CLASSIFICATION OF MATTER

Transcription

1 Unit 2 Matter and Energy Topic 2.1 Properties and Changes of Matter name Essential Question: What kinds of matter are there, and how can you turn one form of matter into another? Chemistry - The study of MATTER the CHANGES matter undergoes, and the ENERGY associated with those changes. Matter - Anything that exists that has definite MASS and occupies a definite VOLUME. CLASSIFICATION OF MATTER

2 Substances (elements and compounds) are all HOMOGENEOUS (containing the same composition of material throughout the sample). Elements are substances that cannot be decomposed by chemical change. They are made up of ATOMS. Element symbols are either one letter, which is capitalized, or two letters the first one capital, the second lower-case. Examples of elements: One letter: O (oxygen) Two letters: Ni (nickel) Note: Cl is chlorine. C followed by a lower-case L. Compounds are substances that are made of elements chemically bonded to each other, and can be decomposed by chemical change back into separate elements. Examples of compounds: NaCl (made of sodium and chlorine) Cu 3 (PO 4 ) 2 (made of copper, phosphorous and oxygen) Mixtures are combinations of substances that are not chemically combined together, and they can be broken apart by physical change. Homogeneous mixtures are called SOLUTIONS. Examples of these mixtures include: 1) Aqueous solutions: NaCl (aq) Aqueous means that the solute (NaCl) is dissolved into WATER. Aqueous Solutions identified with two letters (AQ) This is an example of a SOLUTION. It can not be separated by filtering. To separate the salt from the water, you must evaporate the water. Solutions are TRANSPARENT (you can see through them). 2) Tinctures: a solution where the solute is dissolved in alcohol (ethanol). Some things which cannot dissolve in water can dissolve in alcohol. This includes tincture of iodine, which is used to disinfect cuts. It consists of iodine dissolved into alcohol. 3) Amalgam: a solid solution where a metal is dissolved into mercury (Hg). Metals commonly used to make amalgams with mercury are silver (Ag) and gold (Au), which used to be used for dental fillings until porcelain and composite substances became more widely used for that purpose. 4) Alloys: metals can not chemically bond with each other, but they can be mixed together to enhance their properties. Iron (Fe) is a strong metal that is useful for making into structural shapes, but it does have drawbacks. It can rust and it is quite soft. Mixing in carbon (C) makes an alloy known as steel. This steel can be further enhanced by adding yet more metals, like chromium (Cr), molybdenum (Mo) or cadmium (Cd). Gold is pretty to look at, but it is too soft on its own to fashion durable jewelry. 24 karat gold is pure gold, 14 karat gold is more than half pure gold, but silver (Ag) and copper (Cu) are added to make the gold item more durable. 18 karat white gold is an alloy of gold, palladium, nickel and zinc, or gold and platinum or palladium.

3 Heterogeneous (varying composition throughout the sample) mixtures include: 1) Muddy water. The composition towards the bottom is mostly mud, towards the top it s mostly water. When shaken, the particles will never be dispersed evenly enough to be considered homogeneous. 2) Italian salad dressing: The different ingredients separate by density with the oil on top and the vinegar and water at the bottom with various pieces of chopped garlic and pepper at different levels with varying concentration. As with muddy water, the particles are too large to form a homogenous mixture. 3) Soil: this contains microscopic rock fragments, organic debris and other items, depending on where you find it. 4) Cat vomit: this amazing material can contain a wide assortment of components, including partially digested dry or wet food, stomach juices, animal bones, fur and other items which vary widely from cat to cat and from vomit to vomit. These components are not mixed together regularly, upon examination of the vomit pile, one might see more fur on one side and more crunched-up dry food on the other. Particle Diagrams: These show how the forms of matter look in a simple diagram form. Elements: single atoms, not bonded to each other. Diatomic Molecule: certain elements are so reactive that they are more stable as pairs, forming two-atom molecules that are called diatomic. The elements that do this are Br, I, N, Cl, H, O and F. Their formulas are written as Br 2, I 2, N 2, Cl 2, H 2, O 2 and F 2. Since they are made of only one element, they are not considered to be compounds. Compounds: These are made of two or more different elements chemically bonded together in a definite, whole-number ratio. Three phases of matter solid liquid gas

4 Homogeneous mixtures: These are combinations of elements, compounds or both, in no fixed ratio, and not bonded together, but evenly dispersed throughout the volume of the mixture. Heterogeneous mixtures: These are combinations of elements, compounds or both, in no fixed ratio, and not bonded together, but unevenly dispersed throughout the volume of the mixture. Guided Practice Pure Substance Element or Compound Phase C 12 H 22 O 11 (s) Fe (s) Br 2 (l) CO (g) Au (s) Co (s) He (g) Identify the following as HOMOGENEOUS or HETEROGENEOUS mixtures by placing a check underneath the appropriate heading. Soil Air (clean) KCl (aq) MIXTURE HOMOGENEOUS HETEROGENEOUS Chocolate Chip Cookie 22 K Gold

