Chapter 1 Chemistry: The Central Science PDF

Chapter 1 Chemistry: the Insert picture from First page of chapter Central Science Copyright McGraw-Hill 2009 1  1.1 The Study of Chemistry Chemistry – the study of matter and the changes that matter undergoes Matter – an...

Chapter 1 Chemistry: the Insert picture from First page of chapter Central Science Copyright McGraw-Hill 2009 1  1.1 The Study of Chemistry Chemistry – the study of matter and the changes that matter undergoes Matter – anything that has mass and occupies space Copyright McGraw-Hill 2009 2  Chemistry you may already know – Familiar terms: molecules, atoms, and chemical reactions Familiar chemical formula: H2O Copyright McGraw-Hill 2009 3  Molecules can be represented several different ways including molecular formulas and molecular models. – Molecular models can be “ball-and-stick” or “space-fill.” Each element is represented by a particular color Copyright McGraw-Hill 2009 4 Copyright McGraw-Hill 2009 5 1.2 The Scientific Method Copyright McGraw-Hill 2009 6  1.3 Classification of Matter Matter is either classified as a substance or a mixture of substances. Substance – Can be either an element or a compound – Has a definite (constant) composition and distinct properties – Examples: sodium chloride, water, oxygen Copyright McGraw-Hill 2009 7  Substances Element: cannot be separated into simpler substances by chemical means. – Examples: iron, mercury, oxygen, and hydrogen Compounds: two or more elements chemically combined in definite ratios – Cannot be separated by physical means – Examples: salt, water and carbon dioxide Copyright McGraw-Hill 2009 8  Mixtures Mixture: physical combination of two or more substances – Substances retain distinct identities – No universal constant composition – Can be separated by physical means Examples: sugar/iron; sugar/water Copyright McGraw-Hill 2009 9 Molecular Comparison of Substances and Mixtures Atoms of an element Molecules of an element Molecules of a compound Mixture of two elements and a compound Copyright McGraw-Hill 2009 10  Types of Mixtures – Homogeneous: composition of the mixture is uniform throughout Example: sugar dissolved in water – Heterogeneous: composition is not uniform throughout Example: sugar mixed with iron filings Copyright McGraw-Hill 2009 11 Classification of Matter Copyright McGraw-Hill 2009 12  Classify the following Aluminum foil Baking soda Milk Air Copper wire Copyright McGraw-Hill 2009 13 Aluminum foil: substance, element Baking soda: substance, compound Milk: mixture, homogeneous Air: mixture, homogeneous Copper wire: substance, element Copyright McGraw-Hill 2009 14  States of Matter – Solid particles close together in orderly fashion little freedom of motion a solid sample does not conform to the shape of its container – Liquid particles close together but not held rigidly in position particles are free to move past one another a liquid sample conforms to the shape of the part of the container it fills Copyright McGraw-Hill 2009 15 – Gas particles randomly spread apart particles have complete freedom of movement a gas sample assumes both shape and volume of container. – States of matter can be inter-converted without changing chemical composition solid → liquid → gas (add heat) gas → liquid → solid (remove heat) States of Matter Copyright McGraw-Hill 2009 17  1.3 Scientific Measurement Used to measure quantitative properties of matter SI base units Copyright McGraw-Hill 2009 18 SI Prefixes Copyright McGraw-Hill 2009 19  Mass: measure of the amount of matter – (weight refers to gravitational pull) Temperature: – Celsius Represented by °C Based on freezing point of water as 0°C and boiling point of water as 100°C – Kelvin Represented by K (no degree sign) The absolute scale Units of Celsius and Kelvin are equal in magnitude – Fahrenheit (the English system) (°F) Copyright McGraw-Hill 2009 20 Equations for Temperature Conversions Copyright McGraw-Hill 2009 21  Temperature Conversions A clock on a local bank reported a temperature reading of 28oC. What is this temperature on the Kelvin scale? Copyright McGraw-Hill 2009 22  Practice Convert the temperature reading on the local bank (28°C) into the corresponding Fahrenheit temperature. Copyright McGraw-Hill 2009 23  Volume: meter cubed (m3) – Derived unit – The unit liter (L) is more commonly used in the laboratory setting. It is equal to a decimeter cubed (dm3). Copyright McGraw-Hill 2009 24  Density: Ratio of mass to volume – Formula: – d = density (g/mL) – m = mass (g) – V = volume (mL or cm3) (*gas densities are usually expressed in g/L) Copyright McGraw-Hill 2009 25  Practice The density of a piece of copper wire is 8.96 g/cm3. Calculate the volume in cm3 of a piece of copper with a mass of 4.28 g. Copyright McGraw-Hill 2009 26  1.4 Properties of Matter Quantitative: expressed using numbers Qualitative: expressed using properties Physical properties: can be observed and measured without changing the substance – Examples: color, melting point, states of matter Physical changes: the identity of the substance stays the same – Examples: changes of state (melting, freezing) Copyright McGraw-Hill 2009 