It's a HIDDEN REALITY!

Transcription

1 It's a HIDDEN REALITY! hot aqueous extract of stimulating alkaloid fertilizer-grown, pesticide-treated fruit nutrient-enriched, spoilage-delayed carbohydrate flakes mixed in a white emulsion of fats, proteins and monosaccharides Truth is the shattered mirror strewn in myriad bits while each believes his little bit the whole to own Robert Burton Chapter 1: Keys to the Study of Chemistry 1.1 Fundamental Definitions Chemistry: the study of matter and its properties, the changes that matter undergoes and the energy associated with those changes The Properties of Matter Matter has properties: the characteristics that give each substance its unique identity Matter: the "stuff" of the universe: air, glass, planets, students ANYTHING THAT HAS MASS AND VOLUME PHYSICAL characteristics a substance shows by itself, without changing or interacting with another substance Chemists want to know the COMPOSITION of matter Alters its physical properties, NOT its composition Types and amounts of simpler substances that make it up A type of matter that has a defined, fixed composition CHEMICAL Characteristics a substance shows as it changes into or interacts with another substance (or substances) - tarnishing silver - rusting on a car - flammability CHEMICAL CHANGE: different stuff before and after

2 Physical A B A Chemical B particles have the same composition as A, but their arrangement is different Physical or chemical changes? particles have a different composition C C THE STATES OF MATTER Macroscopic view: Matter occurs in 3 physical forms called states: Solid: fixed shape that does not conform to container shape not defined by rigidity or hardness Liquid: varying shape; conforms to shape of container has an upper surface Gas: varying shape that conforms to shape of container fills entire container/no upper surface Atomic view: Solid: particles have a regular, 3D array Liquid: particles lie close together but move randomly around each other Gas: particles have very large distances between them and move randomly through the container

3 Temperature and Changes of State physical change caused by heating can generally be reversed by cooling MAIN THEME OF CHEMISTRY: We study observable changes in matter to understand their unobservable causes. This is NOT generally true for a chemical change. a) frost on your car window b) cornstalk growing from seed c) perspiration evaporates from your skin d) silver fork tarnishing e) gasoline fumes igniting from a spark macroscopic level atomic level The Importance of Energy in the Study of Matter Energy: the ability to do work all work involves moving something The TOTAL ENERGY an object possesses is the sum of its potential energy and its kinetic energy. pg 9: energy due to motion of object energy due to position of object Fuel vs. exhaust * When energy is converted from one form to another, it is conserved, not destroyed. * Situations of lower energy are more stable and favored over situations of higher energy.

4 1.2 CHEMICAL ARTS AND THE ORIGINS OF MODERN CHEMISTRY MEDICINE ALCHEMY ALCHEMY * an occult study that began in 1 AD and dominated thinking for over 1500 years * strived to change "baser" metals (like lead) into "purer" ones (gold) * The sense of "magic" was hard to correct * Their greatest contribution was in their technical methods: distillation, percolation, extraction and in their observation and experimentation (Greeks explained things soley by reason.) TECHNOLOGY MEDICINE TECHNOLOGICAL TRADITION During the Middle Ages and Renaissance, books were published with techniques to: * purify, assay and coin silver and gold * how to use a balance, crucible, furnace * how to make gunpowder and glass Quantitative measurement was introduced. * Alchemists influenced doctors during medieval times. * 1200's: distillates and extracts of roots and herbs for medicine * Paracelsus ( ): considered the body to be a chemical system illness was an imbalance that could be restored by treatment with drugs What is missing: Why things occur and how to predict behavior.

5 PHLOGISTON: an undetectable substance (fire element) that is released when things burn. Charcoal -- a lot of phlogiston Metals: not much at all Why do things stop burning in a closed vessel and seemingly weigh less? Heating metals forms "calx" and gain mass. Why? science/2011/06/01/acknowledging madame lavoisier/ Antoine Lavoisier: ( ) Discovered oxygen (normal component of air) combines with substances when burned. When oxygen runs out, things stop burning. Metal calxes (metal oxides) weigh more because they gain oxygen. QUANTITATIVE, REPRODUCIBLE MEASUREMENTS! 1.3 THE SCIENTIFIC APPROACH: DEVELOPING A MODEL We use quantitative theories to understand materials, make better use of them and to create new ones. THE SCIENTIFIC METHOD Observations Hypothesis Experiment Model (Theory) Further Experiments Hypothesis: tentative proposal that explains observations Must be testable by experiment Can be altered Experiment: A set of procedural steps that tests a hypothesis Contains at least 2 variables: quantities that can have more than 1 value Controlled: measures one variable while the others are intact MUST be reproducible. Model/Theories: set of conceptual assumptions that explains data from accumulated experiments Predicts related phenomena OBSERVATIONS *facts our ideas must explain *Quantitative information (data) is most useful because the numbers can reveal trends * Natural Law: when the same observation is made by many scientists in many situations with no clear exceptions ex: Law of Mass Conservation

6 1.4 CHEMICAL PROBLEM SOLVING Units and Conversion Factors All measurements have a NUMBER and a UNIT 1.4 cm A car traveling 350 miles in 7 hours has an average speed of 350 mi = 50 mi 7h 1h = 50 mi. h -1 CONVERSION FACTORS * ratios used to express a quantity in different units * equivalent quantities * even though the number and unit change after using conversion factors, the actual size of the quantity remains the same. * the conversion factor you choose must cancel all units except those you want in the answer. Using conversion factors is called the FACTOR-LABEL METHOD or DIMENSIONAL ANALYSIS

