyndall effect A beam of light passing through a solution, such as air, is not visible. Light passing through a colloid, such as fog, will be scattered by the larger particles and the light beam will be visible.

12 How can mixtures be separated? Remember, mixtures can only be separated physically. Magnetic Separation-Used to separate particles based on magnetic properties. Evaporation-Used to separate a dissolved solute from a solution. Sieving-Used to separate particles of different sizes by passing through a mesh or net

13 Filtration Used to separate a solid from a liquid. The liquid (and anything dissolved in the liquid) passes through holes in the filter paper, but the solid particles are too big and get stuck. Example: using a filter to separate dirt from water

14 Decanting The separation of mixtures leaving sediments in the bottom of the original container The liquid is poured into a new container without disturbing the sediment or lower liquid layers.

15 Centrifugation Separating liquids of different densities or solids from liquids by the application of centrifugal force Example: separating blood into plasma and blood cells

16 Distillation Used for separating Mixtures based on differences in the conditions required to change the phase of components of the mixture. Example: ethanol (ethyl alcohol) can be separated from water by distillation because ethanol has a lower boiling point than water

17 Chromatography Used to separate a mixture on the basis of differences in their affinity for a stationary and a mobile phase Example: separating components of ink using paper (stationary phase) and water (mobile phase)

18 Crystallization A solid-liquid separation technique through the formation of solid crystals from a homogeneous solution

19 Homework Page 4 and finish MSDS Project

20 Physical and Chemical Properties and Changes of Matter

21 All Matter has Properties A physical property can be observed without a chemical change occurring. A chemical property can be observed only when a chemical change occurs

22 How many can you remember? Physical Properties Color Shape Texture Viscosity Buoyancy Mass Volume Weight Density* (mass/volume) Chemical Properties Flammability Ability to rust Reactivity Enthalpy of formation

23 Physical & Chemical Changes A Physical change is one that does not result in the production of a new substance. You can often undo these changes. Ex. Mixing salt and water together gives you salt water, but you still have salt and you still have water. You can separate them out again. Ex. If you melt ice, you still have water. You can undo this and freeze it back. No new substance is made, it's still just water.

24 Physical & Chemical Changes Chemical A change is one that results in the production of another substance and is often seen as a change in color, odor, temperature, or the production of gas bubbles. You cannot undo these changes. Ex. Burning a piece of firewood. That charred black remnants of a log is no longer wood it's a new substance. Ex. A penny turns green. The coating of green patina is a new substance as the copper in the penny oxidizes, reacting with the oxygen in the atmosphere in the presence of air moisture.

25 Physical Change in the Water Cycle

26 Physical vs. Chemical Changes Examples of Chemical Changes: burning, rusting, decaying, digestion

27 Four indicators of a chemical change 1. Energy Change heat or light is produced, or a decrease in temperature. Exothermic gives off heat, feels hot Endothermic takes in heat, feels cool.

28 Four indicators of a chemical change 2. Production of a gas (you see bubbles or fizzing)

29 Four indicators of a chemical change 3. Precipitate a solid is formed when two liquids are mixed together. The indicator that a precipitate has formed is that the liquid turns cloudy.

30 Four indicators of a chemical change 4. Color change (usually happens) Think of digestion which is a chemical change

31 Rock Cycle The rock cycle has both physical and chemical changes occurring. Physical: rocks are weathered by wind and water, but the small pieces of rock have not changed composition. Chemical: acid rain can react with limestone, changing the chemical composition of the rock.

32 Rock Cycle

33 Digestion The digestion of food is an example of both a physical change and a chemical change. 1 st you chew, creating smaller pieces physical change 2 nd your saliva has an enzyme that breaks down starch chemical change 3 rd pepsin (stomach) breaks down protein, bile (sm. intestine) acts on fat chemical change End of day 2 HW page 7

34 Measurable Properties Extensive Property a measurable property of a sample of matter that depends on how much of the matter is being considered. Examples: mass, volume Intensive Property a measurable property of a sample of matter that does not depend on how much of the matter is being considered. Examples: Color, Density

35 Density depends on two things: 1. How tightly packed the atoms are 2. What kind of atoms they are If the black dots are atoms, which box represents the substance with the greatest density?

