Properties the characteristics that give each substance a unique identity

Transcription

1 All course materials, including lectures, class notes, quizzes, exams, handouts, presentations, and other materials provided to students for this course are protected intellectual property. As such, the unauthorized purchase or sale of these materials may result in disciplinary sanctions under the Campus Student Code. Chemistry the study of matter, the stuff of the universe Questions 1. What is stuff? 2. How much stuff? 3. Properties of stuff? 4. What does stuff do? 5. Why does stuff do that? Why is this course required? develop problem solving skills learn fundamental physical models of stuff gain technical perspective on current events appreciate life's little mysteries Properties the characteristics that give each substance a unique identity Intensive properties independent of the amount of substance present ex: color, melting pointdoes not alter the basic nature of substance Extensive properties varies with the quantity of the substance present ex: volume, mass Chemical Formulas Chemical formulas provide information about the ratios of the elements in molecular compounds but not how they are bonded. To communicate information about bonding and shape, arrangement of atoms can be represented in three other ways: Structural formulas Ball-and-stick model Space-filling model We are what we repeatedly do. Excellence, then, is not an act, but a habit. Aristotle Page 1 of 10

2 States/ Phases of Matter Physical Properties Can be determined without changing basic composition of substance ex- color, Tb, Tf, density Physical Change/ Reaction Does not alter the basic nature of substance Chemical Properties Can only be observed over the course of a chemical reaction ex- flammability, corrosiveness Chemical change/ reaction alters the basic nature of substance Bond breaking and bond making Concept test; Chemical or physical processes? We are what we repeatedly do. Excellence, then, is not an act, but a habit. Aristotle Page 2 of 10

3 The Scientific Method a systematic procedure for solving problems and exploring natural phenomena Observations (data) Data can be qualitative or quantitative Data collected under controlled conditions (experiments) These experiments must be repeatable and reproducible Hypotheses tentative explanations designed to guide experimentation must be testable and falsifiable (can be proven false) must be rejected or corrected when they conflict with experiment Karl Popper a scientific hypothesis/ theory must be falsifiable (capable of being proven false) Example hypothesis: All swans are white. Testing of the hypothesis is searching for a non-white swan not counting white swans If we find one single non-white swan we conclude that the hypothesis is false Science thus strives for falsification of hypotheses not proving them true Theories A well-tested explanation for experimental data based on a set of hypotheses. Must be discarded or refined when they can't explain new experimental results A good theory... Explains currently available data Is as simple as possible Accurately predicts results of future experiments Suggests new lines of work and new ways to think Measurements quantitative observations, estimations Measurement always involves some uncertainty Reliability of measurement depends on measuring device and skill of operator Read between the lines estimate between divisions is expressed via significant figures We are what we repeatedly do. Excellence, then, is not an act, but a habit. Aristotle Page 3 of 10

4 Measure the temperature a. 28 o C b. 29 o C c o C d o C Measure the bug a. 1 inch b. 2 inch c. 1.6 inch d inch Which of the following most correctly expresses volume of the liquid in the buret below? a. 2.6 ml b ml c. 1.4 ml d ml Accuracy closeness to the true value Precision closeness of multiple measurements to each other Exact numbers are for some reason exactly known they can be obtained either by counting or by definition Exact numbers do not affect significant digits in a calculation by definition There are exactly 12 inches in 1 foot There are 7 days in one week by counting There are 4 people in the room Our cat had 6 kittens The motor has 6 cylinders We are what we repeatedly do. Excellence, then, is not an act, but a habit. Aristotle Page 4 of 10

5 Are units important? Exponential Form of Numbers/ Scientific Notation very large and very small numbers can be written in a convenient form that shows the size or amount of a number as well as the number of significant figures 1200 can be written as can be written as A number expressed in scientific notation has two parts 1. The coefficient number from 1 up to but not including The exponent the power of 10 the coefficient is multiplied by Numbers larger than 1 have positive exponents Numbers smaller than 1 have negative exponents The exponent is indicates the number of places the decimal point has to be moved Complete the following table Scientific notation Decimal notation Number Exponential meaning 1,000, one million 100, one hundred thousand 10, ten thousand 1, one thousand one hundred / / / /1000 We are what we repeatedly do. Excellence, then, is not an act, but a habit. Aristotle Page 5 of 10

