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

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

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Dr. S. M. Condren DNA

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Dr. S. M. Condren NaCl, salt Buckyball, C 60 Ethanol, C 2 H 6 O Molecules, Ions & Their Compounds

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Dr. S. M. Condren Formula for glycine is C 2 H 5 NO 2Formula for glycine is C 2 H 5 NO 2 In one molecule there areIn one molecule there are –2 C atoms –5 H atoms –1 N atom –2 O atoms MOLECULAR FORMULAS

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Dr. S. M. Condren Some Common Molecules

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Dr. S. M. Condren Example C 2 H 6 O? How many moles of ethyl alcohol (ethanol, C 2 H 6 O) are in a standard can of beer if there are 21.3 g of C 2 H 6 O? MM = 46.069 g/mol #mol = (21.3 g)(1 mol/46.069 g) = 0.462 mol

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Dr. S. M. Condren Example C 2 H 6 O? How many molecules of ethyl alcohol (ethanol, C 2 H 6 O) are in a standard can of beer if there are 21.3 g of C 2 H 6 O? MM = 46.069 g/mol #mol = 0.462 mol # molecules = (0.462 mol) (6.022x10 23 molecules/mol) = 2.78x10 23 molecules

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Dr. S. M. Condren Example C 2 H 6 O? How many C atoms are in a standard can of beer if there are 21.3 g of C 2 H 6 O? MM = 46.069 g/mol #mol = 0.462 mol # molecules = 2.78x10 23 molecules #C atoms = (2.78x10 23 molecules) (2 C atoms/molecule C 2 H 6 O) = 5.57x10 23 C atoms

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

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Dr. S. M. Condren Lithium Fluoride

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

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Dr. S. M. Condren 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

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Dr. S. M. Condren 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 http://guts.studentorg.wisc.edu/dropinsummerschedule.htmguts@rso.wisc.eduhttp://guts.studentorg.wisc.edu

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

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

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Dr. S. M. Condren

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Combustion Analysis

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

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Dr. S. M. Condren EXAMPLE: What is the percent composition of chloroform, CHCl 3, 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) C 1(12.011) %C = ----------- = ------------ X 100 = 10.061% C 119.38 119.38

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Dr. S. M. Condren EXAMPLE: What is the percent composition of chloroform, CHCl 3, 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

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Dr. S. M. Condren EXAMPLE: What is the percent composition of chloroform, CHCl 3, 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

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Dr. S. M. Condren EXAMPLE: What is the percent composition of chloroform, CHCl 3, 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

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

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Dr. S. M. Condren Acetylene, C 2 H 2, and benzene, C 6 H 6, have the same empirical formula. Is the correct empirical formula: C 2 H 2 CH C 6 H 6

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Dr. S. M. Condren 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? Element%(%/gaw) P O 43.7 56.3 43.7/30.97 = 1.41 56.3/15.9994 = 3.52 Divide by Smaller 1.41/1.41 = 1.00 3.52/1.41 = 2.50 Multiply by Integer 2*1.00 2*2.50 2 5 Empirical Formula => P 2 O 5

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Dr. S. M. Condren Never round-off these numbers Always round-off here 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) C 4 H 5 O 2 (b) C 5 H 7 O 3 (c) C 7 H 10 O 4 (d) C 9 H 12 O 5

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Dr. S. M. Condren 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? 5.34 %O = ----------------- X 100 = 69.5% O 2.34 + 5.34 2.34 %N = ----------------- X 100 = 30.5% N 2.34 + 5.34

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Dr. S. M. Condren 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 69.5 69.5/15.9994 = 4.34 Divide by Smaller 2.18/2.18 = 1.00 4.34/2.18 = 1.99 1 2 Empirical Formula => NO 2 x1=

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

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

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

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

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Dr. S. M. Condren EXAMPLE: A colorless liquid used in rocket engines, whose empirical formula is NO 2, 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 FM46.0 thus MF = 2 * EF

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Dr. S. M. Condren What is the correct molecular formula for this colorless liquid rocket fuel? 2NO 2 NO 2 N 2 O 4

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Dr. S. M. Condren Example: A 100.00 g sample of CuSO 4. XH 2 O 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? = 2.002 mol H 2 O (1 mol H 2 O/18.02g H 2 O)(36.08g H 2 O)#mol H 2 O = = 36.08g water = 100.00g – 63.92g - #g anhydrous#g hydrate #g water = #mol CuSO 4 = (63.92g CuSO 4 ) (1 mol CuSO 4 /159.6 g CuSO 4 ) = 0.4005 mol CuSO 4 X=(2.002 mol H 2 O/0.4005 mol CuSO 4 ) = 5 Thus CuSO 4. 5H 2 O

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