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

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

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

Dr. S. M. Condren DNA

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

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

Dr. S. M. Condren Some Common Molecules

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

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

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

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

Dr. S. M. Condren Lithium Fluoride

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

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

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

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

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

Dr. S. M. Condren

Combustion Analysis

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

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

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

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

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

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

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

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

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

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

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=

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

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

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

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

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

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

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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