Scientific & Chemical Fundamentals

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Scientific & Chemical Fundamentals Dr. Ron Rusay Spring 2008 © Copyright 2003-2008 R.J. Rusay

Scientific & Chemical Fundamentals Chemistry & the Scientific Method Matter : Classification & Properties Mathematics / Arithmetic: Exponents, Significant Figures Measurement & Units: (SI & metric) Conversions and Relationships: Dimensional Analysis: Density, Percent VOCABULARY: Key Terms, Bold Style Learning © Copyright 1998-2008 R.J. Rusay

Textbook Reading Chemical Foundations 1.1 Chemistry: An Overview 1.2 The Scientific Method 1.3 Units of Measurement 1.4 Uncertainty in Measurement 1.5 Significant Figures and Calculations 1.6 Dimensional Analysis 1.7 Temperature 1.8 Density 1.9 Classification of Matter

Science & The Scientific Method

Law vs. Theory Figure: 01-15

QUESTION The difference between a scientific law and a scientific theory can, at times, be confusing. For example, we will refer to the “Atomic theory” or perhaps the “Law of Gravity.” Should the Law of Gravity be changed to the Theory of Gravity? 1. Yes, no one can see gravity, it is better described as a theory. 2. No, scientific laws are based on summaries of many observations and gravity observations are well known and predictable. 3. Yes, gravity is better described as a theory because gravity explains why masses attract each other and theories are about explaining observations. 4. No, keep it as a law, laws offer explanations and gravity explains why masses attract each other and laws are about explaining observations. HMClass Prep: Figure 1.5

ANSWER Choice 2 follows the agreed-upon distinction between a theory and a law. Observations that consistently agree and provide the same result in a variety of systems become “Laws.” Theories are attempts to offer human interpretations and explanations about what was observed. Therefore, we should continue calling the summary about attractions the Law of Gravitation. Section 1.2: The Scientific Method

Some Possible Steps in the Scientific Method 1. Observations qualitative quantitative 2. Formulating hypotheses possible explanation(s) for the observation 3. Performing experiments gathering new information testing whether the hypotheses are valid 4. Developing a theory 5. Testing & Refining

Chemistry: The Study of Matter In all of its forms & all of its behaviors Sub-categories (not so distinct any longer) Organic: carbon Inorganic: non-carbon Organometallic: organic + inorganic Analytical: what?, how much?, how pure? Biological / Biochemistry: living organisms Physical: energy, changes, rates Nuclear: the nucleus Environmental: interdisciplinary, eg. Oceanography © Copyright 1998-2008 R.J. Rusay

Chemistry & Matter (Chemicals) How many different chemicals do you think have been reported in the scientific literature? A) 100,000 B) 1,000,000 C) 10,000,000 D) 100,000,000 E) 1,000,000,000 CAS Registry : ~12,000 in 1907; > 31 million June 2007 Today ~ 500 new molecules are added / hr

Chemistry & Matter: Properties & States Physical vs. Chemical Properties Solid (s), Liquid (l), Gas (g) Homogeneous vs. Heterogeneous Mixtures Organization of atoms/molecules: atoms/elements  molecules/compounds Extensive vs. Intensive Properties Varies with amount (extensive) or does not vary with amount (intensive) © Copyright 1998-2008 R.J. Rusay

Observations of Physical & Chemical Properties

States of Matter

Organization of Matter Classification of Matter leptons Up,down, strange, charm, bottom, top

Organization of Matter Classification of Matter leptons muons, tau, neutrinos up,down, strange, charm, bottom, top

Figure: 01-09

Using Physical & Chemical Properties: Distinguishing a Compound & a Mixture

The effects of a magnet on iron: filings in a mixture and atoms in a molecule.

Types of Mixtures Mixtures have variable composition of two or more components. A homogeneous mixture is a solution (for example, vinegar: water + acetic acid, or steel & bronze: solid metals) A heterogeneous mixture is, to the naked eye, clearly not uniform (for example, a bottle of ranch dressing with two layers: water + oil, or two solids: iron and sulfur)

Elements & Compounds Element: A substance that cannot be broken into simpler substances by chemical means, eg. Fe, Iron or S8 Sulfur Compound: A substance with a constant composition that can be broken down into elements only by chemical processes,eg. FeS, Iron (II) sulfide

Figure: 01-05a-d

Figure: 01-06

Figure: 01-10

Figure: 01-01

QUESTION Is a cup of coffee a homogeneous solution or a compound? Which of the following agrees with your reasoning? 1. The coffee in the cup is a homogeneous solution because it contains the same components throughout, but there are many compounds dissolved to make coffee. 2. The coffee in the cup is a compound because it has a set ratio of components that make it the same throughout. 3. The coffee in the cup is both a compound and a solution. It looks the same throughout like a true solution, yet it always has the same amount of each component. 4. The coffee in the cup is a heterogeneous solution not homogeneous because it contains distinct, different compounds dissolved to make coffee.

