2. HOMEWORK Tomorrow you will be doing your first “real” lab! (Due to TurnItIn.com by Sun. 9/30 at 11:59 pm) Title: Density Blocks Lab Purpose: Determine the density/identity of up to three and at least one type of unknown metal. Materials: Metal shot, water, graduated cylinder, balance You must write a complete pre-lab tonight (including an ORIGINAL PROCEDURE and blank data table) & bring it to class if you want to participate tomorrow

3. DO NOW…. Which liquid has the highest density? 5 2 3 1 4 Coussement, DeSchepper, et al., Brain Strains Power Puzzles  2002, page 16 least dense 1 < 3 < 5 < 2 < 4 most dense

4. INTENSIVEproperty Density is an INTENSIVE property of matter. - does NOT depend on quantity of matter. -Examples: color, melting point, boiling point, odor, density DIFFERENT THAN EXTENSIVE properties - depends on quantity of matter. - mass, volume, length Styrofoam Brick Gold

5. Density M = DV D = M VM V V = M DM D D M V ensity ass olume

6. Comparing Densities (g/cm 3 ) Jaffe, New World of Chemistry, 1955, page 66 0.9 0.25 water 1.0 ice cork aluminum 2.7

7. Density of Some Common Substances Density of Some Common Substance Substance Density (g / cm 3 ) Air 0.0013* Lithium 0.53 Ice 0.917 Water 1.00 Aluminum 2.70 Iron 7.86 Lead 11.4 Gold 19.3 Density of Some Common Substance Substance Density (g / cm 3 ) 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 0 o C and 1 atm pressure

8. Consider Equal Masses Equal masses… …but unequal volumes. The object with the larger volume (aluminum cube) has the density. aluminum gold Dorin, Demmin, Gabel, Chemistry The Study of Matter, 3 rd Edition, 1990, page 71 smaller Christopherson Scales Made in Normal, Illinois USA

9. Density Practice Problems 1.What is the density of carbon dioxide gas if 0.196 g occupies a volume of 100. mL? 0.196 g 100. mL 1.96 x 10 -3 g/mL D = M VM V

10. 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? 1.75 g/mL x 5.0 mL 8.8 g M = D x V

11. Density Practice Problems 3.A sample of iron has a mass of 94 g and a density of 7.8 g/cm 3. What is the volume of the iron? 94 g 7.8 g/cm 3 12 cm 3 V = M DM D

12. Scientific Notation  Calculating with scientific notation (5.44 × 10 7 g) ÷ (8.1 × 10 4 mol) = 5.44 EE ÷ ÷ 78.1 = 671.6049383= 670 g/mol= 6.7 × 10 2 g/mol Type on your calculator: Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem EE = = 4

13. Significant figures: Rules for zeros Leading zeros are not significant. Captive zeros are significant. Trailing zeros are significant. Leading zero Captive zero Trailing zero 0.421 4012 114.20 – three significant figures – four significant figures – five significant figures

14. SI Prefixes mega-1,000,000 kilo-1,000 deci- 1 / 10 centi- 1 / 100 milli- 1 / 1,000 micro- 1 / 1,000,000 Also know… 1 mL = 1 cm 3

15. Practice Measuring 4.5 cm 4.54 cm 3.0 cm Timberlake, Chemistry 7 th Edition, page 7 cm 0 12345 0 12345 0 12345

16. 20 mL 10 mL 15 mL ? 15.0 mL

17. Practice Recording Temperature (Celcius) 0oC0oC 20 o C 40 o C 60 o C 80 o C 100 o CE 0oC0oC 10 o C 20 o C 30 o C 40 o C 50 o C 60 o C A 30.0 o C 0oC0oC 5oC5oC 10 o C 15 o C 20 o C 25 o CC 19.0 o C 60. o C

18. Scientific Notation  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. 65,000 kg  6.5 × 10 4 kg Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

19. Scientific Notation 2,400,000  g 0.00256 kg 7  10 -5 km 6.2  10 4 mm Practice Problems 2.4  10 6  g 2.56  10 -3 kg 0.00007 km 62,000 mm Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

20. 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

21. 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

22. Significant Figures  Calculating with Sig Figs  Multiply/Divide - The # with the fewest sig figs determines the # of sig figs in the answer. (13.91g/cm 3 )(23.3cm 3 ) = 324.103g 324 g 4 SF3 SF Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

23. Significant Figures (15.30 g) ÷ (6.4 mL) Practice Problems = 2.390625 g/mL  18.1 g 18.9g - 0.84 g 18.06 g 4 SF2 SF  2.4 g/mL 2 SF Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem