Definition of Chemistry Chemistry is the study of substances in terms of: Composition What is it made of? StructureHow is it put together? PropertiesWhat characteristics does it have? ReactionsHow does it behave with other substances?

Chemicals in Toothpaste

Matter Is what all materials are made of Has mass Occupies space Has characteristics called physical and chemical properties

Physical Properties Copper has physical properties: Reddish-orange Very shiny Excellent conductor of heat and electricity Solid at 25  C Melting point 1083  C Boiling point 2567  C Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings Physical properties are characteristics observed or measured without changing the identify of a substance: shape, physical state, odor and color.

States of Matter All substances known as matter exist in one of three forms or states: Solids Have definite volumes and shapes Liquids Have definite volumes, but take the shapes of containers Gases Have no definite volumes or shapes Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

A physical change occurs in a substance if there is a change in the state or in the physical shape. Physical Change Examples of physical changes: Paper torn into little pieces (change of size) Copper hammered into thin sheets Water evaporating (change of state) Water poured into a glass (change of shape)

Chemical Properties Chemical properties describe the ability of a substance to interact with other substances or to change into a new substance. Example: Iron has the ability to form rust when exposed to oxygen. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Chemical Change In a chemical change or chemical reaction, a new substance forms that has A new composition New chemical properties New physical properties Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings **DEMO

Classify each of the following changes as physical or chemical: A. Bleaching a white shirt B. Ice melting on the street C. Toasting a marshmallow D. Cutting a pizza E. Iron rusting on an old car

Scientific Method Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

At a popular restaurant, where Chen is the head chef, the following occur: Chen notices that sales of the chef’s salad have dropped. Chen decides that the chef’s salad needs a new dressing. In a taste test, four bowls of salad are prepared with four new dressings: sasame seed, oil and vinegar, blue cheese and anchovies. The tasters rate the dressing with the sesame seeds the best. After two weeks with the new dressing, Chen notices that the orders for the chef’s salad have doubled. Chen decides that the sesame dressing improved the sales of the chef’s salad because the sesame dressing improved the taste of the salad.

Chapter 2 Measurements

Measurement You make a measurement every time you: Measure your height Read your watch Take your temperature Weigh a cantaloupe Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Stating a Measurement In every measurement, a number is followed by a unit. Observe the following examples of measurements: Number and Unit 35 m 0.25 L 225 lb 3.4 hr

Units in the Metric System In the metric and SI systems, one unit is used for each type of measurement: MeasurementMetricSI Lengthmeter (m)meter (m) Volumeliter (L)cubic meter (m 3 ) Massgram (g)kilogram (kg) Timesecond (s)second (s) TemperatureCelsius (  C)Kelvin (K)

Scientific Notation Scientific notation Is used to write very large or very small numbers For the width of a human hair of m is written as: 8 x m Of a large number such as s is written as: 2.5 x 10 6 s Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Comparing Numbers in Standard and Scientific Notation Here are some numbers written in standard format and in scientific notation: Number in Standard Format Scientific Notation Diameter of Earth m1.28 x 10 7 m Mass of a human 68 kg 6.8 x 10 1 kg Length of a pox virus cm3 x cm

Select the correct scientific notation for each. A ) 8 x ) 8 x ) 0.8 x B ) 7.2 x ) 72 x ) 7.2 x 10 -4

Solution Select the correct scientific notation for each. A ) 8 x B ) 7.2 x 10 4

Write each as a standard number. A. 2.0 x ) 2002) ) B. 1.8 x ) ) )

Solution Write each as a standard number. A. 2.0 x ) B. 1.8 x )

. l l.... l 3... cm The markings on the meter stick at the end of the blue line are read as: The first digit 2 plus the second digit 2.7 The last digit is obtained by estimating. The end of the line might be estimated between 2.7– 2.8 as half-way (0.5) or a little more (0.6), which gives a reported length of 2.75 cm or 2.76 cm. Reading a Meter Stick

Known + Estimated Digits In the length reported as 2.76 cm, The digits 2 and 7 are certain (known) The final digit 6 is estimated (uncertain) All three digits (2.76) are significant including the estimated digit

Significant Figures

State the number of significant figures in each of the following measurements: A m B L C g D m

State the number of significant figures in each of the following measurements: A m2 B L4 C g1 D m3 Solution

