14Stoichiometry - Organic Chemistry Appendix ALKENES...

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Unformatted text preview: Organic Chemistry Appendix ALKENES Contain one or more double bonds HYDROCARBONS Simplest organic compounds Contain only ______________ CnH2n C C The C=CH or C=CC angle is __________ Alkanes saturated have the maximum number of H attached to the C skeleton. H C H C H H ethene (ethylene) H C H C H CH 3 Alkenes Alkynes Aromatic unsaturated have double or triple bonds propene (propylene) Rotation about double bond is ____________ LRSVDS CHEM 110 Stoichiometry 1 LRSVDS CHEM 110 Stoichiometry 2 Structural isomers: Butene C4H8 same molecular formula: different __________ There are several possible structures for a chain of 4 carbons with one double bond 1-butene 2-methylpropene 1-butene 2-methylpropene 2-butene Geometric isomers same molecular formula: different __________ cis-2-butene trans-2-butene 2-butene cis-isomer: same side trans-isomer: opposite side (across) For geometric isomers: atoms have the same structure (are joined in the same way), but arrangement in space (geometry) is different. cis-2-butene trans-2-butene For alkenes, geometric isomers occur because of the _________ rotation about the C= C bond. 3 CHEM 110 Stoichiometry 4 LRSVDS CHEM 110 Stoichiometry LRSVDS ALKYNES: CnH2n-2 Contain CC HCCH ethyne (acetylene) CH3CCH propyne Organic Chemistry Why are there so many organic compounds? (three special properties of carbon) What is a hydrocarbon? What are the four classifications of hydrocarbons and how do they differ? Know the names of the first 10 hydrocarbons and how to write the molecular and structural formula. Know the bond angle of a H-C-H bond in an alkane. Valence What is the valence of an atom, and how is it related to valence electrons? Know the rules of valence for an element and how to determine the valence. Be able to write the structural formula for a molecule using the rules of valence. Isomers What is the definition of isomer? Know what a straight chain alkane vs. a branched alkane is. Know that the prefix n- is used to signify a straight chain. 5 LRSVDS CHEM 110 Stoichiometry 6 bond angle is _________ CH3 CH2CCH CH3CCCH3 1-butyne 2-butyne structural isomers NO geometric isomers are possible LRSVDS CHEM 110 Stoichiometry Unsaturated Hydrocarbons What is the definition of saturated and unsaturated? Which hydrocarbons contain multiple bonds? Single bonds? In which hydrocarbons is the rotation about the C-C bond restricted? What does a -ene suffix indicate? An -yne suffix? Reactivity of alkanes Relatively inert; takes E to initiate reactions Combustion reaction; basis of use as fuels, gives off a lot of energy. Combustion of hydrocarbons Complete combustion (hydrocarbon + xs O2 CO2 + H2O) Incomplete combustion (xs hydrocarbon + O2 CO + H2O; basis of production of lethal CO gas when hydrocarbons burned in a closed space) Isomers What is a structural isomer? What is a geometric isomer? Which types of hydrocarbons do not have geometric isomers? Which do? Why? Give an example of each kind of isomer Functional Groups (NOT ether, amide, or ester) Definition of a functional group Know the name of each functional group Know the structure of each functional group Know how to identify them within a molecule. Properties of Alkanes Flexible Free rotation about the C-C bond BP increases as size (# of C) increases LRSVDS CHEM 110 Stoichiometry 7 LRSVDS CHEM 110 Stoichiometry 8 Lecture 14: Molecular analysis Read: HW: BLB 3.33.5 BLB 3:21a,c,e&f,25,29,37,49,51,53 Sup 3:18 Non-Carbonyl Functional Groups Alcohol; R-OH where R can't be H, polar, water soluble. Amines; R3N, weak bases, important physiologically Ether; R-O-R where R can't be H, polar, unreactive, used as solvents Know: molecular & empirical formulas formula & molecular weights "No Score" from Exam 1?? Not a problem--Go see Mike in 210 Whitmore Carbonyl Functional Groups Aldehyde; RCOH, unreactive, used as solvents Ketone; RCOR, unreactive, used as solvents Carboxylic Acids; RCOOH, weak acids, sour taste, product of air oxidation of alcohols (acetic acid = vinegar) Esters; RCOOR, sweet smelling Amides; RCONR, weak bases, essential parts of RNA and DNA LRSVDS CHEM 110 Stoichiometry 9 Need help?? Get help!! 1. 2. 3. 