Chemistry Semester Exam

Chemistry Semester Exam: Specific Study Guide Test 1st and 2nd period, Friday Dec. 19 Structure of Guide: I. Environmental Chemistry by Subject II. Everything Else by Subject – Guides, reactions, etc. Some topics are accompanied by page references for the green book. All sections are completed in order of the outline given. Notice that our most recent section, analytic chemistry, will be on the exam, despite thoughts to the contrary. It is on the hand-written outline Mrs. Nagel gave us.

I. Environmental Chemistry 1. Nitrates – pp.135-136 They are nutrients. Food for algae/microfauna in water. Present from fertilizer runoff; accumulated by eutrophication --overproduced with lack of DO (dissolved oxygen) in lakes Dying plants decompose anaerobically, build up, DO drops (cycle)

Nitrates are also present in drinking water, thanks to fertilizers and acid rain. They’re super-soluble, so HARD to remove (tertiary treatment necessary: see next section) Ingestion of too many nitrates can cause diseases in babies and cancer in adults 2. Waste Water – p. 137 Pollutants: heavy metals, particulates, pesticides, dioxins, nitrates, phosphates To get fresh water from sea water: distillation or reverse osmosis Treatment --sometimes raw sewage is released! It breaks down, but slowly… 1. Primary – removes solids and some oxygendemanding waste Uses filters and sedimentation tanks Flocculation: removal of suspended matter 2. Secondary – removes most oxygen demanding waste Uses aerobic bacteria to degrade waste Trickle filters and/or activated sludge 3. Tertiary – rarely done – removes heavy metals, nitrates, phosphates Precipitation of phosphates & ions Removes nitrates using ion exchange, denitrifying bacteria, or algal ponds 3. Chlorination/Ozoneation Formation of ozone: (UV catalyst)

O2  2O∙ O∙ + O2  O3 Depletion of ozone: (UV catalyst)

O3  O2 + O∙ O3 + O∙  2O2 Chlorination: Free-radical reaction: either

CCl2F2  CClF2 + Cl∙ Cl∙ + O3  ClO∙ + O2 ClO∙ + O∙  Cl∙ + O2

Or: Formation of halogenoalkanes 1. Initiating Cl2

Cl∙ + Cl∙

2. Propagating (2 subs) CH4 + Cl∙  CH3∙ + HCl And CH3∙ + Cl2  CH3Cl + Cl∙ (Remember that the two propagating steps eventually end in a Cl-free-rad) 3. Terminating (3 subs) Cl∙ + Cl∙

Cl2

Or

C2H5. ∙

C2H5.:C2H5

Or

Cl∙ + C2H5. ∙

C2H5Cl

4. Greenhouse Effect and Gases Gases: O3, CO2, H2O, CH4, NOx Water and Carbon dioxide are by far the main gases. Effect: Warming Earth by trapping/accumulation of radiation: Short-wave sunlight reflects from Earth’s surface as Longwave and is then absorbed by the gas bonds Too much greenhouse gas  over-heated atmosphere = global warming! 5. Global Warming Overaccumulation of CO2 and other gases  Temp. increase But: Ice core samples imply fluctuation in temperature for centuries! Still, there’s been a gradual temperature increase. Consequences: Agricultural/biodiversity changes; rising sealevels Particulates reverse global warming: they SCATTER & reflect radiation Leading to cooling! 6. Photochemical smog Occurs in “bowl-shaped” cities: less air circulation Occurs with temperature inversion: layer of warm air above cool air  Trapped pollutants

Photochemical: Reducing smog due to combustion Yellow-brown, SO2 w/soot, etc. Primary pollutants: NOx and VOC’s (volatile org’c cmpds)  converted to secondary in sunlight: see table below Formation of Secondary Pollutants (pay especial attention to top and bottom rxns) Nitrogen oxide NO2  NO + O∙ radicalization Hydroxyl radicalization O∙ + H2O  2OH∙ Nitric Acid formation OH∙ + NO2 HNO3 Radical Propagation OH∙ + RH  R∙ + H2O Peroxide Radical R∙ + O2  ROO∙ formation PAN formation Peroxide radical + nitrogen dioxide

II. General Chemistry 1. Isomers: Remember double/triple bonds and functional groups (eg. esters/carboxylic acids; ethers and alcohols and aldehydes; amines and amides) 2. IR Spectra: --Alcohol has a broad absorption at 3300 cm-1. --Fingerprint region: Far right side of graph. Unique to each molecule. --Functional groups: special absorptions (like alcohols, above) 3. NMR: Distinguish - # of peaks = H environments Area under = ratio of # of H’s (using relative heights) Splitting = # of neighbors for that environment (n+1) 4. Mass Spec: Used to determine abundance of isomers, molecular mass, and possible functional groups of a specific sample, thanks to fragmentation 5. Chromatography Adsorption: Adherence of a solute to a solid surface by chemical bond or physical attraction Partition: The ratio/equilibrium between mobile phase (elution of the solute) and stationary phase (adsorption of the solute)

