Chapter to 1.5 Chemical Foundations

Chapter 1 Table of Contents Return to TOC Copyright © Cengage Learning. All rights reserved 1.1 Chemistry: An Overvie1.1 Chemistry: An Overview 1.2 The Scientific Metho1.2 The Scientific Method 1.3 Units of Measuremen1.3 Units of Measurement 1.4 Uncertainty in Measuremen1.4 Uncertainty in Measurement 1.5 Significant Figures and Calculation1.5 Significant Figures and Calculations

Measurement and Significant Figures

4 Chapter One Hall © 2005 Prentice Hall © 2005 General Chemistry 4 th edition, Hill, Petrucci, McCreary, Perry Getting Started: Some Key Terms Chemistry is the study of the composition, structure, and properties of matter and of changes that occur in matter. Matter is anything that has mass and occupies space. –Matter is the stuff that things are made of.

Section 1.1 Chemistry: An Overview Return to TOC Copyright © Cengage Learning. All rights reserved A main challenge of chemistry is to understand the connection between the macroscopic world that we experience and the microscopic world of atoms and molecules. You must learn to think on the atomic level.

Section 1.1 Chemistry: An Overview Return to TOC Copyright © Cengage Learning. All rights reserved Atoms vs. Molecules - Fundamental Principle #1 Matter is composed of tiny particles called atoms. Atom: smallest part of an element that is still that element. Molecule: Two or more atoms joined and acting as a unit.

7 Chapter One Hall © 2005 Prentice Hall © 2005 General Chemistry 4 th edition, Hill, Petrucci, McCreary, Perry Key Terms Molecules are larger units in which two or more atoms are joined together. –Examples: Water consists of molecules, each having two atoms of hydrogen and one of oxygen. –Oxygen gas consists of molecules, each having two atoms of oxygen. Water molecule Oxygen molecule

Section 1.1 Chemistry: An Overview Return to TOC Copyright © Cengage Learning. All rights reserved Oxygen and Hydrogen Molecules Use subscripts when more than one atom is in the molecule.

Section 1.1 Chemistry: An Overview Return to TOC Copyright © Cengage Learning. All rights reserved A Chemical Reaction - Fundamental Principle #2 One substance changes to another by reorganizing the way the atoms are attached to each other.

10 Chapter One Hall © 2005 Prentice Hall © 2005 General Chemistry 4 th edition, Hill, Petrucci, McCreary, Perry Key Terms Composition – the types of atoms and their relative proportions in a sample of matter. The composition of water is two parts (by atoms) of hydrogen to one part (by atoms) of oxygen. The composition of water is 11.2% hydrogen by mass, 88.8% oxygen by mass. –(Why the difference? Because hydrogen atoms and oxygen atoms don’t have the same mass!) –More on mass composition in section 3.5

Section 1.2 The Scientific Method Return to TOC Copyright © Cengage Learning. All rights reserved Science is a framework for gaining and organizing knowledge. Science is a plan of action — a procedure for processing and understanding certain types of information. Scientists are always challenging our current beliefs about science, asking questions, and experimenting to gain new knowledge. –Scientific method is needed. Science

Section 1.2 The Scientific Method Return to TOC Copyright © Cengage Learning. All rights reserved Steps of the Scientific Method Process that lies at the center of scientific inquiry.

Steps in the Scientific Method 1. Observations -quantitative - numerical data (5 g) - qualitative - descriptive data (blue) 2.Formulating hypotheses - possible explanation for the observation 3.Performing experiments - gathering new information to decide whether the hypothesis is valid whether the hypothesis is valid

Section 1.2 The Scientific Method Return to TOC Copyright © Cengage Learning. All rights reserved Scientific Models Summarizes what happens. Law Theory (Model) An attempt to explain why it happens. Set of tested hypotheses that gives an overall explanation of some natural phenomenon. Hypothesis A possible explanation for an observation.

Outcomes Over the Long-Term Theory (Model) - A set of tested hypotheses that give an overall explanation of some natural phenomenon. Natural Law - The same observation applies to many different systems

Scientific method. l Theories have predictive value. l The true test of a theory is if it can predict new behaviors. l If the prediction is wrong, the theory must be changed. l Theory- why l Law – how l Law – equation of how things change

Law vs. Theory A law summarizes what happens A theory (model) is an attempt to explain why it happens. Einstein's theory of gravity describes gravitational forces in terms of the curvature of spacetime caused by the presence of mass

Nature of Measurement Part 1 - number Part 1 - number Part 2 - scale (unit) Examples: 20 grams 6.63 x Joule·seconds A measurement is a quantitative observation consisting of 2 parts:

The Fundamental SI Units (le Système International, SI)

SI Units

Celsius & Kelvin

SI Prefixes Common to Chemistry PrefixUnit Abbr.Exponent MegaM10 6 Kilok10 3 Decid10 -1 Centic10 -2 Millim10 -3 Micro  Nanon10 -9 Picop10 -12

Section 1.3 Units of Measurement Return to TOC Copyright © Cengage Learning. All rights reserved Prefixes Used in the SI System

24 Chapter One Hall © 2005 Prentice Hall © 2005 General Chemistry 4 th edition, Hill, Petrucci, McCreary, Perry Volume The derived unit of volume (space taken up by an object) is the cubic meter (m 3 ). A very common unit of volume, not SI but still used, is the liter (L). The milliliter (mL; L) is also used, as is the cubic centimeter (cm 3 ). 1 mL = 1 cm 3. There are about five mL in one teaspoon.

