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Chapter 3

Chapter 3. Molecules, Ions, and their Compounds. Structure Determination of DNA. http://mrsec.wisc.edu/Edetc/background/DNA/index.html. DNA. NaCl, salt. Molecules, Ions & Their Compounds. Ethanol, C 2 H 6 O. Buckyball, C 60. MOLECULAR FORMULAS. Formula for glycine is C 2 H 5 NO 2

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Chapter 3

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  1. Chapter 3 Molecules, Ions, and their Compounds Dr. S. M. Condren

  2. Structure Determination of DNA http://mrsec.wisc.edu/Edetc/background/DNA/index.html Dr. S. M. Condren

  3. DNA Dr. S. M. Condren

  4. NaCl, salt Molecules, Ions& Their Compounds Ethanol, C2H6O Buckyball, C60 Dr. S. M. Condren

  5. MOLECULAR FORMULAS • Formula for glycine is C2H5NO2 • In one molecule there are • 2 C atoms • 5 H atoms • 1 N atom • 2 O atoms Dr. S. M. Condren

  6. Some Common Molecules Dr. S. M. Condren

  7. Example How many moles of ethyl alcohol (ethanol, C2H6O) are in a “standard” can of beer if there are 21.3 g of C2H6O? MM = 46.069 g/mol #mol = (21.3 g) (1 mol/46.069 g) = 0.462 mol Dr. S. M. Condren

  8. Example How many molecules of ethyl alcohol (ethanol, C2H6O) are in a “standard” can of beer if there are 21.3 g of C2H6O? MM = 46.069 g/mol #mol = 0.462 mol (0.462 mol) # molecules = (6.022x1023 molecules/mol) = 2.78x1023 molecules Dr. S. M. Condren

  9. Example How many C atoms are in a “standard” can of beer if there are 21.3 g of C2H6O? MM = 46.069 g/mol #mol = 0.462 mol = 2.78x1023 molecules # molecules (2.78x1023 molecules) #C atoms = (2 C atoms/molecule C2H6O) = 5.57x1023 C atoms Dr. S. M. Condren

  10. Molecular & Ionic Compounds NaCl Heme N Fe Dr. S. M. Condren

  11. Lithium Fluoride Dr. S. M. Condren

  12. -4 -3 -2 -1 +1 +2 Charges on Common Ions +3 By losing or gaining e-, atom has same number of e-’s as nearest Group 8A atom. Dr. S. M. Condren

  13. Announcement • Lab Safety Quiz must be completed by start of lab tomorrow with a perfect score • You can retake as many times as necessary • Lake Study is due on Friday Dr. S. M. Condren

  14. Announcement ATTN CHEMISTRY STUDENTS: Need a Tutor? Visit the GUTS DROP IN CENTER for FREE CHEMISTRY TUTORING! Where: 1ST FLOOR OF COLLEGE LIBRARY When: Sundays, 2pm-8pm, Mondays-Wednesdays, 2pm-6pm Just stop by and work with a tutor on homework or exam prep! No registration necessary. Detailed schedule: http://guts.studentorg.wisc.edu/dropinsummerschedule.htm With any other questions email the GUTS Office at guts@rso.wisc.edu or visit the website: http://guts.studentorg.wisc.edu Dr. S. M. Condren

  15. Predicting Charges on Monatomic Ions Dr. S. M. Condren

  16. Ion Formation Reaction of aluminum and bromine Dr. S. M. Condren

  17. Dr. S. M. Condren

  18. Combustion Analysis Dr. S. M. Condren

  19. Percentage Composition description of a compound based on the relative amounts of each element in the compound Dr. S. M. Condren

  20. EXAMPLE: What is the percent composition of chloroform, CHCl3, a substance once used as an anesthetic? MM = 1(gaw)C + 1(gaw)H + 3(gaw)Cl = (12.011 + 1.00797 + 3*35.453)amu = (12.011 + 1.00797 + 106.36)amu = 119.38amu 1(gaw)C1(12.011) %C = ----------- = ------------ X 100 = 10.061% C 119.38 119.38 Dr. S. M. Condren

  21. EXAMPLE: What is the percent composition of chloroform, CHCl3, a substance once used as an anesthetic? MM = 1(gaw)C + 1(gaw)H + 3(gaw)Cl = (12.011 + 1.00797 + 3*35.453)amu = 119.38amu 1(1.00797)H %H = ---------------- X 100 = 0.84436% H 119.38 Dr. S. M. Condren

