Chapter 1: Science and Measurements Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. © 2014 John Wiley & Sons, Inc. All rights reserved. 1.1 Scientific Method Objectives • Explain the terms: law, hypothesis, experiment, and theory © 2014 John Wiley & Sons, Inc. All rights reserved. 1.1 Scientific Method Science is broken into various disciplines • Chemistry involves the study of matter and its changes • Knowledge important in many other disciplines like biology, health sciences, and geology Matter © 2014 John Wiley & Sons, Inc. All rights reserved. 1.2 Matter and Energy Objectives • Define matter and energy • Describe three states of matter and two forms of energy • Describe physical properties and physical change • Be able to provide examples of each © 2014 John Wiley & Sons, Inc. All rights reserved. 1.2 Matter and Energy Matter described in terms of physical properties • characteristics that can be determined without changing what it is made of (chemical composition) • Melting and boiling points • Color • Physical State • Odor © 2014 John Wiley & Sons, Inc. All rights reserved. 1.2 Matter and Energy Matter is generally found in one of three physical states or phases 1. Solid • Have fixed shapes and volumes 2. Liquid • Have variable shapes and fixed volumes 3. Gas • Have variable shapes and volumes © 2014 John Wiley & Sons, Inc. All rights reserved. 1.2 Matter and Energy What causes different phases? • Interactions between particles (atoms, molecules, ions) © 2014 John Wiley & Sons, Inc. All rights reserved. 1.2 Matter and Energy Work has been done any time matter is changed • Involves energy • ability to do work and to transfer heat Energy is found in two forms 1. Potential energy • Stored energy • For example: water behind a dam 2. Kinetic energy • Energy of motion • For example: water flowing through the dam © 2014 John Wiley & Sons, Inc. All rights reserved. 1.2 Properties of Matter Property • Two General Types: Physical • Characteristic of a substance that can be observed without changing the basic identity of the substance. Chemical • • • Characteristic of a substance that describes the way the substance undergoes or resists change to form a new substance. Most often the changes result from the reaction of a substance with one or more other substances. Sometimes energy (like heat or light) can trigger a change (decomposition). © 2014 John Wiley & Sons, Inc. All rights reserved. • 1.2 Classification of Matter • Pure substance – a single kind of matter that cannot be separated into other kinds of matter by any physical means. Element – a pure substance that cannot be • broken down into simpler pure substances by chemical means such as a chemical reaction, an electric current, heat, or a beam of light. Compound – a pure substance that can be broken down into two or more simpler pure substances by chemical means. • Mixture – a physical combination of two or more pure substances in which each substance retains its own chemical identity. Homogeneous Mixture: Heterogeneous Mixture: © 2014 John Wiley & Sons, Inc. All rights reserved. © 2014 John Wiley & Sons, Inc. All rights reserved. © 2014 John Wiley & Sons, Inc. All rights reserved. 1.3 Units of Measurement Objectives • Identify metric, English, and SI units © 2014 John Wiley & Sons, Inc. All rights reserved. 1.3 Units of Measurement Metric system is used most often worldwide Use the English units in the United States SI units are also used at times • International system of units related to the metric system © 2014 John Wiley & Sons, Inc. All rights reserved. 1.3 Units of Measurement © 2014 John Wiley & Sons, Inc. All rights reserved. 1.3 Units of Measurement Mass is the measure of the amount of matter in a sample • Most often measured in kilogram (kg) and gram (g) • 1 kg = 1000 g = 2.205 lb © 2014 John Wiley & Sons, Inc. All rights reserved. 1.3 Units of Measurement Metric Length Units • Meter (m): Base unit of length • Length is measured by determining the distance between two points Metric Volume Units • Liter (L): Base unit of volume • Volume is measured by determining the amount of space occupied by a threedimensional object 3 1 liter = 1000 cm 1mL = 1 cm3 – mL - Used for volume of liquids and gases 2014 John Wileyof & Sons, Inc. All rights reserved. – cm3 - Used for©volume solids Figure Comparison of the Base Metric System Units with Common Objects © 2014 John Wiley & Sons, Inc. All rights reserved. 1.4 Scientific Notation, SI and Metric Prefixes © 2014 John Wiley & Sons, Inc. All rights reserved. 1.3 Units of Measurement © 2014 John Wiley & Sons, Inc. All rights reserved. 1.3 Units of Measurement Figure - The Three Major Temperature Scales Converting Between Scales K = o C + 273 o C = K - 273 5 o C = F - 32 9 9 o o F = C + 32 5 o © 2014 John Wiley & Sons, Inc. All rights reserved. 1.3 Units of Measurement Unit of measure for energy is the calorie (cal) in metric and English systems One calorie is the amount of energy required to raise the temperature of 1 g of water by 1 °C. © 2014 John Wiley & Sons, Inc. All rights reserved. © 2014 John Wiley & Sons, Inc. All rights reserved. 1.4-1.5 Scientific Notation, SI and Metric Prefixes Objectives • Express values in scientific notation © 2014 John Wiley & Sons, Inc. All rights reserved. Exact Number • A number whose value has no uncertainty associated with it • Found in: – Definitions - 12 objects in a dozen – Counting - 15 pretzels in a bowl – Simple fractions - ½ or ¾ Inexact Number • A number whose value has a degree of uncertainty associated with it • Results any time a measurement is made © 2014 John Wiley & Sons, Inc. All rights reserved. 