ANSWER Choice 1 provides the best reasoning. The coffee in the cup is a homogeneous mixture of components, making it a solution. The amount of each component can vary greatly from coffee bean to coffee bean. Compounds do not have a variable composition like solutions. Section 1.9: Classification of Matter

Measurement & Units (SI units & common units in General Chemistry) Quantitative vs. Qualitative MASS (Chem: gram; SI: kg) LENGTH (Chem: cm & others; SI: m) TEMPERATURE (Celsius & Kelvin; SI: K) VOLUME (Chem: mL; SI: Liter) CHEMICAL AMOUNT: Mole (mol) © Copyright 1998-2008 R.J. Rusay

Units of Measure

Mass and Volume Measurement

Mass Determination (Weighing Devices: Balances)

Volumes of regular shapes V = s 3 h V = l x w x h

Volume

Liquid Measurement Tools

Figure: 01-20

Numbers & Measurement The Importance of Units Measurement - quantitative observation consisting of 2 parts Part 1 - number Part 2 - unit Examples: 20 grams 6.63   joules / second

Scale: Size & Comparison Macroscopic vs. Microscopic IBM financed Video: http://www.wordwizz.com/imagendx.htm How would you compare your lifespan?.. to that of a dog? ….to the age of the earth?…How about the age of mankind to that of all life?.. ..the age of industrialized mankind to the age of mankind?

Graphic Comparisons

Powers of Ten: Scale

Shorthand Prefixes Language describes scale (prefixes) How many zeroes does yotta yotta yotta have?

Commonly used prefixes in Chemistry These should be known from memory.

Commonly used prefixes in Chemistry Figure: TB01-T05 Attosecond spectroscopy = 10 -15 x 10 -3 seconds Science, 317, 765-775, (2007) “The Electron Stopwatch”

1000 milligrams (mg) = 1 gram (g) QUESTION Conveniently, a U.S. nickel has a mass of approximately 5 grams. If you had one dollar’s worth of nickels what would be the mass of the nickels in milligrams? 1. 100 milligrams 2. 50 milligrams 3. 1,000 milligrams 4. 100,000 milligrams HMClass Prep: Table 1.2 1000 milligrams (mg) = 1 gram (g)

ANSWER Choice 4 shows the correct conversion. After determining that 20 nickels make up one dollar, then one dollar’s worth of nickels would have a mass of 100 grams. Next, the conversion between grams and milligrams can be performed by multiplying by 1,000 (because there are 1,000 milligrams per gram.) Section 1.3: Units of Measurement

Scientific Notation & Significant Digits Scientific Notation: A single digit followed by a decimal and a power of ten. Examples: 2,345 mL and 0.002340 g 2,345 mL = 2.345 x 10 3mL 0.002340 g = 2.340 x 10 -3 g

Numbers How many numbers should I include? Expressing a number correctly is determined by the method used in the measurement! How many numbers should I include? Significant Digits (Figures) Consider: the exactness of the measured value Short Hand expression translates the number: Scientific Notation © Copyright 1998-2008 R.J. Rusay

What is the length of the rod? Different measurement tools give different numbers: Which ruler is better? ? cm 4.2 - 4.3cm ? cm 4.24 - 4.25cm

What is the diameter of a circle? All measuring devices are not the same, and the values (numbers) that come from them indicate their limitations. Is there a better instrument to use other than a ruler?

What does each line represent? 1 mL What can be estimated? O.1 mL

Measurement Assignment http://chemconnections. llnl

Temperature Scales Relative to Water

“Normal” Body Temperature

QUESTION Dr. R. walks into class and claims, “It is very cold in here today. It feels like 242 K.” If that were the temperature, would you agree that you would feel cold? What would that be in Celsius degrees? 1. I agree, that would be 31°C. 2. I agree, that would be – 31°C. 3. I do not agree, that would be 31°C. 4. I agree, that would be –31.15°C. HMClass Prep: Figure 1.12

ANSWER Choice 2 provides a correct (very) cold temperature. The formula to use is K = °C + 273.15. However this must be rearranged slightly to yield K – 273.15 = °C. Since this is a subtraction, the correct value would have no numbers beyond the decimal point because 242 does not have numbers beyond the decimal point. Section 1.7: Temperature