5 H 2 H 2 O NaCl (aq) Which contains a single substance? How many elements are present in each molecule of water in the bottle (b)? What is the ratio of hydrogen to oxygen in the molecule of water? As you know, ice is frozen water. In other words, ice and water is the same substance in two different phases of matter. What do you expect the ratio of hydrogen to oxygen atoms to be in a molecule of ice? Which bottles on the picture contains a mixture? How do you know that? Which substance that could be broken down physically? Which bottle on the picture contains substance that could be broken chemically? How do you know? Which bottle on the picture contains substance that could not be broken chemically or physically?

6 Topic 1: Properties and Changes of Matter-Read the section and fill in the chart below with the important points presented Include examples & sketches Pure Substances Mixtures Elements Compounds Homogeneous Mixtures Heterogeneous Mixtures Examples Examples Examples Examples Sketch: Sketch: Sketch: Sketch: Notes Notes Notes Notes

7 Properties of Matter Topic 2.1 A) Physical Property (PP): characteristics or traits that can be observed without changing the chemical identity (Observed many times through a physical change) Physical Change (PC) changes only the appearance not the chemical identity of the substance; can be reversed by another physical change B) Chemical Property: properties, which change the chemical identity of a substance; observed through a chemical change. (Or lack of chemical change) Chemical Change (CC): change which results in a new chemical substance being formed, can be reversed ONLY by another chemical change NOT a physical change Flash from Past: In biology (Living Environment) you learned that digestion was both physical and chemical. Give an example of a physical change and a chemical change that food undergoes when you digest it. Physical Change: Chemical Change: Let s brainstorm your own examples of physical and chemical properties and changes Physical properties and changes Chemical properties and changes

8 1) Predict the Type of Change Ask yourself if a NEW CHEMICAL SUBSTANCE is formed If yes, than it is a CHEMICAL CHANGE If no, then it is a PHYSICAL CHANGE A PHYSICAL CHANGE can easily be reversed by another PHYSICAL CHANGE EXAMPLES Predictions This is actually Type of change needed to reverse Pulling the steel wool Battery producing electricity Touching battery terminals with steel wool Dissolving sugar Melting Wax Burning Wax Melting Ice Dissolving NaCl in water Mixing Zn and HCl (aq) Mixing KI (aq) and AgNO 3 (aq) Conclusions: 1) Why your three examples have proven to be a PHYSICAL change 2) Why you three examples have proven to be a Chemical changes Guided Practice: Identify the following as PC or CC: 1) Change from a solid to a liquid 2) Cooking Meat

9 3) Dissolving sugar in tea 4) Baking Bread 5) Turning water into ice in the freezer 6) Decaying leaves 7) Lighting a match 9) Rusting of your car 2) Energy Topic 2.2 8) Boiling Water 10) Combustion (burning) of wood Essential Question: What are the forces at work in the universe that make things happen? Energy: The ability to do WORK which is using FORCE to move an object a DISTANCE. 1) Kinetic Energy: Energy of MOTION, contained by anything that MOVES. Atoms, molecules and other particles of that scale move faster when TEMPERATURE is increased. Celsius: Devised by Anders Celsius (~1742): Based on setting the melting point of water as 0 o C and the boiling point of water as 100 o C. Kelvin Scale: Devised by Lord William Thompson Kelvin: He used the Celsius-sized degree, but he reset the scale so that it starts at 0 Kelvins. At this temperature (which is also -273 o C), all particle motion stops. To convert back and forth between Celsius and Kelvin temperatures: Melting point of water, 0 o C is equal to 273 K ( = 273) Boiling point of water, 100. o C is equal to 373 K. ( = 373)

10 2) Potential Energy: STORED energy, energy that s not doing work right now, but it has the ability to if released. Found in coiled springs, chemical bonds (batteries, explosives, chemical hot packs), objects at a height above gravity, magnetism (both attraction and repulsion) Measurement: Since stored energy cannot be directly measured, it must be converted to KINETIC energy and measured using a CALORIMETER. JOULE (J): The metric unit for potential energy Joules is a kilojoule (kj), and is the unit most often used to measure potential energy changes in chemical and physical changes (such as burning, melting and so on). 3) Heat Flow Heat flows from where it s HOT to where it s NOT. Examples: 1) Open the front door of your nice warm house on a cold winter morning. The heat will flow from your house out into the cold air. 2) Place a hot pack on a sore muscle to soothe it. The heat will flow from the hot pack into the muscle. 3) Place a 45 o C piece of warm metal into a beaker of water at 10 o C. The heat will flow out of the metal into the water. LAW OF CONSERVATION OF ENERGY Energy cannot be created nor destroyed by physical or chemical change, only converted from one form of energy into another. C. Flow of Energy: Heat moves only, cold does not move!!!!! Energy flows from a object to a object ONLY

