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Chapter 2 : Section 2 UNITS OF MEASUREMENT

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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**

Units – compare what is measured with defined size mL g feet Quantity has no meaning without the unit 5 mL g ,000,000 feet

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**SI Measurement Le Systeme International d’Unites Base units**

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 (cm3) Graduated cylinder Water displacement Visual Concept 1 – Click Here Visual Concept 2 – Click Here Weight – measure of the gravitational pull on matter Example : Moon has 1/6 weight

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**Metric Prefixes Tera- T 1012 1 000 000 000 000**

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 Area m2 L x W**

Volume m3 L x W x H Density Kg/m2 mass/volume Molar mass Kg/mol mass/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 cm3 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 cm3. Calculate the density of aluminum. Step 1: m 8.4 g D = = = 2.7 g/cm3 Step 4: Write density equation V 3.1 cm3 Replace variables in the equation D = ? Step 2: m = 8.4 g Step 5: List your variables Solve V = 3.1 cm3 Step 3: Rearrange the equation

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**Rearranging Equations**

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

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Practice pg.40 #1-3 What is the density of a block of marble that occupies 310. cm3 and has a mass of 853 g? Diamond has a density of 3.26 g/cm3. What is the mass of a diamond that has a volume of cm3? 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? 2.75 g/cm3 1.14 g 5.60 mL

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**Density of Some Common Substances Substance Density (g/cm3)**

Air Feathers Wood(Oak) Ice 0.92 Water 1.00 Bricks 1.84 Aluminum 2.70 Steel 7.80 Silver 10.50 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 Visual Concept – Click Here 1 dollar 4 quarters 4 quarter or 1 dollar So: How many quarter are there in $55 ? = 4 quarters 55 dollars x = 220 quarters 1 dollars

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**Making conversions How many miles are in 15 Km? Write given value:**

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

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Sample Problem 2.2 Express a mass of grams in milligrams and in kilograms. 1000 mg 5.172 g x = 5172 mg 1 g 1 kg 5.172 g x = kg 1000 g

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Practice 1 & 2 pg. 42 Express a length of m in centimeters and in kilometers. Express a mass of mg in grams. Answers: cm, km g

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Measurement The International System of Units (SI) is the standard system used around the world.

Measurement The International System of Units (SI) is the standard system used around the world.

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