Parr Instrument 6200 - Manual (Page 63)

64
6200
Calorimeter Operating Instruction Manual
• 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.
Example:
(Percent Sulfur) x (Sample Mass) x
10 = milligrams of sulfur
(milligrams of sulfur) / (equivalent wt. of S
in H
2
SO
4
) = milliequivalents of H2SO4
Sulfur Multiplier is then 10 / equivalent wt.
of S in H
2
SO
4
or 10/16.03 = 0.6238
e
1
is the nitric acid portion of the total acid
correction.
e
2
is the sulfuric acid portion of the total
acid correction.
e
1
+ e
2
is the total bomb acid correction.
Calculation for e
1
when entered acid value
is total acid:
[((total acid) (acid mult))-(percent sulfur)
(sample mass) (sulfur mult) ] (heat of
formation of HNO
3
)
Total acid milliequivalents - milliequivalents
of H
2
SO
4
= milliequivalents of HNO
3
.
(milliequivalents of HNO
3
) (heat of formation
of HNO
3
) = heat (in calories) due to HNO
3
produced.
Calculation for e
1
when entered acid value
is nitric acid only:
(nitric acid) (acid multiplier) (heat of
formation of HNO
3
).
Calculation of e
2
when entered sulfur value
is % sulfur:
e
2
= (percent sulfur) (sample mass) (sulfur
multiplier) (heat of formation of H
2
SO
4
).
Acid and
Sulfur
Corrections
B-4
APPENDIX B