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CHEM 1100 (7)
Chapter 2


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CHEM 1100
Kim Bolton

CH.2 THE CHEMIST’S TOOLBOX Measurement • Scientists must be curious and ask “why?” • They must make observations on some aspect of nature, devise laws from those observations and create a theory to give insight into reality  Tools needed for this procedure revolve around measurement Expressing Uncertainty in Measured Quantities • All measuring devices have limitations, therefore measurements always involve some uncertainty • Scientists report measured quantities in a way that reflects the precision associated with the measuring device • General rule for reporting measured quantities is:  Each digit in a reported quantity is taken to be certain, except for the last, which is estimated • When using measured quantities in calculations, must be careful to preserve the certainty associated with the measure quantities Scientific Notation • A number written in scientific notation has 2 parts: a decimal part, a number between 1 &10; a and an exponential part, 10 raised to the exponent, n. -10 exponent • 1.2 X 10 Decimal part exponential part • Meaning of n in the exponent:  Positive n = multiply by 10 n times  Negative n = divide by 10 n times • Positive n: 10 = 1 10 = 1 X 10 10 = 1 X 10 X 10 = 100 10 = 1 X 10 X 10 X 10 = 1000 • Negative n: 10 = 1/10 = 0.1 -2 10 = 1/10 X 10 = 0.01 CH.2 THE CHEMIST’S TOOLBOX -3 10 = 1/10 X 10 X 10 = 0.001 • To express a number in scientific notation: 1. Move the decimal point in the number to obtain a number between 1 and 10 (the decimal part) 2. Write the decimal part multiplied by 10 raised to the number of places you moved the decimal 3. The exponent is positive if you moved the decimal point to the left and negative if you moved it to the right. Units in Measurement • Most measurements require a unit, a fixed agreed upon quantity by which other quantities are measured • When making measurements, we must be consistent in our use of units • Numbers should always be written with their corresponding units, and units guide our way through calculations Important SI Standard Units Quantity Unit Symbol Length Meter m Mass Kilogram kg Time Second s Temperature Kelvin K SI Prefix Multipliers Prefix Symbo Multiplier l Giga G 1,009,000,000 (10 ) Mega M 1,000,000 (10 ) Kilo k 1,000 (10 ) Deci d 0.1 (10 )1 Centi c 0.01 CH.2 THE CHEMIST’S TOOLBOX -2 (10 ) Mili m 0.00-3 (10 ) Micro µ 0.000001 (10 )6 Nano n 0.0000000001 (10 )9 • The mass of an object is a measure of the quantity of matter within it • The volume of an object is a measure of the amount of space it occupies
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