Chem 2004 Post Lab Discussion 3 (PDF)

Chem 2004 Post Lab Discussion 3 Experiments 11-15 Structural Effects on Solubility Experiment 11  Solubility is the amount of solute that can dissolve in a given amount of solvent at a given temperature to form a homogenous solution. The process is called the dissolution proc...

Chem 2004 Post Lab Discussion 3 Experiments 11-15 Structural Effects on Solubility Experiment 11  Solubility is the amount of solute that can dissolve in a given amount of solvent at a given temperature to form a homogenous solution. The process is called the dissolution process. Attractive forces involved in dissolution: Attractive forces between solute particles Attractive forces between solvent particles Attractive forces between solute and solvent particles Energy must be supplied to overcome the first two. This energy is provided by the formation of bonds between the solute and solvent.  Dissolution may be: Physical process: Similarity in the structures of the solute and solvent will favor solubility. ‘Like dissolves like’. Polar solvents dissolves polar solutes. Nonpolar solvents dissolve nonpolar solutes. Chemical process: The substance dissolves in the solvent through a chemical reaction. A chemical reaction occurs. The solvent is called a reaction solvent.  H 2O Ether 5%NaOH 5%NaHCO3 5%HCl 88%H2SO4 H3PO4 Class Aniline - - + B Ethanol + + S1 Phenol - + - A2 Benzaldehyde - - - + - N2 Benzene - - - - I Glucose + - S2 Stearic acid - + + A1  The NH2 in aniline makes it basic. The ring is nonpolar. The OH in ethyl alcohol can form H-bonds with water, making it water soluble. While the ethyl group gives it nonpolar character to dissolve in ether (nonpolar). The H on the hydroxyl group in phenol is weakly acidic. To dissolve in the strong base (NaOH), but not in the weak base (NaHCO3) For benzaldehyde, the aromatic ring is very nonpolar. Neither the ring nor the carbonyl group are very reactive to our reagents and they are neither acidic nor basic.  Benzene is an aromatic hydrocarbon, it is highly nonpolar and has no functional groups that can react with the reagents, it is inert. The OH groups in glucose can form H-bonds with water, it is highly polar and water-soluble. This polarity prevents it from dissolving in ether which is nonpolar. The COOH in (18 carbon fatty acid) stearic acid makes it strongly acidic to dissolve in both a strong base and a weak base. Structural Effects on Reactivity Experiment 12 Displacement Of Hydroxyl (OH) Group In Alcohol (Lucas Reaction) Ethyl alcohol Isopropyl alcohol tert-butyl alcohol slowest or no rxn fast fastest ROH + HCl ZnCl → 2 RCl + H2O No reaction is observed with primary alcohols since the –OH group is difficult to remove or replace. The alkyl chlorides formed are responsible for the white ppt/cloudiness. Order of reactivity: 1° < 2° < 3° The tert-butyl carbocation is most stable due to hyperconjugation, thus the O–H is easiest to remove.  Ethyl alcohol (primary) CH3CH2OH Isopropyl alcohol (secondary) CH3CH(OH)CH3 Tertiary butyl alcohol has a steric hindrance (CH3)3COH CH3 CH3COH CH3  Decarboxylation Of Carboxylic Acids Oxalic acid White ppt. or cloudiness of limewater Acetic acid Clear sol’n The oxalic acid is easier to decarboxylate compared to the acetic acid due to the two carboxyl groups. There are more reactive pi bonds in the oxalic acid HOOCCOOH → HCOOH + CO2 CH3COOH → CH4 + CO2 (slower or requires more heat)  Reactivity Of Pi Electron Towards Oxidizing Agents Benzene Naphthalene no rxn Brown ppt. Benzene is inert since the pi electrons are evenly distributed and all bonds are