7 Using factor-label, convert 150 miles to feet. 1 mile = 5280 feet A systematic Approach to Solving Chemistry Problems 1. Problem Contains all the information needed. 2. Plan * identify the known and the unknown * think of steps to get you from the known to the unknown, i.e. formulas, conversion factors, constants * use a road map or flow diagram to get from known to unknown. * draw a picture of the problem -- it sometimes helps A LOT! 3. Solution Show calculations 4. Check Does your solution make sense? 5. Comment Is there an easier way to the problem? Are there any mistakes to avoid? Overview 6. Follow-up Problem Practice! 1.5 MEASUREMENT IN SCIENTIFIC STUDY Measuring for trade, building and surveying began thousands of years ago. The standards of measuring could vary. ex: 1 yard = tip of the king's nose to his fingertips 1790 France: metric system developed France: revised metric system: SI units = Systeme International d'unites Based on 7 fundamental units or base units identified by a physical quantity.

8 Derived units: combinations of the seven base units. example: VOLUME Scientific Notation: Convert 325 µl into cm 3 p18 has some nice metric-english conversion factors Convert 500 cm 3 into nm 3 LENGTH * 1/10,000,000 the distance between the equator and North Pole * 1,650, wavelengths of orange-red light from Krypton atoms * 1 m is the distance light travels in a vacuum in 1/299,792,458 s Biological cells micrometers MASS the quantity of matter in an object The standard is a platinum-iridium cylinder. Mass vs Weight Atomic scale pm and nm Atomic diameters Proteins 0.2 nm diameters of ~ 2 nm a constant a variable that depends on gravitational field Angstrom Mass is measured with a balance. An electronic balance creates an electric field that counteracts the local gravitational field. The current needed to restore the pan to zero is converted to the equivalent mass and displayed. o 1 A = m = 0.1 nm = 100 pm

9 DENSITY MASS VOLUME TEMPERATURE vs HEAT Because volume can change with temperature, density changes. ex. Water At a given temperature and pressure, the density of a substance is a characteristic physical property and has a specific value. A measure of how hot or cold one object is relative to another. Degree size is the same. The energy that flows from the object with the higher temperature to the object with the lower temperature. 1 degree C > 1 degree F Notice the different zero points. Kelvin temperatures are always positive. Kelvin has no degree sign. Conversions: K = o C o C = K o F = 9/5 o C + 32 o C = 5/9( o F - 32) TIME The atomic clock measures the oscillations of microwave radiation absorbed by gaseous cesium atoms cooled to 10-6 K 1 s = 9,192,631,770 oscillations! Scientists use lasers to measure reactions that occur in a few ps or fs NIST F1, the nation's primary time and frequency standard, is a cesium fountain atomic clock developed at the NIST laboratories in Boulder, Colorado. NIST F1 contributes to the international group of atomic clocks that define Coordinated Universal Time (UTC), the official world time. Because NIST F1 is among the most accurate clocks in the world, it makes UTC more accurate than ever before.

10 Extensive and Intensive Physical Properties 1.6 UNCERTAINTY IN MEASUREMENT: SIGNIFICANT FIGURES All measuring devices are made to limiting specifications. We use our imperfect senses and skills to read them. Therefore, EVERY measurement has some uncertainty. Depend on the amount of substance mass volume heat Independent of the amount of substance density temperature We always estimate the rightmost digit. Look at the calibrations and estimate between the marks. More digits = more certainty How to look at a measurement and tell how many significant figures there are: All nonzero digits are significant. Trapped zeros are significant. Trailing zeros are only significant if a decimal point is present. Leading zeros are never significant. attorneys should know about significantdigits and figures/

11 When doing calculations, we don't want to have more certainty in our answer than in our data. We have to round off the answer to reflect the data. The least certain measurement sets the limit on certainty for the entire calculation and determines the number of significant digits in the final answer. ROUNDING Look at the number to the right next to your last measured number: * greater than 5 rounds up 17.8 rounds to Multiplication and division The answer contains the SAME number of sig. digits as there are in the measurement with the fewest significant digits. 2. Addition and subtraction The answer has the same number of decimal places as there are in the measurement with the fewest decimal places. * less than 5 stays the same * if it is 5, odd rounds up and even stays the same rounds to 18 but 16.5 rounds down to rounds to 17 Always carry one or two extra digits throughout multi-step calculations and save rounding 'til the end. EXACT NUMBERS conversion factors counting numbers have no uncertainty Exact numbers do not limit the number of significant figures in a calculation.

12 PRECISION VS ACCURACY * reproducibility * how close the measurements in a series are to each other *how close each measurement is to the actual value Systematic error: your data will all be consistently too high or too low caused by the experimental system -- either a faulty device or a consistent mistake when taking a reading * can be taken into account through CALIBRATION: comparing the measuring device with a known standard.p Random error: when systematic error is absent, it produces values that are higher and lower than the actual value. * size depends on the measurer's skill and instrument's precision Precise measurements have low random error. Accurate measurements have low systematic error and usually a low random error. Sources of scientific information: frequency standards.cfm