Scientific & Chemical Fundamentals Measurement, Conversions & Calculations Dr. Ron Rusay Fall 2007 © Copyright R.J. Rusay

Measurement & Units SI units & common units in General Chemistry (Lab Manual pp ) 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 R.J. Rusay

Units of Measure

Mass and Volume Measurements: Refer to pp. 5-8

Mass Determination (Weighing Devices: Balances)

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

Volume

Liquid Measurement Tools

Numbers & Measurement The Importance of Units  Measurement - quantitative observation consisting of 2 parts Part 1 - numberPart 1 - number Part 2 - unitPart 2 - unit  Examples: 20 grams20 grams 6.63    joules / second6.63    joules / second

Scale: Size & Comparison  Macroscopic vs. Microscopic  IBM financed Video: 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 Attosecond spectroscopy = x seconds Science, 317, , (2007) “The Electron Stopwatch”

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? milligrams 2.50 milligrams 3.1,000 milligrams 4.100,000 milligrams 1000 milligrams (mg) = 1 gram (g)

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

Numbers 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 R.J. Rusay

What is the length of the rod? Different measurement tools give different numbers: Which ruler is better? ? cm cm cm

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

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.

Temperature

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?Expressed in scientific notation? x 10 3 g

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

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

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

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

QUESTION Which one of the following does NOT represent a result with four significant digits?

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 © Copyright R.J. Rusay

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

Complete the following Units & Conversions 13,000,000,000 yrs.________________ __? gigayears 13 Gyrs Number Scientific Notation Named unit 1.3 x yrs ___________ mL ______________ mL Liters ____________ kg__8.45 x kg___ _? grams__ 5.46 X g L

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 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: cm

QUESTION If you were unloading a 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? kg kg kg kg

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

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? grams grams grams grams

Conversion Factor Method (Dimensional Analysis) Qualitative Descriptions vs. Quantitative Use exact numbers / “scale factor” UNITS A Bookkeeping Method: Example Short” ___ 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 © Copyright R.J. Rusay