CH 108 Lab Midterm

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Comment on the reactivity of ethanol, 2-propanol, and t-butyl alcohol

Most reactive: Ethanol (primary) Least reactive: T-butyl alcohol (tertiary)

Structural differences: Saturated v. unsaturated hydrocarbons

Saturated: No multiple bonds Unsaturated: 1+ multiple bonds

Solubility differences between alcohols

Small alcohols - high solubility Longer alkyl chains - less soluble More hydroxyl groups - more soluble

Structural differences: Straight-chain v. cyclic hydrocarbons

Straight-chain: All carbons are lined up in a row Branched: 1 or more branches come off the main carbon chain Cyclic: Carbons form a ring rather than a chain

Predict the solubility of 1-butanol, 2-butanol, & t-butyl alcohol in water and acetone.

1-butanol: Most water-soluble/most reactive 2-butanol: Moderately soluble T-butyl alcohol: Least solubke

T-butyl alcohol

2-methyl-2-propanol Will not oxidize

Aliphatic

A compound containing carbon and hydrogen joined together in straight chains, branched chains or non-aromatic rings

Glycosidic bond

A glycosidic bond is a covalent bond in which a carbohydrate binds to another group, which could also be a carbohydrate. A glycosidic bond is found between the two glucose molecules in maltose. * Present in reducing sugars * Makes it possible for the ring to open and form an aldehyde, which can be oxidized to a carboxylic acid

Non-reducing sugar

A sugar which cannot serve as a reducing agent. An example is sucrose.

Solubility of acetic acid, benzoic acid, acetamide

Acetic acid - soluble (would be less soluble if R group was bigger)

Reaction of alkanes/alkenes/alkynes/aromatics with bromine

Add 5% bromine solution to each test tube: methane (gas), acetylene (gas), cyclohexane, toluene Gaseous: Observe immediate reactions, then set in the dark for 5 min and observe again. Use blue litmus paper to test for formation of HBr. Liquid: Note immediate reactions. Hexane - stays orange-red, acidic [Alkanes should not react unless exposed to UV light] Hexene - turns clear, neutral [Alkenes should turn colorless & form HBr - acidic] Cyclohexane - turns clear, weak acid [Alkynes should turn clear and form HBr - acidic] Toluene - stays orange-red, weak acid [Benzene should not react unless Lewis acid catalyst]

Structural differences between aldehydes & ketones

Aldehydes - carbonyl carbon bound to an H atom & an R group Ketones - carbonyl carbon bound to 2 R groups

Differences in reactivity between aldehydes & ketones

Aldehydes are more reactive, due to being more polar Ring structures (ex. benzaldehyde) less reactive

Hydrocarbons that do not contain a benzene ring are known as ...

Aliphatic

Reactivity of aliphatic aldehydes vs. aromatic

Aliphatic aldehydes react more readily than aromatic

Structural differences: alkanes, alkenes, alkynes

Alkanes: No multiple bonds (CnH2n+2) Alkenes: Double bonds (CnH2n) Alkynes: Triple bonds (CnH2n-2)

Cycloalkanes have molecular formulas that are identical to _____.

Alkenes

Test for alcohol solubility

Ethanol, 2-propanol, t-butyl alcohol Test each alcohol by adding them to 2 mL of solvent (water or acetone) until no longer soluble. RESULTS: Ethanol - Most Soluble (smallest molecules) 2-Propanol - Moderately Soluble T-butyl alcohol - Least Soluble (largest molecules) All soluble in acetone.

Structural differences of primary, secondary, tertiary alcohols

They differ by the # of carbons attached to the hydroxyl-bearing carbon * Primary = 1 carbon * Secondary = 2 carbons * Tertiary = 3 carbons

Potassium permanganate (KMnO4) can be used to oxidize aromatic alkanes to carboxylic acids. In the experiment that you are going to do, which compound should produce a carboxylic acid when it reacts with KMnO4?

