Chemistry

1. Chemistry

2. A Science for All Seasons • What is Chemistry? • The study of the composition of matter • The study of the changes matter undergoes • Why study Chemistry? • Chemistry touches all aspects of life • A basic understanding of chemistry will enable you to make informed and balanced decisions • Most importantly, to learn how to experiment and analyze data

3. Technological: Application of knowledge for practical purpose Has typically come before the scientific knowledge in the course of human history Fire, food preservation, dyes, medicines Philosophical: Science grew from this philosophical speculation of nature This led to Alchemy, which is the experimental root of chemistry Science and Technology: The Roots of Knowledge

4. Science and the Scientific Method • Reproducible and Reliable • Testable • Tentative • Predictive • Explanatory

5. Science • Hypothesis (educated guess): • Tentative • Testable • Explanatory • Based on an observation • Used to design experiments

6. Science • Theory: • Set of tested hypotheses • Explanatory • Tentative

7. Science • Law: • Summarize large amounts of data • Describe natural phenomena • Can be stated mathematically in most cases • DOES NOT EXPLAIN!!!

8. Science • Models: • Tangible items or pictures used to represent invisible processes

9. Limitations of Science • Science is limited to: • The study of OBSERVABLE processes • The study of natural processes in which variables can be controlled

10. Solving Society’s Problems: Scientific Research

11. Chemistry: A Study of Matter and Its Changes • Matter: Occupies space (i.e. has volume) and has mass • Mass: Amount of matter in a sample • Independent of location • Weight: A force that acts upon a mass • Gravity • Dependent upon location

12. WORKED EXAMPLE 1.2Mass and Weight On the planet Mercury, gravity is 0.376 times that on Earth. a. What would be the mass on Mercury of a person who has a mass of 62.5 kilograms (kg) on Earth? b. What would be the weight on Mercury of a person who weighs 124 pounds (lb) on Earth? Solution a. The person’s mass would be the same (62.5 kg) as on Earth; the quantity of matter has not changed. b. The person would weigh only 0.36  124lb = 46.6 lb; the force of attraction between planet and person is only 0.376 times that on Earth. Exercise 1.2A At the surface of Venus, the force of gravity is 0.903 times that on Earth’s surface. a. What would be the mass of a standard 1.00-kg object on Venus? b. A man who weighs 198 lb on Earth would weigh how much on the surface of Venus? Exercise 1.2B On the (liquid) surface of Jupiter, the force of gravity is 2.34 times that on Earth. a. What would be the mass of a 52.5-kg woman at that location on Jupiter? b. A man who weighs 212 lb on Earth would weigh how much on Jupiter?

13. Chemistry: Physical Properties • Properties that can be observed without changing the substance • Easily observed or measured • Using five senses BP, MP, color, physical state @ room temperature, odor, electrical conductivity, solubility, magnetism, density, taste, crystal form

14. Chemistry: Chemical Properties • Those properties of a substance that can only be studied by forming new substances, through a change in composition called a chemical reaction • Describes how something reacts with another substance • how a substance behaves in the presence of another substance • Flammability, reactivity with acid, pH, heat of combustion

15. Physical No change in basic nature or composition of substance Basically, a change in size, shape or state Substance has the same properties after the change Chemical Changes basic nature and composition of substance Substance has completely different properties after change Indicated by Formation of a solid (precipitate, ppt) Formation of a gas (bubbles)/odor Color change Energy change (release or absorption of heat, release of light, release of sound) Chemistry: Physical and Chemical Changes

