2.1 Classifying Matter

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Rodger Lawrence
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1 2.1 Classifying Matter EVERYTHING (so far) ENERGY - no mass/volume. Sound, heat, and light are good examples. MATTER - anything which has mass and volume (takes up space). MIXTURE - made of multiple (different) particles. Not pure, but may appear to be so). SUBSTANCE - made of just one type of particle. Pure or chemically-bonded. HETEROGENEOUS MIXTURE - clearly made of two or more different materials. Examples: you, most food, mud, etc. HOMOGENEOUS MIXTURE - so well mixed, appears to be pure until you get to the particle level. Examples: anything dissolved, air, alloys. COMPOUND - two or more bonded atoms. Will have a chemical formula. Examples: H 2 O, CO 2 ELEMENT - made of only one type of atom. Only one symbol. Examples: Fe, O, P 4, Cl 2 Increasing purity at the PARTICLE-LEVEL ~ 1 ~

2 Particle-level diagrams are used to show the make-up of a material down to the molecular or atomic level. In these diagrams, atoms are shown as single spheres: Bonded atoms are grouped together and known as molecules: Elements: He(g) - Helium gas O 2 (g) - Oxygen gas Compounds: H 2 O(l) - water SF 6 (g) - sulfur hexafluoride gas Mixtures: - + NaCl + H 2 O - salt water (homo) "Muddy" water (het) ~ 2 ~

3 Ex.1) Classify each of the PLDs below as showing elements, compounds, or mixtures: A.) B.) C.) D.) Ex.2) a.) c.) b.) d.) ~ 3 ~

4 Mixtures can be separated physicallly (evaporation, forceps, etc), while compounds can only be separated chemically (high heat, chemical rxns). Elements cannot be separated by either method. How would you classify... Ex.3)...a blue fluid if it leaves behind a solid blue residue when boiled? Ex.4)...a reddish metallic substance which does not separate in reactions, melts under extreme heat, and reacts to form a black solid with oxygen gas? Ex.5)...a stone with multiple bands of colored layers? Ex.6)...a pure white crystalline material which produces a green gas and molten metal at extreme temps? ~ 4 ~

5 Each of the problems below discusses a different type of matter. Use the observations provided to classify each correctly: E, C, Het M, Hom M Ex.7) An unknown solid has a smooth, metallic appearance. When exposed to air, it tarnishes to a dark black and becomes brittle. Extreme heating causes this material to melt, but produces no other obvious changes. When cut into pieces, the density of each piece is identical to the others. Ex.8) When collected by a mining truck, a sample of iron ore displays a variety of colors and textures. Ex.9) A bluish-green powder dissolves cleanly in water and cannot be separated by forceps or evaporation. Strong heating, however, produces a black powder and a foul-smelling gas. Ex.10) A liquid is clear throughout and shows no obvious impurities. When evaporated, a crystalline white residue is left behind. ~ 5 ~

6 In a separate tab, look up each of the following materials. Classify each as energy (X), elements (E), compounds (C), heterogenous mixtures (Het M), or homogenous mixtures (Hom M): rust / sound / choc. chip cookies / milk / gold C X Het M Hom M E Ex.11) chlorine gas / water / soil / oxygen gas Ex.12) carbon dioxide / salad / lead / air / light Ex.13) sand / pizza / rocky road ice cream / sodium Ex.14) fizzy and flat soda / heat / plutonium / 18 kt gold Ex.15) brass (alloy - know me!) / phosphorus / wood ~ 6 ~

7 2.2 The Properties of Matter We use properties to describe matter in a variety of ways, most of which should be familiar to you. We'll begin with basic properties: Physical - appearance, weight, etc. These properties can be measured or observed without destroying/reacting the substance being studied. Chemical - abilities. The material being studied is changed or destroyed when these are tested. In addition, all properties are either: Intensive - based ONLY on IDENTITY. Cutting something in half would not change this. Extensive - based ONLY on QUANTITY. Cutting something in half would change this property. ~ 7 ~

8 Classify each of the properties described below as physical / chemical and intensive / extensive. Ex.1) Mass - 34 g, kg Ex.2) Flammability - will it burn? Ex.3) Color - blue, red, chartreuse, etc. Ex.4) Solubility - will it dissolve in...(water, etc)? Ex.5) Volume ml, 2.0 gallons, 36 cm 3 Ex.6) Conductivity - thermal or electrical Ex.7) Reactivity with... (water, oxygen, etc) Ex.8) State (solid, liquid, gas) at room temperature Ex.9) Malleability - can it be flattened into sheets? Ex.10) Dimensions - (length, width, height) ~ 8 ~

