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chapter 1 - CHEMISTRY 1211 PRINCIPLES PRINCIPLES OF...

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Unformatted text preview: CHEMISTRY 1211 PRINCIPLES PRINCIPLES OF CHEMISTRY I CHEMISTRY 1 CHAPTER 1 CHEMICAL FOUNDATIONS 2 1.1 Chemistry – What is it? • Chemistry is often described as a central science • Chemistry is the science that describes matter. (its properties, the changes it undergoes, and the energy changes that accompany those processes.) 3 macroscopic symbolic microscopic (Atoms and molecules) 4 SiO2 5 The Nature of The Matter Matter Matter is the material of the universe. It occupies 6 space and has mass. space CHEMISTRY:STUDY OF MATTER MATTER i ts structure and properties i ts transformation from one form to another 7 Atoms and Elements • Matter is composed of various types of atoms; • Atoms: The smallest particle of an element that maintains its chemical identity through all chemical and physical changes. • Element: a substance that cannot be decomposed into simpler substances by chemical means. 8 Atoms and Elements • One substance changes to another by recognizing the way the atoms are attached to another. 9 1.2 The Scientific Method Hypothesis Observation Observation Experiment to test the hypothesis A law summarizes what happens: a theory (model) is an attempt to law theory explain why it happens. e.g. the law of conservation of mass; Bohr’s quantum model, Einstein’s relativity. Einstein’s 10 1.3 UNITS OF MEASUREMENT UNITS • We make QUALITATIVE We QUALITATIVE observations of reactions — changes in color and physical state. color • We also make QUANTITATIVE We MEASUREMENTS, which involve MEASUREMENTS which numbers + units. numbers 11 1.3 UNITS OF MEASUREMENT UNITS Use SI units — based on the Use SI metric system metric English system 12 Write the units: In 1999, the $125 million Mars Climate Orbiter spacecraft was lost when it entered the Martian atmosphere 100 km lower than planned. The navigation error would have been avoided if people had labeled their units of measurement. Engineers who built the spacecraft calculated thrust in the English unit, pounds of force. Jet Propulsion Laboratory engineers thought they were receiving the information in the metric unit, newtons. 13 SI base units used in chemistry measurement unit symbol Mass Kilogram kg Length Meter m Temperature Kelvin K time Second s or sec Amount of substance Mole mol Electric current Ampere A Luminous intensity Candela cd 14 prefixes prefixes • 1 kilometer (km) = 1000 meters (m) • 100 cm 100 = 1m • 1000 mm = 1m • 106 µm = 1m • 109 nm =1m 15 VOLUME VOLUME TIME TIME 1000 mL = 1L 1 mL = 1cc = 1 cm3 60 s = 1min 60 min = 1hr 60 MASS 1 kg = 1000 g 1 mg = 0.001 g mg 16 Unit factor method 2.54 cm = 1 in 2.54 cm 2.54 Unit factor: Unit =1 Or 1 in 7.86 cm × 7.86 1 in in 2.54 cm 2.54 = 7.86 7.86 1 in in 2.54 cm 2.54 =1 in = 3.09 in 2.54 2.54 17 Mass and Weight • Mass: a measure of the resistance of an object to a change in its state of motion (F = ma). acceleration acceleration • Weight: a force exerted on a object by gravity on the earth (weight = mg). acceleration due to gravity acceleration • Mass ≠ weight 18 1.4 Every measurement has uncertainty Greater number of digits in the measurement, more certainty Figure 1.7 (1.9) 20.15 mL Certain digits; uncertain digits measuring device chosen: how much uncertainty we will accept 19 Uncertainty ? * Equipment, calibration * person making the measurement 20 Reading a measuring device: We always estimate the RIGHTMOST digit Uncertainty can be expressed with the ± sign Or assume an uncertainty of 1 unit in the rightmost digit 21 • • • • 4.24 cm 4.23 cm 4.28 cm 4.28 cm uncertain digit: estimated Certain digits 22 Graduated Graduated cylinder cylinder Buret 34 33 Beaker 40 40 30 30 32 20 20 31 33.15 10 +/- 0.01 mL 10 33.1 +/- 0.1 mL 33 +/- 23 1 mL Precision and accuracy: figure 1.8 (1.10) Precision: reproducibility random errors Accuracy: close to actual value systematic error If systematic errors are absent, we assume the average of a series of precise measurement is accurate (or close to the true value). Understand the sample exercise 1.2 on page 12 -13. 24 Absolute Uncertainty (Absolute Error) The absolute uncertainty (usually called absolute error) is the size of the range of values in which the "true value" of the measurement probably lies. If a measurement is given as 4.5 cm, the absolute uncertainty is 0.1 - 0.5 cm. (always 1-5 digits) Relative Uncertainty (Relative Error) Relative uncertainty is the ratio of the absolute uncertainty of a measurement to the best estimate. It expresses the relative size of the uncertainty of a measurement (its precision). 