4. TAs in CRC (211 Whitmore); schedule on website Tutoring: 6:30-10:30 PM Sun-Thurs. SI--hours on Chem 110 website My office hours: T 1:00-2:30 & Th 6:45-7:45 PM in 201 Whitmore LRSVDS CHEM 110 Stoichiometry 10 CHEMICAL FORMULA Formula that gives the TOTAL number of elements in a molecule or formula unit. Types of Chemical Formulas MOLECULAR FORMULA Chemical formula with subscripts of the total number of atoms in each molecule. H 2O H2O2 O2 CH3CH2OH EMPIRICAL FORMULA Chemical formula with the smallest integer subscripts for a given composition. COEFFICIENTS AND SUBSCRIPTS 3O2 2O3 Changing the coefficient changes the__________ of that molecule, not the identity. Changing the subscripts changes the __________of the molecule. LRSVDS CHEM 110 Stoichiometry 11 STRUCTURAL FORMULA Chemical formula with structural information about connectivity and angles. LRSVDS CHEM 110 Stoichiometry 12 Connecting microscopic (atoms) to macroscopic (weight) Use Formula Weight (Molar Mass or Molecular Weight) Definition: Important Connections Formula weight Avagadro's number water Coefficient Subscript methanol Empirical Formula nickel(II) perchlorate Mass Percent LRSVDS CHEM 110 Stoichiometry 13 LRSVDS CHEM 110 Stoichiometry 14 Working With Formulas How many atoms are in the formula Mg3(PO4)2? a) 3 b) 5 c) 10 d) 13 Experimental Data often provides only the Empirical Formula How many moles of Mg3(PO4)2 are in a 10.0 g sample? a) 0.0380 moles b) 0.0595 moles c) 0.0431 moles How many atoms are in 10.0 g of Mg3(PO4)2? a) 2.591022 atoms b) 3.581022 atoms c) 2.291022 atoms d) 2.971023 atoms How do we find the molecular formula from experimental data? LRSVDS CHEM 110 Stoichiometry 15 LRSVDS CHEM 110 Stoichiometry 16 Working with mass percent 1. What is the mass percent of C in CO2? Connecting: Empirical formula (lowest ratio) to Molecular formula (ratio in molecule) (atoms of element)(AW) 100 % of element = FW of compound C = 12.01 amu O = 16.0 amu FW =12.01+2(16.0)=44.01 amu %C = 12.01 100 = 27.3% 44.01 %O = 2(16.0) 100 = 72.7% 44.01 2. I have 2g of a sample that is 54.2% C by mass. How many grams of C are in the sample? HINT: If % C in an unknown substance is 54.2%, a 100g sample of that substance contains 54.2g of C. OR, If we have 100 g of sample, % of element = mass of element 100 100 g sample (2 g of 54.2g of C sample) = 1.08gof C 100g of sample LRSVDS Note: percentages must add up to 100%. CHEM 110 Stoichiometry Alternately: 0.542 is the fraction of the sample that contains carbon. 17 CHEM 110 Stoichiometry 18 LRSVDS Now we can connect Empirical Formula to Mass Percent of Elements Given one quantity, we can calculate the other: Start with mass % of elements (i.e. empirical data) and calculate a formula or Start with the formula and calculate the mass % elements Sample Problem An analysis of nicotine, a poisonous compound found in tobacco leaves, shows that it is 74.0%C, 8.65% H and 17.35% N. Its molar mass is 162 g/mol. What are the empirical and molecular formulas of nicotine? LRSVDS CHEM 110 Stoichiometry 19 LRSVDS CHEM 110 Stoichiometry 20 Combustion Analysis Empirical formulas are often determined by combustion analysis: Working with balanced reactions; Stoichiometry 2C8H18 + 25O2 16CO2 + 18H2O Energy is conserved A 4 g sample of an alcohol produces 7.65 g of CO2 and 4.70 g of H2O upon combustion. What is the empirical formula of the alcohol? Mass is conserved Stoichiometry Coefficients are the ratio of ___________ of reactant to ______________ of product LRSVDS CHEM 110 Stoichiometry 21 LRSVDS CHEM 110 Stoichiometry 22 Stoichiometric Problem Solving If a clean burning engine burns 1 gallon of gasoline (assume it is pure octane, density 0.692 g/mL), how many kg of CO2 will it produce? 1. What is the balanced chemical reaction? To connect mass to moles, make a table: Note Connections! Balanced Combustion Reaction: 2C8H18 + 25O2 16CO2 + 18H2O 2. What do we know? a) 1 gallon octane 3. What do we need to find? Conservation of mass: 2600g excess a) Mass octane b) moles octane c) moles of CO2 d) mass of CO2 Formula Weight: 114.22 g/mol 32.00 g/mol 44.01 g/mol 18.02 g/mol Always identify the balanced chemical reaction first. Moles: 2C8H18 + 25O2 16CO2 + 18H2O LRSVDS CHEM 110 Stoichiometry 23 LRSVDS CHEM 110 Stoichiometry 24 ...
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