Rounding Off Calculated Answers In calculations, Answers must have the same number of significant figures as the measured numbers. Often, a calculator answer must be rounded off. Rounding rules are used to obtain the correct number of significant figures. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Rounding Off Calculated Answers When the first digit dropped is 4 or less, The retained numbers remain the same rounded to 3 significant figures drops the digits 32 = 45.8 When the first digit dropped is 5 or greater, The last retained digit is increased by rounded to 2 significant figures drops the digits 884 = 2.5 (increase by 0.1)

Adding Significant Zeros Sometimes a calculated answer requires more significant digits. Then one or more zeros are added. Calculated AnswerZeros Added to Give 3 Significant Figures

Adjust the following calculated answers to give answers with three significant figures. A cm B g C. 8.2 L

Solution Adjust the following calculated answers to give answers with three significant figures. A. 825 cm First digit dropped is greater than 5. B gFirst digit dropped is 4. C LSignificant zero is added.

Calculations with Measured Numbers In calculations with measured numbers, significant figures or decimal places are counted to determine the number of figures in the final answer. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

When multiplying or dividing, use The same number of significant figures as the measurement with the fewest significant figures. Rounding rules to obtain the correct number of significant figures. Example: x = = 5.3 (rounded) 4 SF 2 SF calculator 2 SF Multiplication and Division

When adding or subtracting, use The same number of decimal places as the measurement with the fewest decimal places. Use rounding rules to adjust the number of digits in the answer one decimal place two decimal places 26.54calculated answer 26.5 answer with one decimal place Addition and Subtraction

For each calculation, round the answer to give the correct number of significant figures. A x 4.2 = 1) 9 2) 9.2 3) B ÷ 0.07 = 1) ) 62 3) 60 C = 1) 257 2) ) D = 1) ) ) 40.7

A x 4.2 = 2) 9.2 B ÷ 0.07 = 3) 60 C rounds to 257 Answer (1) D rounds to 40.7Answer (3) Solution *****

Exact Numbers Exact numbers are NOT measured and do NOT have a limited number of significant figures. They do NOT affect the number of sig figs in a calculated answer.

Metric and SI Prefixes

Indicate the unit that completes each of the following equalities: A m = 1) 1 mm 2) 1 km3) 1 dm B g = 1) 1 mg2) 1 kg3) 1 dg C. 0.1 s = 1) 1 ms2) 1 cs3) 1 ds D m = 1) 1 mm 2) 1 cm3) 1 dm

Indicate the unit that completes each of the following equalities: A m = 1 km (2) B g = 1 mg (1) C. 0.1 s = 1 ds (3) D m = 1 cm (2) Solution

Some Common Equalities

A conversion factor Is a fraction obtained from an equality Equality: 1 in = 2.54 cm Is written as a ratio with a numerator and denominator Can be inverted to give two conversion factors for every equality 1 in and 2.54 cm 2.54 cm 1 in Conversion Factors

Setting Up a Problem How many minutes are 2.5 hours? Given unit= 2.5 hr Needed unit=? min Unit Plan=hr min Set up problem to cancel hours (hrs). Given Conversion Needed unit factor unit 2.5 hr x 60 min = 150 min (2 SF) 1 hr Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

A rattlesnake is 2.44 m long. How many centimeters long is the snake? 1) 2440 cm 2)244 cm 3)24.4 cm

A rattlesnake is 2.44 m long. How many centimeters long is the snake? 2)244 cm 2.44 m x 100 cm = 244 cm 1 m Solution

Often, two or more conversion factors are required to obtain the unit needed for the answer. Unit 1 Unit 2Unit 3 Additional conversion factors are placed in the setup to cancel each preceding unit. Given unit x factor 1 x factor 2 = needed unit Unit 1 x Unit 2 x Unit 3 = Unit 3 Unit 1 Unit 2 Using Two or More Factors

How many minutes are in 1.4 days? Given unit: 1.4 days Factor 1 Factor 2 Plan: days hr min Set up problem: 1.4 days x 24 hr x 60 min = 2.0 x 10 3 min 1 day 1 hr 2 SF Exact Exact = 2 SF Example: Problem Solving

If a ski pole is 3.0 feet in length, how long is the ski pole in mm?

3.0 ft x 12 in x 2.54 cm x 10 mm = 1 ft 1 in. 1 cm Calculator answer: mm Needed answer:910 mm (2 SF rounded) Check factor setup: Units cancel properly Check needed unit: mm Solution