1 Chapter OneMatter, Measurement, and Problem Solving

## How many sig figs are in each data?

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Chemistry is…

• …the study of the composition, structure, properties, changes that occur in matter. The properties of matter are determined by the properties of atoms and molecules.3 1.1 Atoms and Molecules

• Atoms are the tiny, fundamental building blocks of matter. • Atoms usually bind together in nature, forming molecules. (or ions. More later.)

Why do we study atoms and

molecules in such detail? Because THE PROPERTIES OF MATTER…4 1.2 The Scientific Approach to Knowledge

## What arithmetic operations were performed?

We also discuss several other topics like How are the electrons distributed in the atom?

We also discuss several other topics like What is the most common way of introducing recombinant DNA into bacterial cells?

• Best method (so far) for generating new knowledge. • Data and results may be qualitative (general observations) or quantitative (measurements).5 Scientific Laws • A scientific law is a statement (often mathematical) of behavior that is always the same under the same conditions. • Law: “This is what happens when XYZ…” • Boyle’s law: PV = a constant • Law of conservation of mass: Matter is neither created nor destroyed in a chemical reaction. Scientific Theories • A scientific theory is an explanation of a law.6 • A theory is NOT “an idea I just had.” Nor is it “a wild guess I came up with while hung over from last night.” • Example: the Law of Conservation of Mass is explained by atomic theory. Law: Mass of rust = mass of iron + mass of oxygen.

Theory: iron and oxygen atoms aren’t destroyed, they’re just

rearranged, so there is no change in mass.Science is: • testable • reproducible • explanatory • predictive Science is not: 7 • fair • democratic • absolute • based on authority• • tentative 8 • based on physical reality 1.3 The Classification of Matter

## How many sig figs are in the data?

We also discuss several other topics like What would be the DWL from allowing these two industries to pollute as much as they want?

Classified according to states (phases)

• Solid: ٭ _______shape ٭ _______volume • Liquid: ٭ _______shape ٭ _______volume • Gas: ٭ _______shape ٭ _______volume

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One Composition of Matter

Multiple component components11 Pure Substances and Mixtures

We also discuss several other topics like o Compensation- Lungs- increase respiratory rate to blow off that CO2 to get rid of hydrogen ions & correct that balance but how long can you breathe deep & fast?

• A pure substance (or just ‘substance’) has a fixed composition, and is either an element or a compound. • An element cannot be broken down into other simpler substances by chemical reactions. • A compound can be broken down by chemical reactions. • A mixture does not have a fixed composition. Mixtures can be separated by physical means.12Separating Mixtures

13141.4: Physical and Chemical Changes and Properties

We also discuss several other topics like the nurse is turning a client in bed. where would the nurse stand when using the friction-reducing sheet to turn the client to the opposite side of the bed?

Q: “Is XYZABC a chemical change?” A: “Have new substances been formed?”

15 Terms to Use: Properties

• A physical property can be observed without changing the composition of the matter. • To observe a chemical property there must be a change in composition. Q: “Is XYZABC a chemical property?” A: “Were new substances formed when you observed the property?”

Copper is red brown, opaque, solid: ______ properties.

Ethanol is flammable: a ______ property.16 Terms to Use: Properties

• An extensive property depends on the amount of matter present. ٭Length, mass, volume • An intensive property …doesn’t. ٭Color, odor, density, temperature 1.5 Energy

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• Energy is the ability to do work: Potential energy, kinetic energy, thermal energy, nuclear energy, electrical energy, etc.17 • Work—transfer of energy from applying a force through a distance. • Heat—energy transfer that occurs from a temperature difference.Energy, like matter, is conserved.

18 1.6 Units of Measurement

• SI: le Système International d'unités • In SI, there is only one unit for each type of measurement.

19 Metric Units and Prefixes

• Length: Meter • Mass: Kilogram • Time: Second • Temperature: Kelvin (not “degrees Kelvin”) • Derived units: ٭Volume: Liter (1 cubic decimeter), mL ٭Temperature: Degree Celsius (1 C°= 1 K) ٭Area: Square meter (m2; also cm2, km2, etc.) ٭Volume: Cubic meter (m3; also km3, cm3, etc. 1 cm3 = 1 mL)20 Density: An Important Derived Unit

Density: ratio of mass to volume: m d = ––– V • Mass and volume are extensive properties, but… • …their ratio is an intensive property. • Any units of mass and volume may be used. • Density can be used as a conversion factor.Prefixes Change the Magnitude of the Unit

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221.7 Reliability of Measurements

23 The last digit in a scientific measurement is the first uncertain

digit.24

Always estimate between graduations

25 Precision and Accuracy

• Accuracy: closeness of measurement to the “true” (accepted) value. • Precision: repeatability, reproducibility. ٭We never know—CAN’T know—whether a real measurement is accurate. ٭We usually make several measurements and strive for precision, expecting that good precision implies good accuracy. (Not necessarily true…)26 Significant Figures

Significant figure convention is designed so that our results represent both the magnitude and the precision of our measurements. 278 miles ————— = 23.76068376 mi/gal (calculator answer) 11.70 gallons Which one is the first uncertain digit? 27 Using Sig Fig Conventions

• Significant figures – all the known digits, plus the first uncertain digit. • The problem/calculation is completed before considering the number of sig figs. 1. Work the entire problem/calculation to get the “calculator” answer. 2. How many sig figs are in each data? 3. What arithmetic operations were performed? 4. Use #2 and #3 to determine the number of sig figs that should be reported in the final answer. 5. Round off the final answer appropriately.How many sig figs are in the data?

28 • Begin counting with the first non-zero digit. • Stop at the end of the number. Exceptions: • Counting numbers, defined numbers, and most conversion factors (2.54 cm = 1 in.) are considered to be exact (no uncertainty. • In exponential notation, the coefficient shows the number of sig figs. (e.g., 3.40 × 1012 has 3 sig fig). • Numbers ending in zero(es) without a decimal (e.g., 500 mL, 2200 g) are ambiguous.How many sig figs should I report in the final answer?

29 Base the number of sig figs in a result on measurements, not on known values. • Multiplication and division: ٭Report the same number of significant figures as the data with the fewest significant figures. • Addition and subtraction: ٭Report the same number of decimal places as the data with the fewest decimal places. • Addition/subtraction AND multiplication/division: ٭Use the rules above to determine the number of sig figs at each step in the calculation; continue until you reach the final answer.30 1.8 Solving Chemical Problems

• Determine the nature of the answer (its units); what are you trying to find? • Identify the given information: data, numbers, observations, constants, material you can look up, etc. • Devise a plan of attack.“Manuel, when faced with a problem you do not understand, do any part of it that you do understand, then look at it again.” --- R. Heinlein

31 Dimensional Analysis

A general problem-solving method involving conversions. • Number × 1 = that same number. • Fraction = 1 when numerator = denominator. • The same quantity or unit in numerator and denominator of a fraction will cancel. Conversion Factors

2.54 cm = 1 in. gives two conversion factors: 2.54 cm 1 in. ––––––– = 1 ––––––– = 132 1 in. 2.54 cm Now we can convert in. to cm or cm to in. Further Remarks on Solving Problems

• Does your answer represent physical reality? • A calculator always gives you an answer, but that answer is not always correct. Estimation can help determine whether an answer is reasonable. • Using an equation? All the variables but one are in the problem…somehow, somewhere. • Homework/exam problems: usually you are given just enough information to solve the problem.33 • Real-world problems: you usually have either too much information or not enough. Critical thinking is necessary.