11 Example: Cold kitchen floor and warm feet. Heat energy flows from the warmer feet to the cold floor. As a result, your feet become cooler ( T ) and the floor becomes warmer (T ). Temp of A Heat Flow Temp of B Temp of A Heat Flow Temp of B 15 C 35 C 10 C 293 K 30 C 25 C 30 C 283 K 10 C 10 C 303 K 5 K 45 C 65 C 5 K 5 C Use an arrow ( or or ) to show the direction of heat (energy) flow between the objects, A and B, for the given temperatures Hint: If the temperature scales are not the same, convert one scale so you can compare the different temperatures more easily. (I usually convert K since adding is easier!) Measuring Changes in Potential Energy by using Changes in Kinetic Energy a.) Hot / Cold Pack When a substance dissolved in water energy is either released to or absorbed from the surrounding water. This is the basis of some hot and cold packs found in first aid kits. Two types of demonstrations will be done. Record the data below and determine the type of reaction (endo or exo) Data Table Demo #1 Demo #2 Mass of H 2 O used Initial Temperature (T i ) Final Temperature (T f ) Change in (difference in) Temperature ( T) Endo or Exo When the dissolving of a substance releases energy, the temperature of the solvent, water, increases. This is known as an exothermic (exo) process. The energy exits the substance. Exothermic Temp of H 2 O

12 q Heat, potential energy that was released to or absorbed When the dissolving of a substance absorbs energy, the temperature of the solvent, water, decreases. This is known as an endothermic (endo) process. The energy enters the substance. Endothermic Temp of H 2 O If the energy is absorbed by (added) to the water, the temperature will. If the energy is released (removed) from to the water, the temperature will. Calorimetry Topic 2.3 Now the fun begins How do we relate the temperature change to the change in the potential energy?? By using math, of course!!! This is known as calorimetry. Calorimetry is the measurement of heat change. A calorimeter, which is an insulated device, would be used, rather than a plastic baggie, to run the reaction or to dissolve the substance. Example of everyday calorimeters: Reference Table T: Calorimetry Formula

13 by the water m How much water used c T *Specific heat of water *Given on Ref Table B *How many joules are needed to change the temperature of 1 g of a substance (water) by 1 o C Absolute value (+) of the difference in the initial (T i ) and final (T f ) of the water T f -T i Calorimetry practice q= 1. How many joules of heat are required to raise the temperature of 20.0 grams of water from 30.0 C to 40.0 C? m= c= T= 2. How many joules of heat are needed to raise the temperature of a 4.00 gram sample of water by 18.0 C?

14 3. How many grams of water will absorb a total of 418 Joules of energy when the tempearutre of the water changes from 10.0 C to 30.0 C? CALORIMETRY PRACTICE PROBLEMS: No work, No Credit!! 1. a) How many joules must be absorbed by 50.0 grams of water for the temperature to change by 15 C? b) How many kilojoules is your answer in 1a? (Use the factor label method!) 2. a) If joules are added to 100. grams of water at 10.0 C, what will the change in temperature be? b) What will the new temperature be in problem 2a?

15 3.a) If the temperature of a sample of water changes by 25.0 C when joules are removed, what is the size (mass) of the water sample? b. If the initial temperature of the water sample was 55 C, what was the final temperature of the water in 3a? 4. The directions on a British tea bag say to heat the cup of water to 100. C before adding the tea bag. How many joules must be added to 150. g of water to raise the temperature of the water from 24 C to the suggested temperature? 5. A woman in New Mexico sued McDonald s over burning herself with coffee that is served there. Use the following assumptions: a) the coffee has the same specific heat as water (4.18 joules/g C) b) the size of the coffee was 200. g c) the initial temperature of the coffee was 85.0 C d) the final temperature of the coffee was 36.0 C (outside body temperature) i.) Calculate the number of Joules that burned the woman ii.) How many kilojoules is your answer? Use the factor label method. iii) What are the initial and final temperatures on the Kelvin scale? (See reference table T if you forgot how to do this) Must show work! Initial Temperature: Final Temperature:

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