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Chapter 2 : Section 2

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Objectives Distinguish between a quantity, a unit, and a measurement standard Name SI units for length, mass, time, volume, and density Distinguish between mass and weight Perform density calculations Transform a statement of equality to a conversion factor

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Units of measurement Quantity – magnitude, size, or amount 5 2,000, o Units – compare what is measured with defined size mL g feet Quantity has no meaning without the unit 5 mL 100 g 2,000,000 feet

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SI Measurement Le Systeme International d’Unites Adopted 1960 as world-wide agreed upon standards Base units

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Some SI Base Units Mass – measure of the amount of matter in an object Grams (g) Electronic scale or triple beam balance Volume – amount of space an object takes up Liters L V = L X W X H (cm 3 ) Graduated cylinder Water displacement Weight – measure of the gravitational pull on matter Example : Moon has 1/6 weight Visual Concept 1 – Click HereVisual Concept 2 – Click Here

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Metric Prefixes Tera- T Giga- G Mega- M kilo- k hecto- h deka- da deci- d centi- c milli- m micro- u (mu) nano- n pico- p

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Derived SI units Combination of SI base units Examples Aream 2 L x W Volumem 3 L x W x H DensityKg/m 2 mass/volume Molar massKg/molmass/mole Speed : 2 measurements distance divided by time

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Volume and Density Volume = Length x Width x Height 1 cm x 1 cm x 1 cm = 1 cm 3 Density = mass / Volume Sample Problem 2-1 A sample of aluminum metal has a mass of 8.4 g. The volume of the sample is 3.1 cm 3. Calculate the density of aluminum. Write density equation Step 1: D V = m List your variables Step 2: D V m = = = ? 8.4 g 3.1 cm 3 Replace variables in the equation Step 3: 8.4 g 3.1 cm 3 = Rearrange the equation Step 4: Solve Step 5: 2.7 g/cm 3 =

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Rearranging Equations D V = m Multiply both sides by V Step 1: Solve for m: D V = m D V = m VV x x V’s will cancel out leaving m by itself and on top Step 2: so: D= m Vx Solve for V: Rewrite the equation Step 3: Multiply both sides by V Step 1: Divide both side by D Step 2: D V = m VV x x D= m V x D D D V = m so: Rewrite the equation Step 3:

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Practice pg.40 # What is the density of a block of marble that occupies 310. cm 3 and has a mass of 853 g? 2. Diamond has a density of 3.26 g/cm 3. What is the mass of a diamond that has a volume of cm 3 ? 3. What is the volume of a sample of liquid mercury that has a mass of 76.2 g, given that the density of mercury is 13.6 g/mL? 1.14 g 2.75 g/cm mL

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Density of Some Common Substances Substance Density (g/cm 3 ) Air Feathers Wood(Oak) Ice 0.92 Water 1.00 Bricks 1.84 Aluminum 2.70 Steel 7.80 Silver Gold 19.30

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Conversion Factors Ratio derived from the equality between two different units that can be used to convert from one unit to the other Equalities 1 dollar = 4 quarters 1 kg = 1000 g 1 Km = miles 1 dollar4 quarters 4 quarter or1 dollar Visual Concept – Click Here = So: How many quarter are there in $55 ? 55 dollarsx 1 dollars 4 quarters = 220 quarters

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Making conversions How many miles are in 15 Km? 1. Write given value: 2. Choose conversion factor 3. Multiply top and divide bottom 11.0 miles x miles 1 km = 17.7 km Video Concept – Click Here

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Sample Problem 2.2 Express a mass of grams in milligrams and in kilograms g x 1 g 1000 mg = 5172 mg g x 1000 g 1 kg = kg

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Practice 1 & 2 pg Express a length of m in centimeters and in kilometers. 2. Express a mass of mg in grams cm, km g Answers:

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