Toluene

2-propanol

isopropyl alcohol Oxidize to ketone

Toluene

methylbenzene

Classes of carbohydrates

monosaccharides, disaccharides, polysaccharides

anomeric carbon

only carbon attached to two oxygens -OH may point up or down * Sugar will not act as a reducing agent (not readily oxidized)

Amines

organic compounds with an amino group Primary - N bonded to 2 H and 1 hydrocarbon Secondary - N bonded to 1 H and 2 hydrocarbons Tertiary - N bonded to 3 hydrocarbons

Structures of carboxylic acids, amides, amines

Carboxylic acids - At least 1 carboxyl group, very polar (both C-O bonds and O-H bond) Amides - The H from the hydroxyl portion of the carboxyl group is replaced by -NR2 (amine) Amines - Ammonia in which 1 or more H atoms are replaced with hydrocarbon side chains

Differences in reactivity: carboxylic acids, amides, amines

Carboxylic acids - can donate a proton, and H bond even after the proton is donated Amides - Do not donate protons, but can H bond if its R group allows it Amines - can accept a proton from an acid

Benzene

Consists of a ring of six carbon atoms with alternating single and double carbon-carbon bonds. Very stable

Aromatic

Cyclic hydrocarbon that contains pi bonds arranged so that electrons in the p orbital can interact with each other (conjugation)

Lucas' oxidation for secondary and tertiary alcohols

Ethanol, 2-propanol, t-butyl alcohol Add Lucas reagent to each alcohol. Shake vigorously, and record the time it takes to react. Positive = cloudy = Secondary (slow) or Tertiary (rapid) Alcohol RESULTS: Ethanol: - (clear) 2-Propanol: + (cloudy, delayed) T-butyl alcohol: + (cloudy, instant)

Jones' oxidation for primary and secondary alchols

Ethanol, 2-propanol, t-butyl alcohol Dissolve alcohols each in 1 mL of acetone. Add Jones reagent (Kr3Cr2O7) & observe. Positive = Color change from green to orange = Primary or Secondary Alcohol RESULTS: Ethanol: - (green) 2-Propanol: + (yellow?) T-butyl alcohol: + (orange)

Reducing sugar

Can be oxidized Has free aldehyde or ketone group All monosaccharides are reducing sugars

General formula of carbohydrates

C(H2O)n

Acetylene

C2H2 (ethyne) Unsaturated = reactive

Ethanol

C2H5OH Oxidize to aldehyde > carboxylic acid

Cyclohexane

C6H12 Saturated = Not very reactive

Methane

CH4 Saturated = Not very reactive

The reaction of calcium carbide (CaC2) with water (H2O) produces an acetylene (C2H2) molecule. What is the other product? (Hint: Account for all of the atoms not used to make the first product). CaC2(aq) + 2 H2O(l) → C2H2(g) +

Ca(OH)2 (calcium hydroxide)

DNP Test

Lab: Aldehydes & Ketones lab Overview: DNP reacts with carbonyl groups, producing a color change. Reacts with all aldehydes & ketones, but reacts differently for aromatic and aliphatic aldehydes. A "carbonyl" test. Procedure: Add aldehyde/ketone to test tube. Add 10% ethanol. Add DNP and shake gently. Positive: Precipitate forms (aromatic aldehydes show some delay) Results: Acetone - Precipitation Cyclohexanone - Precipitation Butyraldehyde - Mild precipitation, light orange Benzaldehyde - Most precipitation, bright orange (more delay)

Iodoform Test

Lab: Aldehydes & Ketones lab Overview: Iodoform solution reacts with methyl ketones, forming a yellow solid. Differentiates methyl ketones from larger ketones. (Methyl ketone test) Procedure: Add aldehyde/ketone to test tube. Add iodoform solution and swirl gently. Add 10% NaOH. Results: Acetone - Yellow precipitate All others - No precipitate

Chromic Acid Test

Lab: Aldehydes & Ketones lab Overview: Oxidizing agent reacts with aldehydes, changing color. (Aldehyde test) Procedure: Add aldehyde/ketone to test tube. Add acetone. Add chromic acid reagent and shake gently. Positive: Changes color from orange to green-blue (benzaldehyde more slowly) Results: Acetone: - Cyclohexanone: - Butyraldehyde: + Benzaldehyde: + (delay)