16. WORKED EXAMPLE 1.3Chemical Change and Physical Change Which of the following events involve chemical changes and which involve physical changes? a. Your hair is cut. b. Lemon juice converts milk to curds and whey. c. Water boils. d. Water is broken down into hydrogen gas and oxygen gas. Solution We examine each change and determine whether there has been a change in composition or structure. In other words, we ask “Have new substances that are chemically different been created?” If so, the change is chemical; if not, it is physical. a. Physical change: The composition of the hair is not changed by cutting. b. Chemical change: The compositions of curds and whey are different from the composition of the milk. c. Physical change: Both the liquid water and the invisible water vapor formed when liquid water boils have the same composition; the water merely changes from a liquid to a gas. d. Chemical change: New substances, hydrogen and oxygen, are formed. Exercise 1.3A Which of the following events involve chemical changes and which involve physical changes? a. Gasoline vaporizes from an open container. b. A piece of magnesium metal burns in air to form a white powder called magnesium oxide. c. A dull knife is sharpened with a whetstone. Exercise 1.3B Which of the following events involve chemical changes and which involve physical changes? a. A steel wrench left out in the rain becomes rusty. b. A stick of butter melts. c. A wooden log is burned. d. A piece of wood is ground up into sawdust.

17. Classification of Matter Solid: Highly organized particles spaced closely together, vibrating but not moving Liquid: Disorganized particles spaced closely together, moving freely Gas: Disorganized particles spaced very far apart, moving freely

18. Classification of Matter

19. A pure substance will have A constant composition The same properties regardless of physical state and origin Elements and compounds are the only “pure” substances A mixture will have Changing properties based on its changing composition Mixtures can be solids (alloys), liquids or gases Mixtures can be separated into pure substances using easy, physical means Separability is the best test to classify mixtures vs. pure substances Matter: Substances and Mixtures Pure substances and mixtures are differentiated based on the constancy of composition

20. Elements Cannot be broken down into a simpler substance that has similar properties Shows no change after heating in a vacuum or be plied with electrical current Smallest particle is an atom Approximately 114 distinct elements Metals (84 elements that are shiny, malleable and conduct electricity) vs. nonmetals (22 elements that are brittle, nonconductive, and not lustrous) Compounds Can be broken down into a simpler substance, but only through a chemical reaction Formed when two or more atoms chemically combine in a simple, whole number ratio to form a new substance with new properties Smallest particle is either a molecule or a formula unit Law of definite composition: Basically, water will always consist of 11% hydrogen and 89% oxygen by weight, regardless of where it is formed Matter: Pure Substances

21. Matter: Chemical Language • Elements are usually represented by chemical symbols • A one or two letter abbreviation • First letter is capital, second is lower case • If there is more than one capital letter, the substance is a compound

22. WORKED EXAMPLE 1.4Elements and Compounds Which of the following represent elements and which represent compounds? C Ca HI BN In HBr Solution C, Ca, and In represent elements (each is a single symbol). HI, BN, and HBr are composed of two symbols each and represent compounds. Exercise 1.4A Which of the following represent elements and which represent compounds? He CuO No NO KI Os Exercise 1.4B How many different elements are represented in the entire list of Exercise 1.4A?

23. Homogeneous Constant composition Heterogeneous Variable composition Mixtures • Physical combinations of any two or more substances in no fixed proportion • Certain properties vary because of this changing composition • BP and FP • Can be separated by easy, physical means • A magnet, a filter, a sieve, boiling, dissolving

24. Matter: Homogeneous and Heterogeneous Mixtures

25. The Measurement of Matter • Système international d'unités (SI system) • The metric system! • Used worldwide • Based on powers of ten • Distinct advantages: • Simpler units • Simpler calculations

26. Powers of Ten

27. WORKED EXAMPLE 1.5Prefixes and Powers of Ten Convert each of the following measurements to a unit that replaces the power of ten by a prefix. a. 2.89  10–3 g b. 4.30  103 m Solution Our goal is to replace each power of ten with the appropriate prefix from Table 1.5. For example, 10–3 = 0.001, corresponding to milli(unit). (It doesn’t matter what the unit is; here we are dealing only with the prefixes.) a. 10–3 corresponds to the prefix milli-; 2.89 mg; that is, 10–3 (unit) = milli(unit). b.103corresponds to the prefix kilo-; 4.30 km; that is, 103 (unit) = kilo(unit). Exercise 1.5 Convert each of the following measurements to a unit that replaces the power of ten by a prefix. a. 7.24  103 g b. 4.29  10–6 m c. 7.91  10–3 s d. 2.29  10–2 g e. 7.90  106 m

