Chapter 2 - Introductory Chemistry, 2nd Edition Nivaldo Tro...

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1 Roy Kennedy Massachusetts Bay Community College Wellesley Hills, MA Introductory Chemistry , 2 nd Edition Nivaldo Tro Chapter 2 Measurement and Problem Solving 2006, Prentice Hall Tro's Introductory Chemistry, Chapter 2 2 What is a Measurement? • quantitative observation • comparison to an agreed upon standard • every measurement has a number and a unit Tro's Introductory Chemistry, Chapter 2 3 A Measurement • the unit tells you what standard you are comparing your object to • the number tells you 1.what multiple of the standard the object measures 2.the uncertainty in the measurement
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2 Tro's Introductory Chemistry, Chapter 2 4 Scientists have measured the average global temperature rise over the past century to be 0.6°C °C tells you that the temperature is being compared to the Celsius temperature scale 0.6 tells you that 1. the average temperature rise is 0.6 times the standard unit 2. the uncertainty in the measurement is such that we know the measurement is between 0.5 and 0.7°C Scientific Notation A way of writing large and small numbers Tro's Introductory Chemistry, Chapter 2 6 Big and Small Numbers • We commonly measure objects that are many times larger or smaller than our standard of comparison • Writing large numbers of zeros is tricky and confusing not to mention the 8 digit limit of your calculator! the sun’s diameter is 1,392,000,000 m an atom’s average diameter is 0.000 000 000 3 m
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3 Tro's Introductory Chemistry, Chapter 2 7 Scientific Notation • each decimal place in our number system represents a different power of 10 • scientific notation writes the numbers so they are easily comparable by looking at the power of 10 the sun’s diameter is 1.392 x 10 9 m an atom’s average diameter is 3 x 10 -10 m Tro's Introductory Chemistry, Chapter 2 8 Exponents • when the exponent on 10 is positive, it means the number is that many powers of 10 larger sun’s diameter = 1.392 x 10 9 m = 1,392,000,000 m • when the exponent on 10 is negative, it means the number is that many powers of 10 smaller avg. atom’s diameter = 3 x 10 -10 m = 0.0000000003 m Tro's Introductory Chemistry, Chapter 2 9 Scientific Notation • To Compare Numbers Written in Scientific Notation First Compare Exponents on 10 If Exponents Equal, Then Compare Decimal Numbers 1.23 x 10 -8 decimal part exponent part exponent 1.23 x 10 5 > 4.56 x 10 2 4.56 x 10 -2 > 7.89 x 10 -5 7.89 x 10 10 > 1.23 x 10 10
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4 Tro's Introductory Chemistry, Chapter 2 10 Writing Numbers in Scientific Notation 1 Locate the Decimal Point 2 Move the decimal point to the right of the first non-zero digit from the left 3 Multiply the new number by 10 n where n is the number of places you moved the decimal point 4 if the number is 1, n is +; if the number is < 1, n is - Tro's Introductory Chemistry, Chapter 2 11 12340 1 Locate the Decimal Point 12340 . 2 Move the decimal point to the
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Chapter 2 - Introductory Chemistry, 2nd Edition Nivaldo Tro...

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