  22. EXAMPLE: What is the percent composition of chloroform, CHCl3, a substance once used as an anesthetic? MM = 1(gaw)C + 1(gaw)H + 3(gaw)Cl = (12.011 + 1.00797 + 3*35.453)amu = 119.38amu 3(35.453)Cl %Cl = ----------------- X 100 = 89.095% Cl 119.38 Dr. S. M. Condren

  23. EXAMPLE: What is the percent composition of chloroform, CHCl3, a substance once used as an anesthetic? MM = 1(gaw)C + 1(gaw)H + 3(gaw)Cl = 119.377amu %C = 10.061% C %H = 0.84436% H %Cl = 89.095% Cl Dr. S. M. Condren

  24. Simplest (Empirical) Formula formula describing a substance based on the smallest set of subscripts Dr. S. M. Condren

  25. Acetylene, C2H2, and benzene, C6H6, have the same empirical formula. Is the correct empirical formula: C2H2 CH C6H6 Dr. S. M. Condren

  26. EXAMPLE: A white compound is formed when phosphorus burns in air. Analysis shows that the compound is composed of 43.7% P and 56.3% O by mass. What is the empirical formula of the compound? Multiply by Integer Divide by Smaller Element % (%/gaw) 1.41/1.41 = 1.00 P 43.7 43.7/30.97 = 1.41 2 2*1.00 56.3/15.9994 = 3.52 2*2.50 5 O 56.3 3.52/1.41 = 2.50 Empirical Formula => P2O5 Dr. S. M. Condren

  27. Example When analyzed, an unknown compound gave these experimental results: C, 54.0%; H, 6.00%, and O, 40.0%. Four different students used these values to calculate the empirical formulas shown here. Which answer is correct? Why did some students not ge the correct answer? (a) C4H5O2 (b) C5H7O3 (c) C7H10O4 (d) C9H12O5 Always round-off here Never round-off these numbers Dr. S. M. Condren

  28. EXAMPLE: A sample of a brown-colored gas that is a major air pollutant is found to contain 2.34 g of N and 5.34 g of O. What is the empirical formula of the compound? 2.34 %N = ----------------- X 100 = 30.5% N 2.34 + 5.34 5.34 %O = ----------------- X 100 = 69.5% O 2.34 + 5.34 Dr. S. M. Condren

  29. EXAMPLE: A sample of a brown-colored gas that is a major air pollutant is found to contain 2.34 g of N and 5.34 g of O. What is the empirical formula of the compound?%N = 30.5% N%O = 69.5% O Element % (%/gaw) N 30.5 30.5/14.0067 = 2.18 O 69.569.5/15.9994 = 4.34 Divide by Smaller 2.18/2.18 = 1.00 4.34/2.18 = 1.99 x1= 1 x1= 2 Empirical Formula => NO2 Dr. S. M. Condren

  30. Molecular Formula the exact proportions of the elements that are formed in a molecule Dr. S. M. Condren

  31. Molecular Formula from Simplest Formula empirical formula => EF molecular formula => MF MF = X * EF Dr. S. M. Condren

  32. Molecular Formula from Simplest Formula formula mass => FM sum of the atomic weights represented by the formula molar mass = MM = X * FM Dr. S. M. Condren

  33. Molecular Formula from Simplest Formula first, knowing MM and FM X = MM/FM then MF = X * EF Dr. S. M. Condren

  34. EXAMPLE: A colorless liquid used in rocket engines, whose empirical formula is NO2, has a molar mass of 92.0. What is the molecular formula? FM = 1(gaw)N + 2(gaw)O = 46.0 MM 92.0 X = ------- = -------- = 2 FM 46.0 thus MF = 2 * EF Dr. S. M. Condren

  35. What is the correct molecular formula for this colorless liquid rocket fuel? 2NO2 NO2 N2O4 Dr. S. M. Condren

  36. Example: A 100.00 g sample of CuSO4.XH2O was strongly heated to drive off the waters of hydration. After the heating, the sample weighed 63.92 g. What is the value of X? the formula of the hydrated compound? #g hydrate - #g anhydrous #g water = = 100.00g – 63.92g = 36.08g water #mol H2O = (36.08g H2O) (1 mol H2O/18.02g H2O) = 2.002 mol H2O (1 mol CuSO4/159.6 g CuSO4) (63.92g CuSO4) #mol CuSO4 = = 0.4005 mol CuSO4 = 5 X= (2.002 mol H2O/0.4005 mol CuSO4) Thus CuSO4.5H2O Dr. S. M. Condren

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