Chapter 2 : Section 2 UNITS OF MEASUREMENT 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 Units of measurement Quantity magnitude, size, or amount
5 2,000,000 Units compare what is measured 0.030o with defined size mL g feet Quantity has no meaning without the unit 5 mL feet 100 g 2,000,000 SI Measurement Le Systeme International dUnites Adopted 1960 as world-wide agreed upon
Base units standards 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 Clic k Here Visual Concept 2 Cli ck Here Weight measure of the
gravitational pull on matter Example : Moon has 1/6 weight Metric Prefixes Tera- T 1012 1 000 000 000 000 Giga- G 109 1 000 000 000 Mega- M 106 1 000 000 kilo- k 103 1000 hecto- h deka- da 102 100 10 10 --- deci- d 10-1 0.1 centi- c 10-2 0.01 milli- m 10-3 0.001 micro- u (mu) 10-6 0.000 001 nano- n 10-9 0.000 000 001 pico- p 10-12 0.000 000 000 001
Derived SI units Combination of SI base units Examples Area m2 LxW Volume m3 L x W x H Density Kg/m2 mass/ volume Molar mass Kg/mol mass/mole Speed : 2 measurements distanc divided by e time
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 Step the 1: density of aluminum. m 8.4 g Write density equation Step 2: List your variables Step 3: Rearrange the D =
D = ? m = 8.4 g V = 3.1 cm3 V = 3.1 cm3 = 2.7 g/cm3 Step 4: Replace variables in the equation Step 5: Solve Rearranging Equations D =
m V Solve for m: V x D = Step 1: Multiply both sides by V 2: Step Vs will cancel out leaving m by itself and on top Solve for V: Step 1: Multiply both sides by V 2: Step Divide both side by D
m V x V so: m = D x V D = Step 3: Rewrite the equation m V V x D = m V Step 3:
Rewrite the equation x V V x D = m D D so: V = m D Practice pg.40 #1-3 1. What is the density of a block of marble that occupies 310. cm3 and has a mass of 853 g? 2.75 g/cm3 2. Diamond has a density of 3.26 g/cm3. What is the mass of a diamond that has a volume
of 0.351 cm3? 1.14 g 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? 5.60 mL Density of Some Common Substances Substance Density (g/cm3) Air 0.0013 Feathers 0.0025 Wood(Oak) 0.6 - 0.9 Ice 0.92 Water 1.00 Bricks 1.84 Aluminum 2.70 Steel 7.80 Silver 10.50 Gold 19.30 Conversion Factors
Ratio derived from the equality between two different units that can be used to convert from one unit to the other Visual Concept Click Here Equalities 1 dollar = 4 quarters 1 kg = 1000 g 1 Km = 0.6213 miles 1 dollar 4 quarter 4 quarters or 1 dollar So: How many quarter are there = in $55 ? 55 x 4
= 220 quarters 1 dollars dollars quarters Making conversions Video Concept Click Here 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 1 km 0.6213 miles
= 17.7 km Sample Problem 2.2 Express a mass of 5.712 grams in milligrams and in kilograms. 5.172 g x 5.172 g x 1000 mg1 g 1 kg 1000 g = 5172 mg
= 0.005172 kg Practice 1 & 2 pg. 42 1. Express a length of 16.45 m in centimeters and in kilometers. 2. Express a mass of 0.014 mg in grams. Answers: 1. 1645 cm, 0.01645 km 2. 0.000 014 g