28. Measurement: Units • Mass: Kilogram • Usually use grams or milligrams instead • Length: Meter • Usually use centimeters or millimeters instead • Derive area (Length * Length = meters2) • Derive volume (L * L * L = m3) • 1 m2 ≠ 100 cm2 • Time: Seconds • Temperature: Kelvins • Usually use Celsius

29. Measurement Practice • Without doing a detailed calculation, determine which of the following is a reasonable (a) mass and (b) height for a two year old child. • 10 mg, 85 mm • 10 g, 85 cm • 10kg, 850 cm • 100 g, 8.5 m • Without doing a detailed calculation, determine which of the following is a reasonable area for the front cover of your textbook. • 500 mm2 • 50 cm2 • 500 cm2 • 50 m2 • Without doing a detailed calculation, determine which of the following is a reasonable volume for your textbook. • 1600 mm3 • 16 cm3 • 1600 cm3 • 1.6 m3

30. Unit Conversions • Also called dimensional analysis • Any equality can be written as a fraction equal to 1 • Therefore, we will only change the units that we report in, not the magnitude • Common factors can be cross-canceled • If a unit appears in both a numerator and a denominator, it can be canceled out • The number is not canceled

31. Let’s Practice! • Write conversion factors for the following: • 1000 cm3 = 1000 mL • 1 kg = 1000 g • 1 kg = 2.2 lb • 1 L = 1000 mL • How many meters are in 76 cm? • How many milligrams are in 0.53 kg? • How many mL are in 0.439 L? • How many mols of Cu are in 10.0 g of Cu? • How many grams of Cu are in 1.5 mols of Cu?

32. Density • Density is a physical property • Characteristic for a substance • Can be used to identify a substance • How “thick” something is... • D = mass / volume • Units of g/cm3 for solids and g/mL for liquids • Something less dense will float on something more dense • Solving for • Mass • DV = m • Volume • V = m/D

33. Density of Common Substances

34. More Practice • What is the density of ethanol if the mass equals 79 grams and the volume equals 100. mL? • What is the density of olive oil if 21 mL weighs 19 g? • What is the mass of 3.0 mL of ether? Dether= 0.70 g/mL • What is the volume of 27.2 g of mercury? Dmercury= 13.3 g/mL • What volume (in mL) does 84 g of carbon tetrachloride occupy? DCCl4= 1.59 g/mL

35. Temperature • Measure of the amount of kinetic energy a substance has • It is NOT, no matter what your book says, a measure of how hot or cold a substance is • Relative • Kelvin • Base unit • Absolute zero • K = °C + 273 • °C = K - 273 • °C vs. °F • °C = 5/9(°F – 32) • °F = (9/5 * °C) + 32

36. Energy: Heat and Temperature • Energy is the ability to do work or cause change • Temperature indicates the tendency of heat energy to be transferred from hot to cold) • Calories (cal) ≠Calories (C) • Food calories are kilocalories • Joule (J) • SI unit of energy • 1 cal = 4.184 J -or- 1 kcal = 4.184 kJ

37. Practice Again! • A hamburger contains 409 kcal. Convert this to kJ. • A jogger burns 2200 kJ in a run. How many kcal is this? How many hamburgers would she need to eat to replace this? • A European woman on average consumes food with an energy content of 7525 kJ per day. What is her daily intake of kcal?

38. Homework • Homework questions are posted online!!! • Due at the beginning of class next Thursday. • Either insert answers into the document and print to submit *or* • Write the complete answers neatly on notebook paper.