25 1.5 Determining which figures are significant Significant digits: digits that indicate the digits precision of measurements; digits of a precision measured number that have uncertainty only in the last digit. last 26 1.5 Determining which figures are significant • Rules: • 1. Non zero integers Leading zeros 2. Zeros Captive zeros Trailing zeros 3. Exact numbers 4. Mathematical operations 27 Significant figures and calculations • 0.01008 • Leading zeros • 1008 • Captive zeros • 1008.0 • Trailing zeros with and without a decimal point • 1000 28 EXPONENTIAL NOTATION & SIGNIFICANT FIGURES SIGNIFICANT 0.000 000 28 = ? 23.742 has ? significant figures 1 x 10 4 0.00000023 ? 1 x 10-4 =? =? 29 Calculations • Addition & subtraction • Multiplication & division 30 Multiplication & division • Addition and subtraction • Exponential notation: • 75,000000 = • 0.00635 = 31 Sig figs in calculations In a calculation keep track of sig figs Cannot have more sig figs in answer than in the original data Suppose you want to find the density of a new ceramic: You measure the mass on a balance: 3.8056 g and its volume is 2.5 mL Density will be : 1.5222 g/mL or 1.5 g/mL? 32 FACTOR LABEL METHOD or DIMENSIONAL ANALYSIS DIMENSIONAL A procedure in which the equations are set up so that all the unwanted units are cancel and only the desired units remain cancel 33 1.7 Calculations Using Temperature 1.7 T (K) = tt((°C) + 273.15 T (K) = °C) + 273.15 •• Body temp. = 37 °°C + 273 = 310 K Body temp. = 37 C + 273 = 310 K Body Body •• ooF = 9/5 ooC + 32 F = 9/5 C + 32 9/5 9/5 •• ooC=5/9 ((oF– 32) C= 5/9 oF – 32) 34 Temperature Scales Temperature Fahrenheit Boiling Point of water 212 180° Freezing Point of water Absolute zero 32 - 459o Celsius Kelvin 100 373.15 100° 0 - 273o 100° 273.15 0 35 1.8 DENSITYa fundamental property by which a particular kind of matter can be characterized and identified Density = mass per unit volume 36 D=M/V M=VD V=M/D Volume is typically in mL or cm3 ( 1mL = 1 cm 3 ) Mass is typically in grams. Density is typically in g/mL or g/cm 3 37 EFFECT OF TEMPERATURE ON DENSITY DENSITY D= M V Volume increases with temperature Volume and if mass remains constant, density must ? 38 Problem: A piece of copper has a mass Problem of 57.54 g. It is 9.36 cm long, 7.23 cm wide, and 0.95 mm thick. Calculate density (g/cm3). density 39 SOLUTION SOLUTION 1. Get dimensions in common units. convert 0.95 mm into cm : 1 cm = 10 mm Conversion factor : 1 cm/10 mm 0.95 mm x 1cm/10 mm = 0.095 cm 0.95 40 SOLUTION SOLUTION 2. Calculate volume in cubic centimeters. 9.36 cm x 7.23 cm x 0.095 cm = 6.4 cm3 6.4 3. Calculate the density : 3. Mass/volume = 57.54g/6.4 cm3 = 8.9906 g/cm3 57.54g/6.4 8. answer reported as = 9.0 g/cm3 answer 9.0 41 1.9 PROPERTIES OF MATTER MATTER CAN EXIST IN 3 STATES : MATTER SOLID, LIQUID, GAS SOLID, PHYSICAL CHEMICAL 42 What are some physical properties? properties? • color • melting and boiling point melting (physical state – solid, liquid, gas) liquid, • Odor • DENSITY 43 Physical Change: A physical change is a change in the physical form of a substance, not in its chemical composition. 44 Some physical changes physical would be would • boiling of a liquid • melting of a solid • dissolving a solid in a dissolving liquid to give a homogeneous mixture — a SOLUTION. SOLUTION 45 Chemical Properties Chemical Chemical properties of a substance are those that describe how the substance interacts with other substances to produce new substances 46 Chemical Changes Chemical A chemical change or chemical reaction involves the transformation of one or more atoms or molecules into one or more different molecules. Aluminum + Bromine Aluminum Bromide 47 In each case, decide if each underlined property is a physical or chemical property: a) The normal color of sulfur is yellow. b) Iron is transformed into rust in the presence of air and water. c) Dynamite can explode. d) The density of uranium metal is 19.06 g/mL. e) Aluminum metal melts at 933 K. f) Chlorophyll, a plant pigment, is green. g) Copper can be hammered into thin sheets 48 In each case, decide if the change is a chemical or physical change. a) A cup of household bleach changes the color of your favorite T-shirt from purple to pink. b) Water vapor in your breath condenses in the air on a cold day. c) Plants use carbon dioxide from the air to make sugar. d) Butter melts when placed in the sun. 49 Puzzle time: keep your brain active … If 2 * 3 = 10 7 * 2 = 63 6 * 5 = 66 8 * 4 = 96 ? Then: 9 * 7 = ???? Want to know the answer? I’ll let you know in recitation. 50 ...
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