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Certification of national research center for certified reference materials (NRCCRM, Beijing) thermochemical standard benzoic acid
M-2454(N) J. Chem. Thermodynamics 1990,22,
319-320
Note Certification of National Research Center for Certified Reference Materials (N RCCRM, Beijing) Thermochemical Standard benzoic acid LI SHAOFENG, and HE XIHENG
GAO PEIZHEN,
YU XIUHUI,
LI XINGYA,
National Research Center for CertiJied Reference Materials, 7, District II, Heping Street, Beijing 100013, People’s Republic of China (Received 14 December 1989)
The National Research Center for Certified Reference Materials (NRCCRM) in Beijing is the only research institute in China with the equipment and technique for electrical calibration of a bomb calorimeter with the absolute accuracy and precision required for measuring the calorific values of samples of benzoic acid. The certification of standard benzoic acid samples at this center began in 1968, and a certificate value of (26436.0& 5.8) J *g-’ was given in 1972. Recently the apparatus has been redesigned and improved, and a determination of the energy of combustion of standard benzoic acid in terms of electrical units has been made. The sample of benzoic acid was refined by fractional freezing to give a material of high homogeneity and purity. Freezing-temperature measurements indicated a purity of about 99.99, moles per cent. The static-bomb calorimeter was essentially similar to those described by Coops et al.“* 2’ and Gundry et al.w The calorimeter system was submerged in a thermostat bath controlled at (296.150f0.001) K by a semiconductor controller. The electrical calibration measuring circuit was similar to that described by Coops et aLc4)All the instruments and standards were calibrated by the National Institute of Metrology in Beijing. As reported by Coops et al.,(4) the calibration of the calorimeter was made with 1 cm3 of water, cotton-thread ignition fuse, platinum ignition wire, and oxygen at 3.04 MPa in the bomb which had an internal volume of 0.280 dm3. From nine calibrations the values of the energy equivalent E,i/(J. K-‘) of the standard initial calorimeter system were 13395.6, 13396.8, 13392.8, 13395.6, 13392.6, 13394.4, 13393.5, 13392.6, and 13396.3: giving a mean and its standard deviation of (13394.5 kO.55). Samples were ignited in oxygen at 3.04 MPa and 1 cm3 of water was added to the bomb. For the cotton-thread fuse -Acuo = 1703 J.g-‘. AU(HN0,) was based on - 59.7 kJ mol- ’ for the standard molar energy of formation of 0.1 mol. dm3 HNO, 0021-9614/90/030319+02
$02.00/O
0 1990 Academic Press Limited
NOTE
320
TABLE 1. Energy of combustion of benzoic acid at 296.15 K
m,lg
AS/K
1.14447 1.14456 1.14496 1.14474 1.14439 1.14533 1.14536 1.14269 1.14354
2.26247 2.26585 2.26523 2.26421 2.26264 2.26560 2.26497 2.26068 2.26160
-AU/J
- WJ
-Au,/(J.g-‘)
52.0 80.5 85.7 67.1 54.5 66.1 63.0 67.5 64.1
26436.5 26449.1 26428.0 26437.6 26438.2 26440.9 26435.6 26433.1 26437.2 26437.4 +1.9
30307.8 30353.1 30344.7 30331.9 30310.1 30349.7 30341.3 30283.8 30296.1
mean: standard deviation of mean:
from N,, 02, and H,O(l).“’ The electrical ignition energy AU(ign) was calculated from the potential change across a 7007 uF capacitor when discharged through the platinum ignition wire. The results of the combustion measurements are given in table 1 where m, denotes the mass of benzoic acid, A0 the corrected temperature rise, -AU the total energy change, -Xq the sum of the energies involved in the formation of nitric acid, combustion of cotton-thread fuse, and electrical ignition, and - A,u the specific energy of combustion of benzoic acid referred to 296.15 K. The specific energy of combustion under standard bomb conditions@’ was calculated from the mean value of -A,u to be (26433.4f 1.9) J.g--‘. Taking into account the uncertainties arising from application of corrections and calibrations of instruments and standards, the total uncertainty calculated from the standard deviation of the mean of energy-equivalent determinations and the standard deviation of the mean of the combustion measurements was 0.007 per cent. This was doubled for the certificate value: -Au, = (26433.4 +4.0) J . g- ‘, for this batch of NRCCRM Thermochemical Standard benzoic acid which has been approved by the State Bureau of Technology Inspection, The People’s Republic of China, as a certified reference material for combustion calorimetry. REFERENCES 1. Coops, J.; Nes. K. van; Kentee, A.; Dienske, J. W. Rec. Trav. Chim. Pays Bas 1947, 66, 113 2. Coops, J.: Nes, K. van Rec. Trav. Chim. Pays Bas 1947, 66, 131. 3. Gundry, H. A.; Harrop, D.; Head, A. J.; Lewis, G. B. J. Chem. Thermodynamics 1969, 1, 321-332. 4. Coops, J.; Jessup, R. S.; Nes, K. van Experimental Thermochemistry, F. D. Rossini, editor. interscience: New York. 1956, ch. 3. 5. The NBS Tables of Chemical Thermodynamic Properties, J. Phys. Chem. Ref. Data 1982, 11, supplement No. 2. 6. Standard bomb conditions: combustion in oxygen at 3.04 MPa where m, (sample mass) and m, (mass of water added to the bomb) are related to the internal volume, V, of the bomb by m,/g = m,/g = 3 V/dm’, and the combustion reaction is referred to 298.15 K.
