Parr Instrument 6200 - Manual (Page 53)

Calculations
6200 B
w w w . p a r r i n s t . c o m 51
Thermochemical Calculation Details
Traditionally, standard solutions and procedures
have been established to simplify the calculations
related to the thermochemical corrections. The 6200
Calorimeter has been programmed to permit the
user to use standard solutions and units which are
most convenient, since the microprocessor can
easily apply any conversion factors required.
Acid and Sulfur Corrections
• Total acid is the amount of base required to
titrate the bomb washings (milliliters).
• Nitric acid is that portion of the total acid in the
bomb washings that result when the nitrogen
in the air that is trapped in the bomb is burned
at high pressure. Since this nitric acid does not
result from the sample, and the combustion
conditions are reasonably constant from test
to test, the amount of nitric acid formed is also
constant.
• Acid multiplier is multiplied by the user
entered acid value to arrive at the number of
milliequivalents of acid. This value is normally
the concentration (normality) of the base in
equivalents per liter (N).
• Percent sulfur is the concentration of sulfur in
the sample (weight %).
• Molecular weight of sulfur is 32.06.
• Equivalent weight of sulfur in H
2
SO
4
is 16.03
(one half of the molecular weight).
• Heat of formation of nitric acid is 14.1 calories/
milliequivalent.
• Heat of formation of sulfuric acid (from SO
2
) is
36.1 calories/milliequivalent.
• Sample mass is the mass of sample burned in
the bomb (grams).
• Sulfur multiplier is multiplied by the product of
the user entered sulfur value and the sample
mass to arrive at the number of milliequivalents
of sulfuric acid in the bomb washings.
Sulfur Correction:
e2 = (percent sulfur)(sample mass)(sulfur
multiplier)(heat of formation of H
2
SO
4
).
Acid Correction:
In the 6200 there are a number of settings for the
acid correction.
e1 is the nitric acid portion of the correction.
Fixed HNO
3
: The Acid Correction is a fixed value set
by the operator.
The calculation is:
e1 = (nitric acid value)(acid multiplier)(heat of
formation of nitric acid)
For an 1108P style bomb, the default nitric acid value
is 10 and acid multiplier is .0709. The heat of forma-
tion of nitric acid is 14.1 calories/milliequivalent so
the calculation is:
e1 = (10)(.0709)(14.1) or e1 = 9.9969 (rounds to 10)
When the Acid Correction is set to Fixed HNO
3
the
value is considered a final value and the operator is
not prompted for an acid value when reporting the
results.
Entered HNO
3
: The Acid Correction is entered by the
operator when reporting the results.
The calculation is the same as Fixed HNO
3
above.
The value listed on the Acid Correction button is
used for preliminary calculations. When finalizing
the report the operator will be prompted for the acid
value.
Fixed Total: The Acid Correction represents the total
base required to titrate the bomb washings (in mil-
liliters). This includes both nitric and sulfuric acid.
The correction is a fixed value set by the operator.
The calculation is:
e1 = [((total acid)(acid multiplier)) – (% sulfur)
(sample mass)(sulfur multiplier)](heat of
formation of nitric acid)