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DO NOW…. Which liquid has the highest density? least dense 1 < 3 < 5 < 2 < 4 most dense 1 3 2 5 4 Coussement, DeSchepper, et al. , Brain Strains Power Puzzles 2002, page 16 • Density is an Density INTENSIVE property of matter. - does NOT depend on quantity of matter. Styrofoam Brick -Examples: color, melting point, boiling point, odor, density • DIFFERENT THAN EXTENSIVE properties - depends on quantity of matter. - mass, volume, length Density M D = V M ass M = DxV V = M D ensity V olume D Density of Some Common Substance Density of Some Common Substances Substance Density (g / cm3) Air 0.0013* Lithium 0.53 Ice 0.917 Water 1.00 Aluminum 2.70 Iron 7.86 Lead 11.4 Gold 19.3 *at 0oC and 1 atm pressure Consider Equal Masses Equal masses… …but unequal volumes. The object with the aluminum larger volume (aluminum cube) has the smaller density. gold Christopherson Scales Made in Normal, Illinois USA Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3rd Edition, 1990, page 71 Comparing Densities (g/cm3) cork 0.25 0.9 ice water 1.0 aluminum 2.7 Jaffe, New World of Chemistry, 1955, page 66 Density Practice Problems 1. What is the density of carbon dioxide gas if 0.196 g occupies a volume of 100. mL? M D = V 0.196 g 1.96 x 10-3 g/mL 100. mL Density Practice Problems 2. An irregularly shaped stone has a volume of 5.0 mL. The density of the stone is 1.75 g/mL. What is the mass of this stone? M = DxV 1.75 g/mL x 5.0 mL 8.8 g Density Practice Problems 3. A sample of iron has a mass of 94 g and a density of 7.8 g/cm3. What is the volume of the iron? V = M D 94 g 12 cm3 7.8 g/cm3 Prefix Symbol Meaning Exponential Notation mega M 1,000,000 kilo k 1,000 hecto h 100 deka da 10 --- --- 1 deci d 0.1 centi c 0.01 milli m 0.001 micro µ 0.000001 nano n 0.000000001 Also know… 1 mL = 1 cm3 Practice Measuring 0 1 2 3 4 5 4.5 cm cm 0 1 2 3 4 5 4.54 cm cm 0 1 2 3 4 5 3.0 cm cm Timberlake, Chemistry 7th Edition, page 7 20 15.0 mL 15 mL ? 10 Practice Recording Temperature 60oC (Celcius) 100oC 25oC 50oC 80oC 20oC 40oC 60oC 15oC 30oC 40oC 10oC 20oC 20oC 5oC 10oC 0oC 0oC 0oC E C 18.0oC 60.oC A 30.0oC Scientific Notation Calculating with scientific notation (5.44 × 107 g) ÷ (8.1 × 104 mol) = Type on your calculator: 5.44 EE 7 ÷ 8.1 EE 4 = = 671.6049383 = 670 g/mol = 6.7 × 102 g/mol Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem Scientific Notation 65,000 kg 6.5 × 104 kg Converting into scientific notation: Move decimal until there’s 1 digit to its left. Places moved = exponent. Large # (>1) positive exponent Small # (<1) negative exponent Only include sig. figs. Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem Scientific Notation Practice Problems 2,400,000 g 2.4 10 6 g 0.00256 kg 2.56 10 -3 kg 7 10-5 km 0.00007 km 6.2 104 mm 62,000 mm Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem Percent Error Indicates accuracy of a measurement experimental accepted % error 100 accepted your value real value Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem Percent Error A student determines the density of a substance to be 1.40 g/mL. Find the % error if the accepted value of the density is 1.36 g/mL. 1.40 g/mL 1.36 g/mL % error 100 1.36 g/mL % error = 2.94 % Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem Significant Figures Counting Sig Figs All digits are significant EXCEPT… Leading zeros -- 0.0025 Trailing zeros without a decimal point -- 2,500 Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem Significant Figures Calculating with Sig Figs (con’t) Exact Numbers do not limit the # of sig figs in the answer. Counting numbers: 12 students Exact conversions: 1 m = 100 cm Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem Significant Figures Calculating with Sig Figs Multiply/Divide - The # with the fewest sig figs determines the # of sig figs in the answer. (13.91g/cm3)(23.3cm3) = 324.103g 4 SF 3 SF 3 SF 324 g Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem Significant Figures Practice Problems (15.30 g) ÷ (6.4 mL) 4 SF 2 SF = 2.390625 g/mL 2.4 g/mL 2 SF 18.9 g - 0.84 g 18.06 g 18.1 g Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem Significant figures: Rules for zeros Leading zeros are not significant. Leading zero 0.421 – three significant figures Captive zeros are significant. Captive zero 4012 – four significant figures Trailing zeros are significant. Trailing zero 114.20 – five significant figures Rules for Counting Significant Figures 1. Nonzero integers always count as significant figures. 2. Zeros: There are three classes of zeroes. a. Leading zeroes precede all the nonzero digits and DO NOT count as 2 significant figures. Example: 0.0025 has ____ significant figures. b. Captive zeroes are zeroes between nonzero numbers. These always 4 count as significant figures. Example: 1.008 has ____ significant figures. c. Trailing zeroes are zeroes at the right end of the number. Trailing zeroes are only significant if the number contains a decimal point. 3 Example: 1.00 x 102 has ____ significant figures. Trailing zeroes are not significant if the number does not contain a decimal 1 point. Example: 100 has ____ significant figure. 3. Exact numbers, which can arise from counting or definitions such as 1 m = 100 cm, never limit the number of significant figures in a calculation. Ohn-Sabatello, Morlan, Knoespel, Fast Track to a 5 Preparing for the AP Chemistry Examination 2006, page 53