Temperature

Precision & Accuracy QUESTIONS: 1) Rank the images from best to worst precision. c > b > a 2) Rank the images from best to worst accuracy. c > a > b

QUESTION Two Chem 120 students are each drinking a soft drink after class. The volumes of both containers are respectively listed as 375 milliliters. Philip remarks that the law requires bottlers to be very precise. Susan correctly responded: 1. If precision were the only requirement, bottlers could claim any volume as long as it was always very nearly the same volume. 2. Since precision is a requirement, bottlers have to get exactly 375 mL in every can. 3. Bottlers must have a precise average of all of the containers in a case of soft drinks equal to 375 mL. 4. If there were a difference of no more than +/- 1 mL between containers, the bottlers can sell their beverage. HMClass Prep: Figure 1.10

ANSWER Choice 1 best fits what scientists define as precise. High precision measurements may have closeness to a set goal (such as 375 mL in a can) but precision always means closeness within a set of measurements. If the volumes of 100 containers were within a range of 294 to 295 mL the volumes would be precise, but not accurately 375 mL. Section 1.4: Uncertainty in Measurement

Precision & Accuracy Numerical Data

QUESTION Rank the relative precision of the three sets of data: a), b) and c).The accepted value is 8.08. Average a) b) c) 8.38 7.99 average deviation a) b) c) +/- 0.57 +/- 0.03 +/- 0.04 Answer: Precision: a > c > b B) Precision: b > c > a C) Precision: a = b > c D) Precision: a > b > c

QUESTION Rank the relative accuracy of the three sets of data: a), b) and c).The accepted value is 8.08. Average a) b) c) 8.38 7.99 average deviation a) b) c) +/- 0.57 +/- 0.03 +/- 0.04 Accuracy: a > c > b B) Accuracy: b > c > a C) Accuracy: c > a = b D) Accuracy: a = b > c Answer:

Reporting Numbers Rules for Significant Digits (Figures) Nonzero integers always count as significant figures. 3456 g has how many sig figs? 4 sig figs. Expressed in scientific notation? 3.456 x 10 3 g

Reporting Numbers Rules for Significant (Digits) Figures Exact numbers (unit, conversion or scale factors) can have an infinite number of significant figures. 1 liter = 1,000. ml, exactly 1 inch = 2.54 cm, exactly

Systematic Problem Solving Dimensional/Unit Analysis How many mL of milk are in a1/2 gallon carton? 0.50 gal ? mL 1 gal = 4 qt 1 qt = 946 mL 0.50 gal | 1 qt | 946 mL | 4 gal | 1 qt = ? mL

Complete the following Units & Conversions Number Scientific Notation Named unit 1.3 x 1010 yrs 13,000,000,000 yrs. ________________ __? gigayears 13 Gyrs 546 5.46 X 10 2 ___________ mL ______________ mL 0.546 Liters 0.546 L 0.845 ____________ kg __8.45 x 10 -1 kg___ _? grams__ 845 g

Zeros Leading zeros do not count as significant figures. 0.0486 mL has how many sig figs? 3 sig figs. Number expressed in scientific notation? 4.86 x 10 -2 mL

Zeros Captive zeros always count as significant figures. 16.07 cm has how many sig figs? 4 sig figs. Number expressed in scientific notation? 1.607 x 10 1 cm

Zeros Trailing zeros are significant only if the number contains a decimal point. 9.300 kg has how many sig figs? 4 sig figs. Number expressed in scientific notation? 9.300 kg

QUESTION Which one of the following does NOT represent a result with four significant digits? 1. 0.07100 2. 0.7100 3. 0.7010 4. 0.0710 HMClass Prep: Rules for Significant Figures

ANSWER Choice 4 only has three significant digits. Note that the lone zero in front of the decimal point is not based on any measurement and the next zero serves only as a place holder not as a measurement. Section 1.5: Significant Figures and Calculations

Mathematics & Arithmetic Relative to method(s) of measurement Short Hand expression: Scientific Notation Numbers : How many to include? Quantitative vs. Qualitative Addition/Subtraction...... Multiplication/Division..... What is “significant”?.....Rounding Off http:dbhs.wvusd.k12.ca.us/SigFigsFable.html © Copyright 1998-2007 R.J. Rusay

Computational Rules Addition/Subtraction: Answer expressed to the least number of decimal places of the figures in the process Multiplication/Division: Answer expressed to the least number of significant figures © Copyright 1998-2007 R.J. Rusay

Addition Four students were each asked to measure a piece of wire and provide a total length for the four pieces. Report the result correctly: 16.346 cm