6. Retention factor: Rf = Dist. Traveled by solute Dist. Traveled by solvent 7. Processes of Chromatography Paper: dot paper with solute, wet paper with solvent – observe dist. Traveled Thin Layer C: like paper, but on glass with a thin gel of silica as mobile phase Gas C: volatile sample is heated to gas in a capillary tube, with Helium as inert aid Column: Uses gel as mobile phase: eluent is poured over solute, which then seeps through gel in tube – sample can be recovered High-perform. Liquid C: Like gas, but more efficient—sample is forced by pressure through a short column/tube, using silica particles with alkane chains 8. Name/Draw Org’c compounds Alkanes, Alkenes, Alkynes Groups: carboxylic acids, esters, ethers, ketones, amines, amides, nitriles, halogenoalkanes

9. Reactions: (v. important) ADDITION a. Hydrogenation – Alkene + H2  Alkane (Platinum catalyst) b. Addition – Alkene + HX  Halogenoalkane c. Halogenation – Alkene + X2  “Double-halogen”-alkane d. Hydrolysis – Alkene + H2O  Alcohol POLYMERISATION Occurs through addition (using free radicals) or, more commonly, condensation Condensation also forms esters (carboxylic acid + alcohol = ester) OXIDISATION of ALCOHOLS (using Cr2O7-2) a. Primary – Distillation  Aldehyde Reflux  Carbox. Acid b. Secondary – Distillation/Reflux  Ketone c. Tertiary – NO REACTION!

10. Substitution Reactions (SN1 and SN2)

(from Oct. 27-28 guide) – in reverse: SN2, then SN1 Both SN1 and SN2 require warm conditions. SN2 – Subst’n, Nucleophilic, Bimolecular Single-Step, produces Intermediate (that annoying thing in brackets):

Notice that the OH group (reversed to show that the oxygen is really the important thing) is sneaking up on the carbon from the opposite side from the Br. That’s what SN2 reactions do: they give twotiming (get it? 2-timing!! Ha ha…) OH groups the chance to grab those poor primary carbons from behind. If the carbons were surrounded with a bunch of buddies, then the little SN2’s couldn’t do that: only a big, tough, “number one” SN1 can (get it? Number 1!! Hee hee)… which brings us to: SN1 – Subst’n, Nucleophilic, unimolecular These are the fast, strong, two-step processes that beat up even carbons that travel surrounded by lots of themselves (ie, tertiary):

1.

2.

SLOW step

FAST step

Substitution involving nitrogen: A NITRILE is an R-C≡N. Name it using the longest chain including N, then add “-nitrile” at end. So the root (eg ethanenitrile) is one word. Remember formations of amines: Ammonia is a nucleophile and forms amines with halogenoalkanes. (SN2) The cyanide ion forms a nitrile with halogenoalkanes (SN2) and then reacts with H2 and nickel to form an amine. It can THEN react with water to form a carboxylic acid and ammonium ions. Remember esterification (alcohol + acid) and formation of amides: Acid + amine  amide (name with N prefix followed by normal name, then –amide) 4. Elimination Reactions: Formation of Alkenes E2: Transition (intermediate) state; E1: Carbocation –like SN. Occur in HOT conditions with concentrated, alcoholic NaOH E1: Tertiary Carbon: halogen detaches, forms carbocation Then (step 2) a hydrogen on the cation joins OH- and forms water, while the extra electrons from the lost H form a double bond between the Carbons! It’s like the halogen is a shoe, and it comes off. So the foot (the H) goes to join a massage parlor (the OH group) and the legs are left to double bond themselves, unable to walk but now stronger than ever. …yes. E2: Primary Carbon: Halogen detaches AS the hydrogen leaves for the OH, and electrons join the carbons as usual. One step. It’s like a clean breakup. The halogen and hydrogen both leave the carbons for greener pastures and better fish, so the electrons are the rebound relationship—which is really clingy and double-bonded, because the carbons are lonely and traumatized. Got it?

_______________ That’s it for this guide! Please be sure to look over your notes, especially on reactions. The theoretical explanations may not have fixed information as well as complicated drawings might have. Remember that your green book is your friend. It loves you! Good luck on the exam, everyone. Peace on earth!