Test: Insolubility of carboxylic acids

Lab: Exploring & Identifying Carboxylic Acids, Amines, and Amides Overview: Procedure: Add deionized water to test tubes. Add the carboxylic acids and amides, and observe. Add NaOH and observe. Add HCl and observe. Positive: Results:

Test: Solubility of carboxylic acids

Lab: Exploring & Identifying Carboxylic Acids, Amines, and Amides Overview: Procedure: Add deionized water to test tubes. Add the carboxylic acids or amides. Add NaHCO3. Observe. Positive: Soluble Results: Acetic: + Benzanoic: -

Test: Primary, Secondary, Tertiary Amines

Lab: Exploring & Identifying Carboxylic Acids, Amines, and Amides Overview: Procedure: Add the amines to the test tubes, and note odor. Add benzenesulfonyl chloride to each test tube. Add NaOH, stopper and shake vigorously. Test the pH and if it becomes acidic, add more NaOH. Reaction is complete when oily benzenesulfonyl chloride and smell are gone. Record results. Next, add HCl until solution is acidic. Positive: Precipitate forms Results: AFTER NAOH Primary: - Secondary: + Tertiary: + AFTER HCL Primary: + Secondary: + Tertiary: -

Test: Amides

Lab: Exploring & Identifying Carboxylic Acids, Amines, and Amides Overview: Procedure: Add the carboxylic acids or amides to the test tubes. Add NaOH. Place in hot bath. Measure with red litmus paper, and observe. Positive: Results:

Benedict's test

Lab: Exploring and Identifying Carbohydrates Overview: Determines whether reducing sugar is present (ketoses > aldoses). WIll be positive for all aldose monosaccharides and alpha-hydroxy ketones. If negative - non-reducing sugar Procedure: Add Benedict's reagent to test tubes. Add 5 drops of each carb to the correct tube. Place tubes in boiling water bath. Remove and observe results. Positive: Color change from blue to orange (Aldehyde oxidized to carboxylic acid). Results: Glucose: + Fructose: + Sucrose: - Lactose: +

Barfoed's test

Lab: Exploring and Identifying Carbohydrates Overview: Differentiates mono- and disaccharides. Ketoses will be negative. Procedure: Add Barfoed's reagent to each tube. Add carbohydrates to the correct tube. Place the tubes in boiling water bath. Observe results at 0 min, 1 min, and 2 min. Positive: Both mono- and disaccharides react positively, but monosaccharides much more quickly (2-3 min). Results: Glucose: Fast Fructose: Fast Sucrose: Slow Lactose: Slow Amylose: -

Iodine test

Lab: Exploring and Identifying Carbohydrates Overview: Tests for starch (simple carbohydrates will be negative) Procedure: Add carbohydrates to the correct tubes. Add KI/I2 solurion. Record results at room temperature. Positive: Color change in the presence of iodine (yellow > blue) Results: Glucose: - Fructose: - Sucrose: - Lactose: - Amylose: +

Amides

Organic compounds whose molecules have a carbonyl nitrogen bond. They are the product formed in a reaction between a carboxylic acid and an amine.

What does it mean to be oxidized? What are the possible oxidation products for alcohols? How do these products differ structurally?

Oxidation is the loss of electrons, loss of water, a decrease in C-H bonds, and an increase in C-O bonds Possible products: - Aldehyde: carbonyl group bound to at least 1 H atom - Carboxylic acid: carbonyl group bound to -OH group - Ketones - carbonyl group bound to 2 carbon-containing groups

Reaction of alkanes/alkenes/aromatics with permanganate

Place 10 drops acetone in 3 test tubes. Add 2 drops hexane to a tube, 2 drops hexene to another tube, and 2 drops toluene to the remaining tube. Add 2 drop potassium permanganate to each tube, and record observations Hexane - Dark purple, no precipitate [Alkanes will not react] Hexene - Brown, precipitate [Alkenes will form brown precipitate] Toluene - Burgundy, precipitate [Benzenes will not react without heat]

Oxidation products of alcohols

Primary alcohols - Aldehydes > Carboxylic acids Secondary alcohols - Ketones Tertiary alcohols - None

Reducing agent

The electron donor in a redox reaction. Is oxidized, reduces the species it acts on


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