equivalent and difficult to break/react with. Naphthalene’s 2 rings create a steric hindrance, making it easier to break bonds or react with. → no reaction KMnO4 → KMnO4 MnO2 + Hydrocarbons Experiment 13  Hydrocarbons Hydrocarbons refers to organic compounds containing only carbon and hydrogen. Alkanes are open-chain saturated hydrocarbons containing only carbon-carbon single bonds, or sigma bonds, or sp3 hybridized carbons. Alkenes are open-chained unsaturated hydrocarbons with double bonds, with sp2 or sp hybridized carbons. Alkynes are open-chained unsaturated hydrocarbons with triple bonds or sp hybridized carbons. Methane Methane (CH4) is an alkane with the following properties: odorless, colorless, tasteless gas. It is lighter than air, non-polar, and insoluble in water. It dissolves in non-polar solvents like alcohol, carbon tetrachloride, etc. Unreactive, except with fluorine, chlorine, halogens. It undergoes substitution reactions. Preparation Of Methane Gas Heating of anhydrous sodium acetate and soda lime (NaOH/CaO) produces methane gas and sodium carbonate. CH3COONa + NaOH → CH4(g) + Na2CO3(s) CaO calcium oxide/lime is a dehydrating agent, it does not participate in the reaction. The gas is collected via the water displacement method.  Ethene or Ethylene Ethene is an alkene found in coal gas and natural gas. In the lab it can be synthesized by cracking of large alkane molecules. Cracking is a process whereby large organic molecules are heated and broken up into smaller organic molecules. Ethene is a colorless gas with a sweet, irritating odor. It is insoluble in water. Due to the unsaturated carbons, alkenes react via addition reactions. Preparation Of Ethylene Gas The dehydration of ethanol with sulfuric acid and application of heat is an elimination reaction that will produce ethene H SO CH3CH2OH → 2 4 CH2=CH2 + H2O Sulfuric acid (H2SO4) acts as a dehydrating agent The gas is collected via the water displacement method  Chemical Properties/Reactions Methane Ethene Flammability (Color of Blue Yellow the flame, Luminosity) Reaction with Slowest to decolorize Faster to decolorize bromine Baeyer’s Test Decolorized KMnO4  Flammability The two burn with different colored flames due to their saturation/unsaturation. Only methane exhibits complete combustion with its blue flame. Ethylene exhibits incomplete combustion in their yellow-orange flames and in the soot produced in the test tube. CH4 + O2 → CO2 + H2O CH2=CH2 + O2 → CO2 + H2O + CO or C(s)  Reaction With Bromine Methane reacts with bromine in a substitution reaction, which involves the breaking of the existing bond and formation of a new bond. This is why it takes a much longer time to produce the desired result, the decolorization of the bromine (orange). CH4 + Br2 → CH3Br + HBr methyl bromide or bromomethane Ethene reacts with bromine in an addition reaction to the unsaturated carbons, which is faster than substitution since pi bonds are easier to break than sigma bonds. CH2=CH2 + Br2 → CH2(Br)CH2(Br) 1,2-dibromoethane  Baeyer’s Test A test for unsaturation, thus, methane (and other alkanes) does not react. CH4 + KMnO4/H2O → No rxn Ethene reacts quickly in an addition reaction. CH2=CH2 + KMnO4/H2O → CH2(OH)CH2(OH) + MnO2 (brown ppt.)  