Deriving the Liter l Liter is defined as the volume of 1 dm 3 l gram is the mass of 1 cm 3

Mass and Weight l Mass is measure of resistance to change in motion l Weight is force of gravity. l Sometimes used interchangeably l Mass can’t change, weight can

27 Chapter One Hall © 2005 Prentice Hall © 2005 General Chemistry 4 th edition, Hill, Petrucci, McCreary, Perry Mass and Time Mass is the quantity of matter in an object; weight is a force. The base unit of mass is the kilogram (kg; 1000 g); it already has a prefix. A 1-L bottle of soft drink weighs about a kilogram. Commonly used mass units include the gram and the milligram (mg; g). The SI base unit of time is the second (s). Smaller units of time include the millisecond (ms), microsecond (µs), and nanosecond (ns). Larger units of time usually are expressed in the nontraditional units of minutes, hours, days, and years.

Uncertainty in Measurement A digit that must be estimated is called uncertain. A measurement always has some degree of uncertainty.  Measurements are performed with instruments  No instrument can read to an infinite number of decimal places

Section 1.4 Uncertainty in Measurement Return to TOC Copyright © Cengage Learning. All rights reserved Measurement of Volume Using a Buret The volume is read at the bottom of the liquid curve (meniscus). Meniscus of the liquid occurs at about mL.  Certain digits:  Uncertain digit: 20.15

Precision and Accuracy Accuracy refers to the agreement of a particular value with the true value. Precision refers to the degree of agreement among several measurements made in the same manner. Neither accurate nor precise Precise but not accurate Precise AND accurate

Types of Error Random Error (Indeterminate Error) - measurement has an equal probability of being high or low. Systematic Error (Determinate Error) - Occurs in the same direction each time (high or low), often resulting from poor technique or incorrect calibration. This can result in measurements that are precise, but not accurate.

Uncertainty-Systemic Error l Systematic error- same direction each time l Want to avoid this l Bad equipment or bad technique. l Better precision implies better accuracy l You can have precision without accuracy l You can’t have accuracy without precision (unless you’re really lucky).

Rules for Counting Significant Figures - Details Nonzero integers always count as significant figures has 4 sig figs.

Rules for Counting Significant Figures - Details Zeros -Leading zeros do not count as significant figures has 3 sig figs.

Rules for Counting Significant Figures - Details Zeros -Captive zeros always count as significant figures has 4 sig figs.

Rules for Counting Significant Figures - Details Zeros Trailing zeros are significant only if the number contains a decimal point has 4 sig figs.

Rules for Counting Significant Figures - Details Exact numbers have an infinite number of significant figures. 1 inch = 2.54 cm, exactly  9 pencils (obtained by counting) - EXACT

Sig Fig Practice #1 How many significant figures in each of the following? m  5 sig figs kg  4 sig figs 100,890 L  5 sig figs 3.29 x 10 3 s  3 sig figs cm  2 sig figs 3,200,000  2 sig figs

Rules for Significant Figures in Mathematical Operations Multiplication and Division: # sig figs in the result equals the number in the least precise measurement used in the calculation. # sig figs in the result equals the number in the least precise measurement used in the calculation x 2.0 =  13 (2 sig figs)

Sig Fig Practice # m x 7.0 m Calculation Calculator says: Answer m 2 23 m g ÷ 23.7 cm g/cm g/cm cm x cm cm cm m ÷ 3.0 s m/s 240 m/s lb x 3.23 ft lb·ft 5870 lb·ft g ÷ 2.87 mL g/mL 2.96 g/mL

Rules for Significant Figures in Mathematical Operations Addition and Subtraction: The number of decimal places in the result equals the number of decimal places in the least precise measurement =  18.7 (3 sig figs)

Sig Fig Practice # m m Calculation Calculator says: Answer m 10.2 m g g g 76.3 g 0.02 cm cm cm 2.39 cm L L L L lb lb lb lb mL mL 0.16 mL mL

Complex sig figs l What if it uses both addition and multiplication rules? l Round when you change rules.

Measure your textbook using the four rulers provided and fill in the table in your Course Guide. Justify the precision for each of your measurements, and the number of significant figures in each of your calculations. React 1

Section 1.5 Significant Figures and Calculations Return to TOC Copyright © Cengage Learning. All rights reserved Example  300. written as 3.00 × 10 2  Contains three significant figures. Two Advantages  Number of significant figures can be easily indicated.  Fewer zeros are needed to write a very large or very small number. Exponential Notation

Copyright © Houghton Mifflin Company. All rights reserved.1–24 You have water in each graduated cylinder shown. You then add both samples to a beaker. How would you write the number describing the total volume? What limits the precision of this number? React 2

Section 1.5 Significant Figures and Calculations Return to TOC Copyright © Cengage Learning. All rights reserved Concept Check You have water in each graduated cylinder shown. You then add both samples to a beaker (assume that all of the liquid is transferred). How would you write the number describing the total volume? 3.1 mL What limits the precision of the total volume?

48 Section 1.5 Significant Figures and Calculations Return to TOC CH. 1 ASSIGNMENTS CW/HW: CH 1 ASSIGNED PROBLEMS: CW/HW: Ch1 - pg #19, 25, 27, 29, 31, 33, 35, 41, 45, 49bc, 51abc, 55, & (67-81 odd) due next Monday. *Activity: Metric Puzzles if time permits &/or Sig. Figs. activity Bingo #2/game/or other act.