OCHEM LAB Exp8

Carboxylic acids are structurally like

• Aldehydes (HC=O)

• Ketones (C-C=O)

The ____ of Carboxylic acids is a polar group with the carbon having slight excess of positive charge

• Carbonyl Carbon (C=O)

The _____ of Carboxylic acids have a slight excess of negative charge

• Oxygen

How to differentiate Carboxylic Acids from Aldehydes & Ketones?

• Carboxylic Acids have a Hydroxyl Group (-OH)

Structure of Carboxyl Group

• HO-C=O

The Carboxyl Group gives carboxylic acids its important characteristic as a/n ____

• Acid

Carboxylic acids are ____ acids which ionize only slightly in water

• Weak Acids

Carboxylic Acids:

• Vinegar = ____ taste = _____

• Lemon = ____ taste = _____

• Vinegar = tart taste = acetic acid

• Lemon = sour taste = citric acid

Carboxylic acids = ____ taste = ____ odors

Carboxylic acids = tart taste = unpleasant odors

Esters = ____ taste & ____ odors associated with _____

Esters = sweet taste & pleasant odors associated with fruits

These are used in the food industry as flavoring agents

• Ester

Rancid Butter = ____ acid = ____ odor

Rancid Butter = butyric acid = putrid odor

What is the artificial flavoring agent for Pineapples?

• ester ethyl butyrate

Odor and flavor of ORANGES

• octyl propanoate

Odor and flavor of PEARS

• pentyl propanoate

Odor and flavor of RASPBERRIES

• 2-methylpropyl methanoate

Why are Carboxylic Acids important?

• Most acids are derived from it

• the difference is usually in the OH portion of the structure

Name the 4 derivatives of Carboxylic acids according to the Lab Manual

1. Acyl Halides

2. Anhydrides

3. Esters

4. Amides

Name the 5 Carboxylic Acids we experimented on for SOLUBILITY

1. Acetic Acid

2. Oleic Acid

3. Stearic Acid

4. Succinic Acid

5. Benzoic Acid

Out of the 5 carboxylic acids, which ones were SOLUBLE and SLIGHTLY soluble in Distilled Water and Sodium Bicarbonate?

SOLUBLE:

• Acetic Acid

• Succinic Acid

Slightly Soluble

• Benzoic Acid

Why were Acetic and Succinic Acids SOLUBLE in water & NaHCO3?

They have small amounts of carbon

Which carboxylic acids had a MILD effervescence when came into contact with NaHCO3?

Slightly Soluble w/ Mild Effervescence:

• Benzoic Acid

INsoluble w/ Mild Effervescence:

• Stearic Acid

In the oxidation of Carboxylic Acids, which Oxidizing Agent was used?

• Potassium Permanganate (KMnO4)

Which carboxylic acids reduced KMnO4 to Mn2+?

• Acetic Acid

• Succinic Acid

Which carboxylic acids reduced KMnO4 to MnO2 (brown ppt)?

• Formic Acid

• Lactic Acid

• Oxalic Acid

What is the chemical formula of RUST?

Fe2O3

What specific acid did we use to remove RUST from white cloth?

Oxalic Acid

• Any acid or oxidizing agent will do

Fe2O3 + Oxalic Acid → ____ + H2O

• Fe Oxalate (a soluble salt)

Vinegar contains how much % of acetic acid?

4-6% Acetic Acid

What was the color change when litmus paper came into contact with ACETIC ACID?

Blue to Red

Which salts were ABSENT in vinegar?

• Carbonates (CO3)

• Sulfates (SO4)

• Phosphates (PO4)

• Halides

If Carbonates are present in vinegar, what would be the indicator?

Effervescence (bubbling) of Carbon Dioxide

What was added to the Vinegar Residue?

Concentrated HCl

If Sulfates are present in vinegar, what would be the indicator?

White PPT (Barium Sulfate [BaSO4] )

To test for presence of Sulfates, what was added to vinegar?

Barium Chloride = BaCl2

If Phosphates are present in vinegar, what would be the indicator?

Yellow PPT (Ammonium phosphomolybdate [ (NH4)3 P [Mo3O10]4 ]

To test for presence of Phosphates in vinegar, what were added?

• HNO3 = nitric acid

• NH4 MoO4 = ammonium molybdate

If Halides were present in vinegar, what would be the indicator?

White PPT of AgCl (Silver Chloride)

To test for the presence of halides in vinegar, what was added?

AgNO3 = Silver Nitrate

Chemical Formula for ESTERIFICATION of Carboxylic Acid

benzoic acid + ethanol → ethyl benzoate (C9 H10 O2)

What ester was formed from the ESTERIFICATION of benzoic acid?

ethyl benzoate

Ester → Odor

1. Ethyl Acetate

2. Methyl Acetate

3. Amyl Acetate

4. Ethyl Benzoate

1. Ethyl Acetate = nail polish remover odor

2. Methyl Acetate = liniment

3. Amyl Acetate = banana

4. Ethyl Benzoate = grapes/cherry

Esters → Miscibility in Water → Density

1. Ethyl Acetate

2. Methyl Acetate

3. Amyl Acetate

4. Ethyl Benzoate

Miscibility in Water → All had Formation of Layer (IMmiscible)

Density → All were less dense than water

What esters are found in RUM?

Ethyl Burtyrate

• Same as Pineapples

What esters are found in STRAWBERRIES?

Ethyl Formate

Esters are a combination of ____ and ____

Carboxylic Acid and Alcohol