Ball State University
Chemistry Analysis
CHEM 225
Laboratory Report
Experiment No. 6
Experiment: Kjeldahl Analysis of Blood and Nitrogen
Name: Haley N. Snyder
Date: 02/20/2014
I.
Introduction
This lab of blood analysis consisted of acid-base titrations. Three titrations were done using indicator
solutions as well as certain specified weights of other substances to make the sample blood solution
titration-ready for the lab procedures. Throughout this experiment, the analysis of Nitrogen within a
sample of blood was done. Although Nitrogen is a very difficult element to analyze, the process was
done with precision and accuracy. The procedures completed within the lab were bio-chemistry
based and founded by Kjeldahl, an organic chemist. In more general terms, the analysis of Nitrogen
was performed within the presence of a dense matrix.
II.
Procedure
The following procedures were utilized within the lad with the variation of the exclusion of
performing the procedures within the Macro Method: G-6 Semi-Micro Method – Digestion Phase,
Distillation Phase and Titration Phase.
III.
Equipment and Reagents
The following equipment and reagents were used within the lab experiment other than those tools
held within the general equipment drawers assigned: unknown dried blood sample (B), Sucrose
(C_12_H_22_O_11), ungummed cigarette paper, Sodium Sulfate (Na_2_SO_4_) reagent grade solid,
Sulfuric Acid (1:1), Hengar catalyst granules, Sodium Hydroxide (NaOH) reagent grade flasks or
pellets, Boric Acid (HBO_2_) reagent grade solid, granulated or mossy zinc metal, standard N/10 or
N/100 H_2_SO_4_ and Methyl Purple indicator solution.
IV.
Data, Graphs and Statistics
The table below represents all weights and data collected while performing each procedure:
Flask Description g Blood Sample (B) Na_2_SO_4 (g)
23
0.0301 g
1.501 g
3
0.0304 g
1.530 g
D2
0.0302 g
1.503 g
Weight of Boric Acid in receiving beaker: 4.03 g HB
NaOH Pellets (g)
5.101 g
5.140 g
5.010 g
ml Burette (H^+)
27.7 ml
28.5 ml
28.1 ml
The table below represents the calculated percent of Nitrogen present within each blood sample:
g Blood Sample (B)
0.0301 g
0.0304 g
0.0302 g
Mean: 17.92% N
Standard Deviation: 0.1657
Q-Test: 0.576 < 0.941 (data must be retained)
%N Present in Blood Sample (B)
17.75% N
18.08% N
17.94% N
V.
Discussion
The analysis of nitrogen within a matrix presents itself to many obstacles in retaining appropriate
data and results. Blood is very difficult to analyze due to the fact that it is so complex and so intense
with other dense materials contained within it, which causes the analysis of the elements within it
to be difficult as well. Nitrogen is considered an inner gas and does not necessarily do anything
drastic to reveal itself. Considering nitrogen makes up about 75% of our world, it is difficult to
analyze because if its abundance in preservatives, humans, foods, animals, etc.
The main point if the blood analysis lab was analyze the nitrogen present which is done by either the
Macro-Method or the Semi-Micro Method which was founded by Kjeldahl, an organic chemist.
Because the Macro-Method involves the analysis of large quantities of certain substances, within
this specific lab procedure, the Semi-Micro Method was utilized due to the small quantities of
sample analyzed.
Because of the small quantities of the blood sample used, there was a large possible margin of error:
the method of weighing out a 0.0300 g sample of the dried cow blood was done by placing cigarette
paper on the scale, zeroing that mass out and then placing the sample on the paper instead of a
weighing boat. This method was used because of the forces of static electricity between the plastic
weighing boat and the blood sample. If any of the sample was lost and/or dropped off of that
weighing boat then the experiment would have been ruined. However, a large portion of that error
was avoided by using the rolling paper instead, but when transferring the weighed sample of blood
from the scale to the flask itself presented error as well. When crumpling the rolling paper onto
itself to entrap the sample, a small percentage of the sample was liable to either fall out or bounce
off of the paper from the vibrations of the crackling paper. This minor loss of sample could have led
to error within the calculations later in the lab.
When analyzing the digestion phase of life within a human, we review over what aspects make
digestion happen: HCl acid, enzymes, heat (body heat), time (5 hours) and excretion (urine and
feces). Comparing digestion of food in humans to the digestion of substances in the lab procedure,
we review over similar aspects in lab that serve as a mere replacement of those in the human body:
H_2_SO_4 acid, Hengar crystals (catalyst), heat (boiling the solution prepared), time (5-10 minutes
for color change) and digestion of the substance 100%. Hypothetically, humans should not be
excreting feces. If humans did not have a large intestine and digested the substances put into the
body 100%, only urine would be excreted. Within the lab procedure, a type of process similar to this
is expressed.
When the blood solution is prepared, heating of the solution for five to ten minutes is vital in order
to reach the desired color change to the yellowish-clear pigment after the appearance of a black,
think substance is boiled through. Precautionary measures must have been taken in order to ensure
that no glass-wear was broken or cracked. Glassware utilized within the experiment was extremely
sensitive to heat and had to be watched closely. If glass were to be broken within any part of the
procedure, the sample contained within it would have been ruined and not reusable or even able to
be recycled for later experiments/procedures. Due to the fragility of the flasks, placing them within
beakers to hold them in place was done to ensure safety both of the glassware as well as the
analyzers within the experiment.
When cleaning the flasks before proceeding to the rest of the experiment, thorough cleaning is vital.
If there is presence of other substances within the flask, the digestion phase could have possibly
been altered or varied due to whatever extra substance was present. Analyzing the flasks for hairline cracks as well as star-crack was also important before performing the lab due to the risk of
breakage and loss of sample obtained.
When preparing for the heating process, placing the flask in the appropriate position on the Kjeldahl
Digestion Rack is important for efficient heating of the solution in the flask. For efficient heating,
placing the flask under the suction hole closest to the hoes allows for proper of gas extraction into
the drain so the laboratory room does not fill up with toxic gaseous air.
Setting up the distillation apparatus provides area for error as well. When connecting the few parts
of the apparatus, making sure the plugs and glass are secure is vital. If the stoppers are not tightly
secure within the opening of the glassware then gas is able to leak out which prevents the digestion
and evaporation of the solution from the flask to the receiving beaker. This error causes error within
the following procedures of titration and volumetric measurements within the burette.
While heating the solution in the flask over the Bunsen burner, controlling the temperature is crucial
due to the need to moderate the amount of bubbles created in the receiving flask. If the bubbles are
produced too fast then the solution is unable to trap the gas accurately which defeats the purpose
of the lab results in the end after the calculations. If the temperature is dropped then the pressure
and volume vary which in turn ruins the experiment. Once the experiment is ruined it is impossible
to make up.
One last error possible within this experiment is the possibility of the substance not digesting 100%
which then leads to inaccurate results and conclusions toward the end of the lab procedure.
VI.
References
There were no outside references used within the lab experiment.