QUESTION If you were unloading a 23.50 kg box of books from your car and a “friend” added two more 482 gram chemistry books, how much in kg and using the rules for significant digits, would you be lifting? 1. 23.98 kg 2. 24.464 kg 3. 24.46 kg 4. 24.5 kg HMClass Prep: Table 1.2

ANSWER Choice 3 provides both the conversion and proper number of significant digits. Consider that the 482 grams of mass must be doubled (to include both books) and that 482 grams is 0.482 kg. When adding two measurements always report your answer to the same number of decimal places as the least precise measurement used in the calculation. In this case the answer should be reported to the hundredths place. Section 1.5: Significant Figures and Calculations

Mathematical Processes: Provide correct answers assuming each value (unit omitted) is written with the correct number of sig figs: 9.56370 9.61370

QUESTION The average mass of a certain brand of vitamin C tablets is 253 mg. What is the mass of three such tablets rounded to the proper number of significant digits? 1. 0.760 grams 2. 0.759 grams 3. 0.7590 grams 4. 0.253 grams HMClass Prep: Table 1.2

ANSWER Choice 2 provides three significant digits (and accurate math work). 3 tablets  253 milligrams = 759 milligrams, then dividing by 1,000 converts the milligrams to grams. Note the three is a count of the number of objects, not a measured quantity and 759 retains the same number of significant digits as the least found in related measurements. Section 1.5: Significant Figures and Calculations

Conversion Factor Method (Dimensional Analysis) Qualitative Descriptions vs. Quantitative Use exact numbers / “scale factor” UNITS A Bookkeeping Method: Example ___ ft___in --------> ? m (1 ft = 12 in; 2.54 cm = 1 in; 100 cm = 1 m) ___ft x 12 in/ft + ___in = ___in ___in x 2.54 cm/in x 1 m/100cm = ___m 5 5 5 5 65 1.651 65 © Copyright 1998-2007 R.J. Rusay

Density Density = Mass / Volume [g/mL or g/cm3; g/L] Least dense man-made solid substance: Aerogel, D = 3.025 x 10-3 g/cm3 http://eetd.lbl.gov/ECS/aerogels/aerogels.htm http://stardust.jpl.nasa.gov/spacecraft/aerogel.html Dair = 1.22 x 10-3 g/cm3 (1.22 g/L) Densest known substance: a White Dwarf http://antwrp.gsfc.nasa.gov/apod/ap961203.html 1.0 teaspoon = 3.0 T; D = ? g/cm3 (1 tsp = 4.93 mL; 1 mL = 1 cm3 ) © Copyright 1998-2007 R.J. Rusay

QUESTION Which would provide more grams of NaCl, sample one with a mass of 2,350 mg, or sample two, a solid with a volume of 2.00 cm3? (The density of solid salt is 2.16 g/cm3.) Report your choice and report the grams of the more massive sample. 1. Sample two; 1.08 grams 2. Sample two; 4.32 grams 3. Sample one; 2.35 grams 4. Sample one; 2.350 grams

ANSWER Choice 2 provides the accurate mass for 2.00 cm3 of salt. This mass is larger than the 2.35 gram sample. Be sure to solve for the mass of a sample from its density and volume by multiplying 2.00 cm3 × 2.16 g/cm3. Section 1.8: Density

Densities of Various Common Substances* at 20° C

QUESTION The volume of a sample can be obtained from its density and mass. If the mass of a sample of acid from a battery were 5.00 grams and the density was 1.2 g/mL, what would you report in mL and with the proper number of significant digits, as the sample volume? 1. 6.0 mL 2. 6.00 mL 3. 4.2 mL 4. 4.17 mL

ANSWER Choice 3 shows the correct volume for 5.00 grams of this sample. First, be sure to use the correct solution for solving volume from mass and density (V = m/D). Then recall that the significant digit pattern for dividing measurements is to retain the same number of significant digits in the answer as the least number in any of the related measurements. Section 1.8: Density

Percent A comparison based on normalization to 100. George Washington University: 64 unsealed addressed envelopes with $10 in each were dropped on campus in different classrooms. In economics 18 of 32 were mailed, in business, history and psychology 10 of 32 were mailed. What is the percent for each of the 2 groups of students? © Copyright 1998-2007 R.J. Rusay

Percent Continued The Professor conducting the study received 43.75% of the $640 in the mail. How much did he receive? How many of you would mail the envelop presuming no one knows you found it? One student mailed an empty envelop with the return address: Mr. IOU, 1013 Indebted Lane, Bankrupt City, MS (WSJ 1/18/95) © Copyright 1998-2007 R.J. Rusay