6 Significant Figures (sig figs, sf) all digits that are known for certain plus one uncertain digit The last digit in a reported measurement is estimated, read between the lines The number of significant figures in a measurement largely depends on the measuring device In general, the greater the number of sig figs, the more precise and reproducible the measurement Significant figure rules 1. Any digit that is not zero is significant. 2. Captive/buried zeros zeros between nonzero numbers are significant. 3. Leading zeros zeros at the beginning of a number with a decimal point are not significant 4. Trailing zeros Zeros at the end of a number with a decimal point are significant Zeros at the end of a number w/o a decimal point are ambiguous; use scientific notation Rules for Significant Figures in Calculations The quality of a calculation result is limited by the worst measurement used in the calculation For multiplication and division The answer contains the same number of sig figs as there are in the measurement with the fewest sig figs For addition and subtraction The answer must be rounded to the first uncertain decimal place Rounding We will use simple rounding in this course If the first digit to be discarded is 5 or greater, add 1 to the last sig fig otherwise leave it alone NEVER round until you get a final answer. Report the result of the following calculations involving measured numbers s 8 m 39.37in m = = = We are what we repeatedly do. Excellence, then, is not an act, but a habit. Aristotle Page 6 of 10

7 Conversion factors/ Basic strategy for unit conversion A conversion factor has equivalent quantities in both numerator For example, one mile is defined as 5280 feet 5280feet mile = 1 = 1 mile 5280 feet Multiplying by a conversion factor only changes units The result is equivalent to the original measurement Often, unit conversion problems will require several conversion factors What is the speed of light in furlongs per fortnight? c = m/s 1 furlong = m 1 fortnight = 14 days Metric system Scientists and engineers use the metric system for measurement Metric unit English (or Imperial) unit Length Meter, m Feet, ft Volume Liter, L Quart, qt Mass Gram, g Ounce, oz furlongs/fortnight The metric system is a measurement system based on powers of 10 Easier calcs leading to fewer mistakes and less confusion Increases the chance that scientific principles and concepts can be understood Know how to do conversion between units containing all the following prefixes prefix symbol multiplier prefix symbol multiplier Tera T deci d Giga G centi c Mega M milli m kilo k micro µ Convert cm to meters nano n pico p We are what we repeatedly do. Excellence, then, is not an act, but a habit. Aristotle Page 7 of 10

8 Convert micrograms to kilograms Express 2548 m in each of the following units: km, mm, cm, and µm Density the mass of a substance per unit volume, density = mass volume characteristic physical property of matter (varies from substance to substance) can be used to help identify a substance typical units grams per cubic centimeter (g/cm 3, or equivalently g/ml) for liquids and solids grams per liter (g/l) for gases A student wonders whether a piece of jewelry is made of pure silver. She determines that its mass is 3.17 g. She measures its volume by water displacement in a graduated cylinder determines that its volume is 0.3 ml. Could the jewelry be made of pure silver? (density of Ag is g/cm 3 ) density can be used as a conversion factor in calculations the density of olive oil is g/cm 3, from this two conversion factors can be written 0.92 g cm 3 = 1 and = 1 note cm 3 = ml (exact, set by definition) 3 cm 0.92 g We are what we repeatedly do. Excellence, then, is not an act, but a habit. Aristotle Page 8 of 10

9 Olive oil has a density of 0.92 g/ml. How many ml of olive oil would you measure out if you needed 38 grams of olive oil? What is the mass of ethyl alcohol that fills a 225 ml container? The density of ethyl alcohol is is g/ml. Temperature Scales What is temperature? It is hard to define. One way: conditions under which certain transitions occur Gabriel Fahrenheit (1714, German physicist) Zero degrees was lowest temp achievable in his lab Set scale so that 180 degrees separated Tb and Tf of water Anders Celcius (1742, Swedish astronomer) Created the Centigrade scale Zero degrees was set at the freezing point of water Set scale so that 100 degrees separated Tb and Tf of water William Thompson, Baron Kelvin (1848) Proposed temp as measure of average molecular speed Zero Kelvin is theoretical temp at which all motion stops Absolute zero calculated to be degrees below 0 o C We are what we repeatedly do. Excellence, then, is not an act, but a habit. Aristotle Page 9 of 10

10 = C + 32 K = C F 5 9 Only Centigrade and Kelvin scales are used in the study of chemistry. The average outside temperature in New York City during January is 37.9 o F. Convert this temperature to degrees Celsius. 3.3 o C Significant figures for temperature conversion use the same number of decimal places as was in the original temperature We are what we repeatedly do. Excellence, then, is not an act, but a habit. Aristotle Page 10 of 10