Experiment #7: Aldehydes And Ketones

Question 1

IDENTIFICATION:

Aldehydes and Ketones with ____________ are soluble in water and form neutral solutions (pH=7)

Answer 1

fewer five atoms

Question 2

It is the general test for aldehydes and ketones

Answer 2

2,4 - DNP Test

Question 3

What is the reagent for 2,4-DNP test?

Answer 3

2,4 - dinitrophenylhydrazine

Question 4

What is the positive result of 2,4 - DNP Test?

Answer 4

Formation of orange-yellow or orange-red precipitate from a carbon-oxygen double bond in an aldehyde or ketone

Question 5

TRUE OR FALSE

Ketones are readily oxidized to carboxylic acids whereas Aldehydes cannot be readily oxidized under acidic conditions

Answer 5

FALSE; Aldehydes are readily oxidized while Ketones cannot be readily oxidized under acidic conditions

Question 6

What is the test for aldehydes where the reagent is Ammoniacal Silver Nitrate?

Answer 6

Tollen’s Test

Question 7

What is the positive result for Tollen’s Test?

Answer 7

Formation of elemental silver, accumulated onto the inner surface of the reaction vessel, producing silver mirror on the inner surface of the vessel

Question 8

It is test for aldehydes where the reagent is Fehling’s solution A (CuSO4) and Fehling’s solution B (sodium potassium tartrate or Rochelle salt and stong alkali - NaOH)

Answer 8

Fehling’s Test

Question 9

What is the positive result for Fehling’s Test?

Answer 9

Formation of red precipitate (cuprous oxide)

Question 10

It is a test for aldehydes where the reagent is 4-amino-5-mercapto-1,2,4-triazole (heterocyclic compound)

Answer 10

Purpald Test

Question 11

Purpald Test reacts with aldehydes to form a ____________?

Answer 11

Cyclic Derivative

Question 12

TRUE OR FALSE:

When react with the reagent, the cyclic derivative is then oxidized by exposure to air and forms an intensely colored (usually purple) product.

Answer 12

TRUE

Question 13

It is a test for aldehydes where the reagent is CrO3/H2SO4

Answer 13

Jones Test

Question 14

What is the positive result for Jones Test?

Answer 14

disappearance of orange color (Jones’ reagent) and appearance of greenish precipitate

Question 15

In Jones Test, Aldehydes are rapidly oxidized to __________?

Answer 15

Carboxylic Acids

Question 16

What is the reagent for Schiff’s Test?

Answer 16

Schiff’s Reagent

Question 17

What is the positive result for Schiff’s Test?

Answer 17

appearance of pink or magenta color

Question 18

It is a test for ketones where the reagent is m-dinitrobenzene

Answer 18

m-dinitrobenzene test

Question 19

What is the positive result for m-dinitrobenzene test?

Answer 19

appearance of violet color

Question 20

It is a test for ketones where the reagent is sodium nitroprusside in alkaline medium

Answer 20

Rothera’s Test

Question 21

What is the positive result for Rothera’s Test?

Answer 21

Appearance of red color complex

Question 22

It is a polyhydroxy aldehydes or ketones or substances that hydrolyze to yield polyhydroxy aldehydes and ketones

Answer 22

Carbohydrates

Question 23

What are the classifications of Carbohydrates?

Answer 23

1. Monosaccharides
2. Disaccharides
3. Polysaccharides

Question 24

It is a reduction test for carbohydrates

Answer 24

Benedict’s Test

Question 25

It free aldehyde or keto group in the reducing sugars reduce cupric hydroxide in alkaline medium to red colored cuprous oxide

Answer 25

Benedict’s Test

Question 26

depending on the concentration of sugars, _______________ is developed

Answer 26

yellow to green color

Question 27

What is the positive result for Benedict’s Test?

Answer 27

Formation of brick red precipitation

Question 28

All_____________ are reducing sugars as they all have a free reactive carbonyl group.

Answer 28

monosaccharides

Question 29

TRUE OR FALSE:

Some disaccharides, (i.e. reducing disaccharides) have exposed carbonyl groups but less reactive than monosaccharides.

Answer 29

TRUE

Question 30

What is the general test for the presence of the carbon-oxygen double bond?

Answer 30

2,4 - DNP Test

Question 31

2,4,-DNP Test

What are the ways to help identify the specific aldehyde/ketone?

Answer 31

• Recrystallization
• Purification
• MP Determination

Question 32

MULTIPLE CHOICE:

All of these are the complications of 2,4-DNP Test EXCEPT:

a. Some ketones give oils which will not solidify
b. Some allylic alcohols are oxidized by the reagent to aldehydes and ketones and give positive result
c. Some not pure alcohols may contain aldehyde or ketone impurities
d. The color usually develops in 5-15 secs

Answer 32

d. The color usually develops in 5-15 secs

Question 33

It is a test for acetaldehyde and methyl ketones where the reagent is I2/NaOH

Answer 33

Iodoform Test for Methyl Ketone

Question 34

What is the positive result for Iodoform Test for Methyl Ketone?

Answer 34

Formation of a yellow precipitate or suspension of iodoform and a distinct smell

Question 34

It is the reaction at the alpha carbon where a C-H bond on the alpha carbon to a carbonyl grop is more acidic than many other C-H bonds because reaction with base forms a resonance-stabilized enolate ion

Answer 34

Haloform Reaction

Question 35

____________ are nucleophiles, and so they react with electrophiles to form new bonds on alpha carbon.

Answer 35

Enolates

Question 36

Oxidation:

What is formed under alkaline condition?

Answer 36

Salt

Question 37

TRUE OR FALSE:

When oxidizing, ketones need a stronger oxidzing agent while aldehydes need mild oxidizing agent

Answer 37

TRUE

Question 38

What are the two complications on Tollen’s Test?

Answer 38

1. The tube must be clean and oil free if a silver mirror is to be observed
2. Aromatic Amine & some phenols are easily oxidized which give false positive results

Question 39

What are the complication in Jones Test?

Answer 39

Usually color develops in 5-15 secs