36 Useful Density Information Density of water = 1 g/ml Objects with a density greater than 1 g/ml sink in water Objects with a density less than 1 g/ml float in water

37 Teacher Demo with Paper When your teacher cut the piece of paper in half, what happened to the mass of the paper? When your teacher cut the piece of paper in half, what happened to the volume of the paper? If the original mass of the paper was 8.0 g and the original volume was 2.5 cm 3, what was the original density of the paper? (Show your work) Assuming the information given above is correct, what would the NEW density be for just one half of the original piece of paper? (Show your work) When your teacher doubled the amount of water in the beaker, what happened to its mass? When your teacher doubled the amount of water in the beaker, what happened to its volume If the original mass of the water was g and the original volume was 150 ml, what was the original density of the water? (Show your work) Assuming the information given above is correct, what would the NEW density be for double the original amount of water? (Show your work)

38 Density is calculated with the formula: Find it!

39 Density Calculations What do you do? G iven what do you know? Write it down. U nknown what are you looking for? x =? E quation which one are you going to use? S ubstitute substitute in the correct values with units. S olve work the problem with your calculator. **Don t forget to your answer with the correct number of sig figs and correct units.

40 Let s Practice! 1. What is the density of a piece of wood that has a mass of g and a volume of cm 3? 2. A metal cylinder is placed into a graduated cylinder with 24.0 ml of water. After the cylinder is added, the volume of water rises to 30.4 ml. The density of the cylinder is known to be 8.9 g/ml. What is the mass of the cylinder?

41 Kinetic Molecular Theory Atoms and molecules are constantly moving, and we measure the energy of these movements as the temperature of the substance. The more energy a substance has, the more molecular movement there will be, and the higher the perceived temperature will be.

42 States of Matter

43 There are three states (also called phases) of matter. The picture represents the same chemical substance, just in different states.

44 There are three states (also called phases) of matter. Solid Matter that has both a definite shape and definite volume. Molecules or atoms are very close together and can only vibrate a little. They do not move past each other.

45 There are three states (also called phases) of matter. Liquid: Matter that has a distinct volume but no specific shape. Molecules or atoms are close together. Have the ability to slide across one another very easily.

46 There are three states (also called phases) of matter. Gas: Matter that has no fixed volume or shape. It conforms to the volume and shape of its container. Its molecules or atoms are very far apart from each other and move very fast.

47 Density Comparison If you consider the solid, liquid, and gas state of one particular substance, this rule holds true in most cases: Solid is more dense than liquid Liquid is more dense than gas

48 Water is Weird A notable exception is water! The solid state of H 2 O, ice, is less dense than liquid water. This is why ice floats. This is true because of the way hydrogen bonds form when liquid water freezes. The hexagonal pattern results in empty space between the molecules.

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50 CORE Concept Melting Condensation Vaporization Freezing Sublimation Deposition

51 CORE Concept Write an example Write the definition Condensation Vaporization Freezing Sublimation Deposition

52 Phase Changes That Require Energy (increase in temperature, endothermic) Melting: solid liquid Ex: ice melting to liquid water Vaporization: liquid gas Ex: heating water on the stove, steam is released. Sublimation: solid directly to gas Ex: dry ice (solid CO 2 ) lets off CO 2 gas, looks like steam; solid air fresheners.

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54 Phase Changes that Release Energy (decrease in temperature, exothermic) Condensation: gas liquid Ex: sweat collects on a cold glass of ice water. Freezing: liquid solid Ex: water freezing into ice. Deposition: gas directly to solid Ex: frost forms on the grass on a cold morning, snowflakes form from water vapor in clouds.

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56 Endothermic Phase Changes That Require Energy (increase in temperature) CORE Concept Melting Vaporization Sublimation Condensation Freezing Deposition Phase Changes that Release Energy (decrease in temperature) Exothermic

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