Activity No. 12

Question 1

carboxylic acids are prepared by _____

Answer 1

the oxidation of compounds whose molecules contain certain functional groups

Question 2

they can be oxidized directly to carboxylic acid using KMnO4 as oxidizing agent

Answer 2

Primary alcohols, aldehydes, some alkenes and methyl ketones

Question 3

A carboxylic acid can also be prepared from the self-oxidation and reduction of ______

Answer 3

aldehydes that do not have alpha hydrogens (e.g. formaldehyde and benzaldehyde)

Question 4

Self oxidation and reduction of aldehydes that do not have alpha hydrogens. This reaction is called the _________

Answer 4

Cannizzaro reaction

Question 5

Cannizzaro rxn is (acid- , base-) catalyzed

Answer 5

base-catalyzed

Question 6

it is preferred over oxidation of KMnO4 in synthesizing benzoic acid

Answer 6

Cannizzaro method (reaction)

Question 7

why does the oxidation of with KMnO4 is not preferred in synthesizing benzoic acid?

Answer 7

Since it has a by-product, MnO2, that is highly insoluble and is often found in very finely divided form which can cause for a slower filtration process. Thus, there is then a need to coagulate the MnO2 into larger, more easily filtered particles for better separation from the desired product

Question 8

what is the starting material (activity #10)

Answer 8

benzaldehyde

Question 9

what will be the product in the cannizzaro method

Answer 9

sodium benzoate

Question 10

how will you then obtain the desired product, benzoic acid?

Answer 10

by acidifying the obtained sodium benzoate

Question 11

what reagents were used for the characterization of the product? (act #12)

Answer 11

Schiff reagent
FeCl3

Question 12

this reagent is used to charecterize benzaldehyde from benzoic acid as it is highly sensitive test for aldehydes

Answer 12

Schiff reagent

Question 13

In Schiff’s test, benzaldehyde reacts with the _____________ to form a characteristic _______ color, while benzoic acid gives a (positive/negative) test.

Answer 13

fuschin-aldehyde reagent
magenta
negative

Question 14

This heavy metal reagent used in this experiment characterizes benzoic acid

Answer 14

FeCl3

Question 15

The rxn with FeCl3 results in the ____________ which is used as basis for specific tests for _______ and _______. The salt of _______ forms _________ w/ FeCl3

Answer 15

formation of salts
benzoic acid
acetic acid
bezoic acid
insoluble colored compounds

Question 16

PROCEDURE:
Step 1(activity #12)

Answer 16

dissolve 1.96g of solid KOH in 2mL distilled water in a 25ml erlenmeyer flask, by swirling in a 100ml beaker containing tap water. After the KOH has dissolved, cool the mixture to room temp by adding ice into the beaker

Question 17

PROCEDURE:
Step 2 (acti #12)

Answer 17

add the prepared KOH solution in a 25ml round-bottomed flask containing 0.07 mole of benzaldehyde. Stopper the flask and shake vigorously until an emulsion is formed.

Question 18

PROCEDURE:
Step 3 (act #10)

Answer 18

To this mixture, add 1ml water, stopper and shake. if the crystals obtained do nit dissolve, add little water, break up the soild mass w/ a glass rod, stopper and shake again. repeat until all the crystals are dissolved

Question 19

PROCEDURE:
Step 4 (activity #12)

Answer 19

Pour the resulting solution into a separatory funnel. Wash this solution 3 times w/ 10mL portions of ether. Shake gently after each addition to avoid forming an emulsion. Draw out the aqueous layer and drain the upper layer into another container. Return the lower layer that contains the product into the separatory funnel and repeat tge process wjth the remaining portions of ether

Question 20

PROCEDURE:
Step 5

Answer 20

pour the alkaline lower layer (w/ vigorous stirring) into a beaker containing 5ml concentrated HCl, 4ml water and about 5 g crushed ice. Cool the mixture in an ice bath and collect the benzoic acid crystals. Recrystallize the crystals from approx. 50ml of hot water and air-dry

Question 21

Performing the Schiff’s test:

Answer 21

place 0.5 ml of benzaldehyde and 0.5 ml benzoic acid solution in separate test tubes. Add a drop of Schiff’s reagent to each test tube

Question 22

Performing FeCl3 test

Answer 22

In a test tube containing the remaining benzoic acid, add 10% NH4OH until slightly basic to litmus. Boil off excess NH3 and add 2 drops of FeCl3 solution. The same thing was done using 1.5 ml benzaldehyde as the test solution.

Question 23

what is the limiting reagent in this experiment (activity #12)

Answer 23

benzaldehyde

Question 24

melting point of the product, benzoic acid (observed)

Answer 24

115°C - 118°C

Question 25

Test Compound: Benzaldehyde

(a)Schiff’s Test Result:
(b)FeCl3 Test Result:

Answer 25

(a) magenta colored solution (+)
(b) no rxn (-)

Question 26

Test Compound: Benzoic acid

(a) Schiff’s Test Result:
(b)FeCl3 Test Result:

Answer 26

(a) no reaction (-)
(b) buff colored solution and precipitate was formed (+)

Question 27

how would propionaldehyde react w/ KOH solution under the conditions of this experiment?

Answer 27

the cannizzaro rnx is the disproportionation in concentrated base of an aldehyde lacking an alpha hydrogen atom to form a carboxylic acid and primary alcohol. Since propionaldehyde has 2 alpha hydrogen, it will not undergo rxn under the conditions of this experiment

Question 28

in the separatory funnel which layer is aqueous?

Answer 28

lower layer

Question 29

in which layer contains the product

Answer 29

lower layer

Question 30

title of activity #12

Answer 30

Synthesis of Benzoic acid