9 Ex.11) Michael notes that a sample of copper......conducts electricity...displays luster...has a mass of 480 g... is reddish brown....displaces 220 ml of water in a graduated cylinder Ex.12) Jose uses the following properties to describe sulfuric acid, H 2 SO4: Clear, pale yellow Highly viscous (syrupy) Corrodes iron Boils at 120 C Ex.13) Pure oxygen, O 2,......is a gas at room temperature, 25 C ( / )...is highly reactive with most metals, ( / )...liquifies at -219 C ( / )... does not conduct electricity, ( / )...and has a density of g/ml. ( / ) ~ 9 ~

10 2.3 Density Calculations Density describes how tightly "packed together" particles (atoms, molecules, etc) within a compound are found. Iron Metal, Fe Oxygen Gas, O 2 (More Dense) (Less Dense) > Given an equal volume of iron Fe(s) O 2 (g) metal and oxygen gas, the iron would have a much higher mass due to its significantly higher density. Fe(s) = O 2 (g) (therefore) equal masses of iron and oxygen would have different volumes. ~ 10 ~

11 Ex.1) Assuming you are given equal volumes of each of the following materials, circle the one with the greatest mass: Water and styrofoam Wood and iron Copper and air Helium and silver Ex.2) Given equal masses of each material, which would have the greatest volume? Water and styrofoam Wood and iron Copper and air Helium and silver Ex.3) Which material (from each pair) has the greatest density and is more compressed? Water and styrofoam Wood and iron Copper and air Helium and silver ~ 11 ~

12 Density is calculated by dividing a substance's mass (typically in grams, g) by its volume (typically in ml or cm 3 ). The greek symbol "rho" is used for density: Ex.4) Solve the density equation for both "m" and "V": m = V = Ex.5) Calculate the density of iron if a sample has a mass of g and a volume of ml: Ex.6) Titanium has a density of 4.5 g ml -1. What is the volume of a titanium sample with a mass of 12.6 g? ~ 12 ~

13 When working in lab, mass is easily determined with an electronic balance. To determine volume, especially for unusually-shaped objects, we use the concept of water displacement as shown below: The difference between the initial (starting) and final volumes is the volume of the object. V = V f - V i Ex.7) What is the volume of the rock in the image above? Ex.8) A gold nugget has a mass of g according to the electronic balance in lab. When placed in a graduated cylinder containing ml of water, the new reading is ml. Calculate the density of gold: ~ 13 ~

14 You should also be able to handle unit conversions within density problems. Remember: 1000 g = 1 kg, 1000 ml = 1 L, and 1 ml = 1 cm 3 : Ex.9) A massive sample of helium gas has a mass of 0.98 kg and occupies 5,444 L. Calculate its density in g/ml: Ex.10) Crude oil has a density of 0.88 g ml -1. Determine the mass of an oil tanker, in kg, if it carries 5.03x10 8 L of crude oil. ~ 14 ~

15 Density is specific to a material and does NOT change when a pure substance is cut apart, etc. In other words, a pure copper penny would theoretically have the same density as the entire Statue of Liberty. Ex.11) A sheet of copper with a mass of 270 g and a volume of 30.0 ml is cut in half and then into ten equal pieces. Determine the mass, volume, and density of the copper pieces at each point in this process: Original: Halves: Tenths: m = m = m = v = v = v = ρ = ρ = ρ = Ex.12) According to the calculations above, density (DOES / DOES NOT) change when a material is cut apart. density is a (PHYSICAL / CHEMICAL) and (EXTENSIVE / INTENSIVE) property. ~ 15 ~

16 2.4 Physical and Chemical Change Physical Change: Does not create a new substance. Affect appearance, shape, etc, but NOT identity. Phase changes are examples. Chemical Changes Makes something completely NEW via a chemical reaction. Look for: color/temperature changes, and/or formation of bubbles/precipitates. The signs above indicate a chemical change ONLY when there is no valid physical explanation: Ex.1) Water with blue food dye is placed onto a hot plate and mixed with red food dye. The mixture begins to bubble and turns purple. Which type of change, physical or chemical, has occurred? ~ 16 ~

17 Ex.2) Two clear mixtures are poured together to form a solution (mixture dissolved in water). After a few minutes, the solution turns a deep bluish-black and releases a strong antiseptic odor. Which type of change, physical or chemical, has occurred? Ex.3) A dense silver liquid is removed from a hot water bath and placed on the lab table. After about 30 minutes, it becomes a lustrous silver solid. Which type of change, physical or chemical, has occurred? Ex.4) Classify the verbs below as physical or chemical: Burning - Freezing - Chopping - Boiling - Rusting - Rotting - ~ 17 ~