27  Chemical properties: must be determined by the chemical changes that are observed – Examples: flammability, acidity, corrosiveness, reactivity Chemical changes: after a chemical change, the original substance no longer exists – Examples: combustion, digestion Copyright McGraw-Hill 2009 28  Extensive property: depends on amount of matter – Examples: mass, length Intensive property: does not depend on amount – Examples: density, temperature, color Copyright McGraw-Hill 2009 29 1.5 Uncertainty in Measurement Exact: numbers with defined values – Examples: counting numbers, conversion factors based on definitions Inexact: numbers obtained by any method other than counting – Examples: measured values in the laboratory Copyright McGraw-Hill 2009 30  Significant figures – Used to express the uncertainty of inexact numbers obtained by measurement – The last digit in a measured value is an uncertain digit - an estimate Copyright McGraw-Hill 2009 31  Guidelines for significant figures – Any non-zero digit is significant – Zeros between non-zero digits are significant – Zeros to the left of the first non-zero digit are not significant – Zeros to the right of the last non-zero digit are significant if decimal is present – Zeros to the right of the last non-zero digit are not significant if decimal is not present Copyright McGraw-Hill 2009 32  Practice Determine the number of significant figures in each of the following. 345.5 cm 4 significant figures 0.0058 g 2 significant figures 1205 m 4 significant figures 250 mL 2 significant figures 250.00 mL 5 significant figures Copyright McGraw-Hill 2009 33  Calculations with measured numbers – Addition and subtraction Answer cannot have more digits to the right of the decimal than any of original numbers Example: 102.50 two digits after decimal point + 0.231 three digits after decimal point 102.731 round to 102.73 Copyright McGraw-Hill 2009 34  Multiplication and division – Final answer contains the smallest number of significant figures – Example: 1.4 x 8.011 = 11.2154 round to 11 (Limited by 1.4 to two significant figures in answer) Copyright McGraw-Hill 2009 35  Exact numbers – Do not limit answer because exact numbers have an infinite number of significant figures – Example: A penny minted after 1982 has a mass of 2.5 g. If we have three such pennies, the total mass is 3 x 2.5 g = 7.5 g – In this case, 3 is an exact number and does not limit the number of significant figures in the result. Copyright McGraw-Hill 2009 36  Multiple step calculations – It is best to retain at least one extra digit until the end of the calculation to minimize rounding error. Rounding rules – If the number is less than 5 round “down”. – If the number is 5 or greater round “up”. Copyright McGraw-Hill 2009 37  Practice 105.5 L + 10.65 L = 116.2 L Calculator answer: 116.15 L Round to: 116.2 L Answer to the tenth position 1.0267 cm x 2.508 cm x 12.599 cm = 32.44 cm3 Calculator answer: 32.4419664 cm3 Round to: 32.44 cm3 round to the smallest number of significant figures Copyright McGraw-Hill 2009 38  Accuracy and precision – Two ways to gauge the quality of a set of measured numbers – Accuracy: how close a measurement is to the true or accepted value – Precision: how closely measurements of the same thing are to one another Copyright McGraw-Hill 2009 39  both accurate and precise not accurate but precise neither accurate nor precise Copyright McGraw-Hill 2009 40 Describe accuracy and precision for each set Student A Student B Student C 0.335 g 0.357 g 0.369 g 0.331 g 0.375 g 0.373 g 0.333 g 0.338 g 0.371 g Average: 0.333 g 0.357 g 0.371 g True mass is 0.370 grams Copyright McGraw-Hill 2009 41 Student A’s results are precise but not accurate. Student B’s results are neither precise nor accurate. Student C’s results are both precise and accurate. Copyright McGraw-Hill 2009 42  1.6 Using Units and Solving Problems Conversion factor: a fraction in which the same quantity is expressed one way in the numerator and another way in the denominator – Example: by definition, 1 inch = 2.54 cm Copyright McGraw-Hill 2009 43  Dimensional analysis: a problem solving method employing conversion factors to change one measure to another often called the “factor-label method” – Example: Convert 12.00 inches to meters Conversion factors needed: 2.54 cm = 1 in and 100 cm = 1 meter *Note that neither conversion factor limited the number of significant figures in the result because they both consist of exact numbers. Copyright McGraw-Hill 2009 44  Notes on Problem Solving Read carefully; find information given and what is asked for Find appropriate equations, constants, conversion factors Check for sign, units and significant figures Check for reasonable answer Copyright McGraw-Hill 2009 45  Practice The Food and Drug Administration (FDA) recommends that dietary sodium intake be no more than 2400 mg per day. What is this mass in pounds (lb), if 1 lb = 453.6 g? Copyright McGraw-Hill 2009 46  Key Points Scientific method Classifying matter SI conversions Density Temperature conversions Physical vs chemical properties and changes Precision vs accuracy Dimensional analysis Copyright McGraw-Hill 2009 47