1.2 The Scientific Method THE SCIENTIFIC METHOD The scientific method - a systematic approach to the discovery of new information. 2 Characteristics of the scientific process 1.Observation/Fact 2.Formulation of a question 3.Pattern recognition (often looking for cause-and-effect relationships)

1.2 The Scientific Method 4.Developing theories. This begins with a hypothesis - an attempt to explain the facts and their relationship. If the hypothesis is supported by many experiments it then becomes a theory. 5.Experimentation. Used to demonstrate the correctness of hypotheses and theories.

1.2 The Scientific Method 6.Summarizing information. A scientific law - the summary of a large quantity of information 7.Don’t forget serendipity – chance observations or “lucky mistakes”

Development of new experimentation and theory Further experimentation 1.2 The Scientific Method Observation of a phenomenon A question A hypothesis (a potential answer) Experimentation Theory New hypothesis

1.3 Exponential Notation Used to deal with very small or very large numbers as powers of 10 Examples: is written as 2 x ,000,000 is written as 4 x 10 6 Note: a negative exponent just means it’s a number less than 1

1.3 Significant Figures Significant Figures Not every number your calculator gives you can be believed Every measurement has error in it so the calculations do too

1.3 Significant Figures Significant figures - all digits in a number representing data or results that are known with certainty plus one uncertain digit.

1.3 Significant Figures The measuring device determines the number of significant figures a measurement has. In this section you will learn –to determine the correct number of significant figures (sig figs) to record in a measurement –to count the number of sig figs in a recorded value –to determine the number of sig figs that should be retained in a calculation.

For example, if you measured the length, width, and height of a block you could calculate the volume of a block: Length: 0.11 cm Width: 3.47 cm Height: cm Volume = 0.11cm x 3.47cm x 22.70cm = cm 3 Where do you round off? = 8.66?= 8.7? ?

1.3 Significant Figures RECOGNITION OF SIGNIFICANT FIGURES All nonzero digits are significant has 3 sig figs The number of significant digits is independent of the position of the decimal point Zeros located between nonzero digits are significant 4055 has 4 sig figs

1.3 Significant Figures Zeros at the end of a number (trailing zeros) are significant if the number contains a decimal point has 5 sig figs Trailing zeros are ambiguous if the number does not contain a decimal point versus 2000 Zeros to the left of the first nonzero integer are not significant (note: 4.5 x )

1.3 Significant Figures How many significant figures are in the following?

1.3 Significant Figures ,2,or 3 2

1.3 Significant Figures SCIENTIFIC NOTATION & Sig Figs Often used to clarify the number of significant figures in a number. Example: 4,300 = 4.3 x 1,000 = 4.3 x = 7.0 x 0.01 = 7.0 x 10 -2

1.3 Significant Figures SIGNIFICANT FIGURES IN CALCULATION OF RESULTS I.Rules for Addition and Subtraction The answer in a calculation cannot have greater significance than any of the quantities that produced the answer. example: 54.4 cm cm 54.4 cm 2.02 cm cm correct answer 56.4 cm

1.3 Significant Figures II. Rules for Multiplication and Division The answer can be no more precise than the least precise number from which the answer is derived. The least precise number is the one with the fewest sig figs. Which number has the fewest sig figs? The answer is therefore, 3.0 x 10 -8

For example, if you measured the length, width, and height of a block you could calculate the volume of a block: Length: 0.11 cm Width: 3.47 cm Height: cm Volume = 0.11cm x 3.47cm x 22.70cm = cm 3 Where do you round off? = 8.66?= 8.7? ?

1.3 Significant Figures Rules for Rounding Off Numbers When the number to be dropped is less than 5 the preceding number is not changed. When the number to be dropped is 5 or larger, the preceding number is increased by one unit. Round the following number to 3 sig figs: x 10 4 =3.35 x 10 4

1.4 Measurements MEASUREMENTS Consists of two parts a number AND a unit HAVE to have both E.g. I have a cat that is 3 days old? months old? years old?