18 Correctly identify each of the following as a chemical or physical change. Ex.5) Sugar, salt, and alcohol dissolve in water. Ex.6) Limestone, CaCO 3, releases CO 2 gas as it is heated. Ex.7) Copper metal melts at a temp of 1984 F (1085 C) Precipitation is a unique form of chemical reaction in which two dissolved substances react to form an insoluble substance. This substance becomesa solid, sinks to the bottom, and is known as a precipitate. Clear solutions will often becomee cloudy when this occurs. ~ 18 ~

19 Ex.8) You add two dissolved chemicals together in a test tube. The water clouds and a fine yellow powder settles to the bottom. Ex.9) A soil sample is added to a beaker of water and stirred vigorously, causing the water to become cloudy. Over time, a fine brown powder settles to the bottom of the beaker. Ex.10) Classify the following verbs as chemical or physical: Chewing - Reacting - Filtering - Condensing - Digesting - Corroding - Ex.11) Baking soda is mixed into a solution of vinegar at room temperature. Small bubbles begin to appear and fizz near the top. ~ 19 ~

2.5 Phase Changes and States of Matter Matter is held together by what are known as intermolecular forces or IMFs, a topic we'll discuss in much greater depth in Unit 4.

20 2.5 Phase Changes and States of Matter Matter is held together by what are known as intermolecular forces or IMFs, a topic we'll discuss in much greater depth in Unit 4. Particles with opposite charges (+/-) are a simple example. Water's fairly strong IMFs make it a liquid. (Hydrogen bonding) On the other hand, the energy of matter causes particles to vibrate. We refer to this as a material's kinetic energy or KE. A substance's average KE is measured through what you know as temperature. These vibrations act to "shake apart" matter, in the same way a cell phone "skitters" across a table. Increasing Temperature ~ 20 ~

Increasing KE / Vibrations / Temperature Solids: IMFs >> KE. Particles are rigidly locked together, vibrating in place. Definite volume and definite shape. Liquids: IMFs > KE.

21 Increasing KE / Vibrations / Temperature Solids: IMFs >> KE. Particles are rigidly locked together, vibrating in place. Definite volume and definite shape. Liquids: IMFs > KE. Particles vibrate enough to "slide around", but are still pressed together tightly. Definite volume, but shape becomes indefinite. Gases: IMFs KE. Particles vibrate enough to break free of all IMFs and "fly apart". Both volume and shape become completely indefinite. Plasma: IMFs <<< KE. Forms when gases become superheated. Gas particles become charged ions (+/- particles). Flame and electrical arcs are good examples. Shape and volume still indefinite. ~ 21 ~

22 Phase changes occur as a substance's temperature (and KE) increase or decrease relative to that material's IMFs. This occurs without a change in identity and can be considered physical changes. Memorize the phase changes and their names: (s) (l) = fusion or "melting" (l) (s) = solidification or "freezing" (l) (g) = vaporization or "boiling" (g) (l) = condensation (g) (p) = ionization (p) (g) = recombination (Hint: make flashcards for these!) Ex.1) As a sample of zinc metal is heated in a crucible, which phase changes could potentially occur? ~ 22 ~

23 Ex.2) After exiting the tip of the flame from a burner and cooling to room temperature, the superheated carbon dioxide and water produced by combustion might undergo which phase changes? Ex.3) Which state(s) of matter have definite (unchanging) and indefinite (changing) shapes? Definite: Indefinite: Ex.4) Which state(s) of matter have definite volumes and which will expand to fill their containers? Definite: Expand: Ex.5) Compressibility measures how easily a substance can be compacted into a smaller volume. More space between particles = more compressibility. Rank the states by increasing compressibility: ~ 23 ~

24 The melting point (MP) and boiling point (BP) define the points at which a substance's KE either partially or fully overcomes its IMFs and can be used to predict states. Ex.6) Ice melts at 0 C and boils at 100 C. Predict the state a sample of water would be at each of the following temperatures: 25 C 184 C -14 C 99.9 C C C Ex.7) Helium's MP is C and BP = C. Predict helium's state at each of the following temps: -270 C -273 C -14 C 25 C ~ 24 ~

25 Ex.8) Copper metal melts at 1358 K and boils at 2835 K. Given a sample of copper at room temperature (298K), which phase change(s) will occur as it is heated to 1700 K in a crucible? Ex.9) How will the shape, volume, and compressibility of the copper sample change in example 8? Shape: Volume: Definite Definite Compressiblity: Virtually none Ex.10) In terms of IMFs, how is it possible to have solids, liquids, and gases all at the same temperature? ~ 25 ~

26 ~ 26 ~

Matter A Review. Has mass Takes up space. Chemistry is the study of MATTER!

Matter A Review. Has mass Takes up space. Chemistry is the study of MATTER! Matter A Review Has mass Takes up space ex. Chemistry is the study of MATTER! Topic 4.D - Classifying Unit 1 Organizing Matter 2011 Classifications of Matter Matter Anything that has mass and takes up