1.5 Measurements and Significant Figures Accuracy is related to how close a measured value is to a true value Precision is a measure of reproducibility © 2014 John Wiley & Sons, Inc. All rights reserved. Uncertainty in Measurements • A digit that must be estimated is called uncertain – A measurement always has some degree of uncertainty • Record the certain digits and the first uncertain digit (the estimated number) Figure - Scale on a Measuring Device • Measurements made with ruler A will have greater uncertainty than those made with ruler B © 2014 John Wiley & Sons, Inc. All rights reserved. 1.5 Measurements and Significant Figures Quality of equipment is one factor used in determining how precise and accurate a measurement is © 2014 John Wiley & Sons, Inc. All rights reserved. 1.5 Measurements and Significant Figures Significant Figures digits in a measurement that are reproducible when the measurement is repeated. Plus the first uncertain digit • You measure the mass of a quarter on a balance that produces readings with 0.1 g • The mass reads 5.7 g. The 7 is uncertain © 2014 John Wiley & Sons, Inc. All rights reserved. 1.5 Guidelines for Determining Significant Figures 1. 2. In any measurement, all nonzero digits are significant Example: 3456 has 4 sig figs Classes of zeros include: a. Leading zeros, at the beginning of a number, do not count as significant figures Example: 0.048 has 2 sig figs b. Confined zeros, between nonzero digits, are always counted as significant figures Example - 16.07 has 4 sig figs c. Trailing zeros, zeros at the right end of the number, are significant only if the number contains a decimal point Example - 9.300 has 4 sig figs d. Trailing zeros, zeros at the right end of the number, are not significant if the number lacks an explicitly shown decimal point Example - 150 has 2 sig figs © 2014 John Wiley & Sons, Inc. All rights reserved. 1.5 Guidelines for Determining Significant Figures Rounding Off Numbers • Process of deleting unwanted (nonsignificant) digits from calculated numbers 1. If the first digit to be deleted is 4 or less, drop it and all the following digits Example: 3.724567 becomes 3.72 (for 3 sig figs) 2. If the first digit to be deleted is 5 or greater, that digit and all that follow are dropped, and the last retained digit is increased by one Example: 5.00673 becomes 5.01 (for 3 sig figs) 1.5 Guidelines for Determining Significant Figures Scientific Notation • A numerical system in which numbers are expressed in the form A × 10n – A is the coefficient, the number with a single nonzero digit to the left of the decimal place – n is a whole number Coefficient Exponent 1.07 × 104 Multiplication sign Exponential term 1.5 Scientific Notation, SI and Metric Prefixes Converting from Decimal to Scientific Notation 1. The decimal point in the decimal number is moved to the position to the right of the first nonzero digit 2. The exponent for the exponential term is equal to the number of places the decimal point has moved – Examples 0.004890 = 4.890 × 10–3 (four sig figs) © 2014 John Wiley & Sons, Inc. All rights reserved. 1.5 Scientific Notation, SI and Metric Prefixes Multiplication and Division in Scientific Notation 1. To multiply exponential terms, add the exponents 2. To divide exponential terms, subtract the exponents © 2014 John Wiley & Sons, Inc. All rights reserved. 1.5 Scientific Notation, SI and Metric Prefixes • For numbers larger than 10, shift the decimal point to the left until you get a number between 1 and 10 • 505000 = 5.05 x 105 • For numbers smaller than 10, shift the decimal point to the right. The exponent will be negative • 0.000000505 = 5.05 x 10-7 © 2014 John Wiley & Sons, Inc. All rights reserved. 1.5 Measurements and Significant Figures Calculations with measured values should never change the degree of uncertainty in a value Multiplication and Division 1. The answer should have the same number of significant figures as the quantity with the fewest Four significant figures Three significant figures 6.038 × 2.57 = 15.51766 calculator answer = 15.5 correct answer Three significant figures © 2014 John Wiley & Sons, Inc. All rights reserved. 1.5 Measurements and Significant Figures Addition and Subtraction 2. In addition and subtraction, the answer has no more digits to the right of the decimal point than are found in the measurement with the fewest digits to the right of the decimal point 9.333 + 1.4 10.733 10.7 Uncertain digit (thousandths) Uncertain digit (tenths) (calculator answer) (correct answer) Uncertain digit (tenths) © 2014 John Wiley & Sons, Inc. All rights reserved. 1.5 Measurements and Significant Figures When dropping digits of an answer to report the value with the correct number of significant figures, rounding must occur • If the first digit dropped is 0 to 4, the last reported digit does not change • If the first digit dropped is 5 to 9, the last reported digit is increased by 1 © 2014 John Wiley & Sons, Inc. All rights reserved. A calculator gives an answer of 8.8274 when you multiply 4.60 by 1.919. In which of the following is the answer rounded to the correct number of significant figures? a.8.83 b.8.82 c.8.829 d.8.8 © 2014 John Wiley & Sons, Inc. All rights reserved.