ENGLISH AND METRIC UNITS English system - a collection of measures accumulated throughout English history. –no systematic correlation between measurements. –1 gal = 4 quarts = 8 pints Metric System - composed of a set of units that are related to each other decimally. –That is, by powers of tens 1.4 Measurement in Chemistry 11

1.4 Measurement in Chemistry Truly systematic -1 meter = 10 decimeters = 100 centimeters Basic Units of the Metric System Massgramg Lengthmeterm volumeliterL prefixes are used to indicate the power of ten used

Base units in the metric system 1.4 Measurements & Celsius ( ◦ C) & Joules (J)

1.4 Measurement in Chemistry mega (M)10 6 1,000,000. kilo (k)10 3 1,000. deka (da) deci (d) centi (c) milli (m) micro (  ) nano (n) Table 1.2 Some Common Metric Prefixes PrefixMultipleDecimal Equivalent

Metric System This table has Giga! 1.4 Measurements

Metric & English Systems Table 1.3 – no need to memorize

1.4 Measurements The milliliter and the cubic centimeter are equivalent so 1 mL = 1 cm 3

Mass and Weight Mass:Mass: the quantity of matter in an object –mass is independent of location Weight:Weight: the result of mass acted upon by gravity –weight depends on location; depends on the force of gravity at the particular location Common metric units:Common metric units: –1 kg = 1000g –1 mg = 0.001g 1.4 C. Measurements

1.4 Measurements Use the appropriate mass scale for the size object. –A dump truck is measured in tons –A person is measured in kg or pounds –A paperclip is measured in g or ounces –An atom? For atoms, we use the atomic mass unit (amu) –1 amu = x g

1.4 Measurements Length - the distance between two points –long distances are measured in km –distances between atoms are measured in nm. 1 nm = m Volume - the space occupied by an object. –the liter is the volume occupied by 1000 grams of water at 4 degrees Celsius ( o C) –1 mL = 1/1000 L = 1 cm 3

Time Units are the same for all systems (yeah!)Units are the same for all systems (yeah!) 60 s = 1 min 60 min = 1 h 1.4 D. Measurements

Temperature Fahrenheit (F):Fahrenheit (F): defined by setting the freezing point of water at 32°F and the boiling point of water at 212°F Celsius (C):Celsius (C): defined by setting freezing point of water at 0°C and boiling point of water at 100°C Will be given the conversions on tests 1.4 E. Measurements

1.4 Measurements The Kelvin scale is another temperature scale. It is of particular importance because it is directly related to molecular motion. As molecular speed increases, the Kelvin temperature proportionately increases. K = o C + 273

Temperature Kelvin (K):Kelvin (K): zero is the lowest possible temperature; also called the absolute scale –degree is the same size as Celsius degree K = °C E. Measurements

Temperature 1.4 E. Measurements

1.5 Unit Conversions UNIT CONVERSION You need to be able to convert between units -within the metric system -between the English and metric system The method used for conversion is called the Factor-Label Method or Dimensional Analysis !!!!!!!!!!! VERY IMPORTANT !!!!!!!!!!!

1.5 Unit Conversions Let your units do the work for you by simply memorizing connections between units. –For example: How many donuts are in one dozen? –We say: “Twelve donuts are in a dozen.” –Or: 12 donuts = 1 dozen donuts What does any number divided by itself equal? ONE! or...

1.5 Unit Conversions This fraction is called a conversion factor What does any number times one equal? That number.

We use these two mathematical facts to do the factor label method –a number divided by itself = 1 –any number times one gives that number back Example: How many donuts are in 3.5 dozen? You can probably do this in your head but let’s see how to do it using the Factor-Label Method. 1.3 Measurement in Chemistry

1.5 Unit Conversions Start with the given information dozen Then set up your unit factor... See that the units cancel... Then multiply and divide as needed… = 42 donuts

Factor-Label Method Conversion factorConversion factor –a ratio, including units, used as a multiplier to change from one system or unit to another –for example, 1 lb = g –Example: –Example: convert 381 grams to pounds –Example: –Example: convert gallons to milliliters 1.5 Unit Conversions

Density Density:Density: the ratio of mass to volume –most commonly used units are g/mL for liquids and solids, and g/L for gases. 1.7 Density and Spec Grav

1.7 Density and Spec. Grav. liquid mercury brass nut water cork

Density Example If 73.2 mL of a liquid has a mass of 61.5 g, what is its density in g/mL? Equation: D = M/V = M V