Lab - Determination of Nitrogen/Crude Protein

Question 1

What method was used in the experiment?

Answer 1

Kjeldahl technique

Question 2

To be more specific, the ____ modification of the Kjeldahl technique was used

Answer 2

Winkler

Question 3

three phases of the Winkler modification of the Kjeldahl technique

Answer 3

digestion with acid
distillation to release the ammonia
titration with standard sulfuric acid

Question 4

digestion phase involves decomposition of organic nitrogen compounds c/o of which acid?
A. hydrochloric
B. boric
C. sulfuric
D. muriatic

Answer 4

C

Question 5

in acid digestion phase, organic C and H become

Answer 5

CO2 and H2O

Question 6

in acid digestion phase, H2SO4 reduced into SO2. SO2 reduces nitrogenous material into __

Answer 6

ammonia

Question 7

in acid digestion, reduction in time is done y adding K2SO4 or Na2SO4. Why?

Answer 7

they may raise the boiling point of the mixture

Question 8

in the distillation stage to release ammonia, what acid is used?
A. hydrochloric
B. boric
C. sulfuric
D. muriatic

Answer 8

B

Question 9

protein is assumed to have __% of Nitrogen

Answer 9

16

Question 10

What indicator was used in the experiment?
A. phenolphthalein
B. methylene red
C. bromcresol-green

Answer 10

C

Question 11

What distillation apparatus was used?

Answer 11

Markham distillation apparatus

Question 12

Methods for determining nitrogen & crude protein are directly based on
A. Speed of result delivery
B. Presence of Functional groups in the molecule
C. Both A & B

Answer 12

B

Question 13

The ultimate reference method for determining the concentration of protein is the ___

Answer 13

Analysis of Nitrogen content

Question 14

In titration stage of Winkler modif of Kjeldahl technique, why is boric acid added?

Answer 14

To trap ammonia; it is too weak to affect H+ concentration