Solubility of Alkanes Solvent Kerosene Paraffin 1) Water insoluble Insoluble 2) Ether soluble Soluble 3) Ethyl alcohol insoluble Insoluble 4) Gasoline Soluble Soluble Reactivity of Alkanes Reaction with Kerosene Paraffin 1) Conc H2SO4 No rxn No rxn 2) Conc HNO3 No rxn No rxn 3) Conc NaOH No rxn No rxn  Kerosene and Paraffin are mixtures of alkanes. Therefore, they are nonpolar and are insoluble in polar solvents like water and ethyl alcohol. But they are soluble in nonpolar solvents like ether and gasoline (also a mixture of alkanes and other hydrocarbons) Additionally, they are unreactive to many reagents including strong acids and bases due to the strong sigma bonds found within the saturated alkanes which are difficult to break. Aldehydes and Ketones Experiment 14  Both have the same functional group which is the carbonyl carbon (C=O). However, for aldehydes, this group must be terminal, while for ketones, this group must not be terminal. General Formulas: RCHO and RCOR Aldehydes tend to have pungent odors, while ketones tend to have pleasant odors. Both are liquid at room temperature. The polar carbonyl group makes them more soluble in water compared to hydrocarbons, however, they are less soluble compared to alcohols.  Observation 1) Tollen’s Test with Silver Mirror Formaldehyde 2) Fehling’s Test with Brick red Ppt Formaldehyde 3) Bisulfate Addition with White (ice-like) precipitate Acetone 4) Auto-oxidation of White crystals or ppt Benzaldehyde  Oxidation Aldehydes are easily oxidized, while ketones cannot be oxidized. Thus, oxidation tests may be used to distinguish aldehydes from ketones. Aldehydes are oxidized to carboxylic acids. RCHO → RCOOH HCHO + [O] → HCOOH formaldehyde formic acid [O] → or methanal methanoic acid –C=O → –C=O H OH Sample Reactions: CH3CH2CH2CH2CHO → CH3CH2CH2CH2COOH IUPAC: Pentanal pentanoic acid Common: Valeraldehyde valeric acid CH3CH2CH2CH2COOH + CH3OH → CH3CH2CH2CH2COOCH3 pentanoic acid methanol methyl pentanoate valeric acid methyl alcohol methyl valerate Acetic acid CH3COOH  Tollen’s test: HCHO + 2 Ag(NH3)2OH → 2 Ag(s) + HCOOH +H2O + 4NH3 Fehling’s test: HCHO + 2 Cu2+ → HCOOH + Cu2O (red ppt.)  Addition Reaction with Sodium Bisulfite With acetone White crystals A test for acetone which forms CH3COCH3 + NaHSO4 → (CH3)2C(OH)SO3– Na+ + H2O CH3 CH3C–SO3– Na+ OH  Auto-oxidation of Benzaldehyde White crystals of benzoic acid form due to the exposure of the benzaldehyde to the oxygen in the air. + O2 → Carboxylic Acids and Acid Derivatives Experiment 15  Carboxylic Acids Carboxylic acids have the carboxyl functional group (COOH) which makes them highly polar and allows the short-chain acids to be soluble in water. The shorter chains are colorless liquids with sharp odors. Most reactions of carboxylic acids are nucleophilic substitutions which simply convert them into acid derivatives; RCOX, RCOOR’, RCOOM, RCOOCOR’, RCONH2 Properties of Acid Derivatives Acid halides: RCOX Reactivity decreases going Strong smelling, colorless liquids down this list. Acid anhydrides: RCOOCOR’ Acid chlorides may be Strong-smelling, colorless liquids reacted with to form the Esters: RCOOR’ less reactive derivatives. Sweet-smelling, colorless liquids Amides, being least Amides: RCONH2 reactive, cannot react to Neutral solids form the other derivatives.  Ethyl acetate Plastic balloon odor (or ethyl ethanoate) Preparation of Acid Derivatives The reaction of alcohols with carboxylic acids, forms esters. CH3CH2OH + CH3COOH → CH3COOCH2CH3 + H2O Esterification Acids may also be prepared by the reaction of alcohols with acid halides CH3CH2OH + CH3COCl → CH3COOCH2CH3 + HCl  Hydrolysis of Acid Derivatives Acetic anhydride Congo red paper turned black (acidic sol’n) Acetamide Litmus paper turned blue (basic vapor) CH3COOCOCH3 + H2O → 2CH3COOH Hydrolysis – to Or (CH3CO)2O break apart with water The acid derivatives CH3CONH2 + H2O → CH3COOH + NH3↑ are reverted back to the acid. Good Luck with your exams ☺