319-320
Note Certification of National Research Center for Certified Reference Materials (N RCCRM, Beijing) Thermochemical Standard benzoic acid LI SHAOFENG, and HE XIHENG
GAO PEIZHEN,
YU XIUHUI,
LI XINGYA,
National Research Center for CertiJied Reference Materials, 7, District II, Heping Street, Beijing 100013, People’s Republic of China (Received 14 December 1989)
The National Research Center for Certified Reference Materials (NRCCRM) in Beijing is the only research institute in China with the equipment and technique for electrical calibration of a bomb calorimeter with the absolute accuracy and precision required for measuring the calorific values of samples of benzoic acid. The certification of standard benzoic acid samples at this center began in 1968, and a certificate value of (26436.0& 5.8) J *g-’ was given in 1972. Recently the apparatus has been redesigned and improved, and a determination of the energy of combustion of standard benzoic acid in terms of electrical units has been made. The sample of benzoic acid was refined by fractional freezing to give a material of high homogeneity and purity. Freezing-temperature measurements indicated a purity of about 99.99, moles per cent. The static-bomb calorimeter was essentially similar to those described by Coops et al.“* 2’ and Gundry et al.w The calorimeter system was submerged in a thermostat bath controlled at (296.150f0.001) K by a semiconductor controller. The electrical calibration measuring circuit was similar to that described by Coops et aLc4)All the instruments and standards were calibrated by the National Institute of Metrology in Beijing. As reported by Coops et al.,(4) the calibration of the calorimeter was made with 1 cm3 of water, cotton-thread ignition fuse, platinum ignition wire, and oxygen at 3.04 MPa in the bomb which had an internal volume of 0.280 dm3. From nine calibrations the values of the energy equivalent E,i/(J. K-‘) of the standard initial calorimeter system were 13395.6, 13396.8, 13392.8, 13395.6, 13392.6, 13394.4, 13393.5, 13392.6, and 13396.3: giving a mean and its standard deviation of (13394.5 kO.55). Samples were ignited in oxygen at 3.04 MPa and 1 cm3 of water was added to the bomb. For the cotton-thread fuse -Acuo = 1703 J.g-‘. AU(HN0,) was based on - 59.7 kJ mol- ’ for the standard molar energy of formation of 0.1 mol. dm3 HNO, 0021-9614/90/030319+02
$02.00/O
0 1990 Academic Press Limited
NOTE
320
TABLE 1. Energy of combustion of benzoic acid at 296.15 K
m,lg
AS/K
1.14447 1.14456 1.14496 1.14474 1.14439 1.14533 1.14536 1.14269 1.14354
2.26247 2.26585 2.26523 2.26421 2.26264 2.26560 2.26497 2.26068 2.26160
-AU/J
- WJ
-Au,/(J.g-‘)
52.0 80.5 85.7 67.1 54.5 66.1 63.0 67.5 64.1
26436.5 26449.1 26428.0 26437.6 26438.2 26440.9 26435.6 26433.1 26437.2 26437.4 +1.9
30307.8 30353.1 30344.7 30331.9 30310.1 30349.7 30341.3 30283.8 30296.1
mean: standard deviation of mean:
from N,, 02, and H,O(l).“’ The electrical ignition energy AU(ign) was calculated from the potential change across a 7007 uF capacitor when discharged through the platinum ignition wire. The results of the combustion measurements are given in table 1 where m, denotes the mass of benzoic acid, A0 the corrected temperature rise, -AU the total energy change, -Xq the sum of the energies involved in the formation of nitric acid, combustion of cotton-thread fuse, and electrical ignition, and - A,u the specific energy of combustion of benzoic acid referred to 296.15 K. The specific energy of combustion under standard bomb conditions@’ was calculated from the mean value of -A,u to be (26433.4f 1.9) J.g--‘. Taking into account the uncertainties arising from application of corrections and calibrations of instruments and standards, the total uncertainty calculated from the standard deviation of the mean of energy-equivalent determinations and the standard deviation of the mean of the combustion measurements was 0.007 per cent. This was doubled for the certificate value: -Au, = (26433.4 +4.0) J . g- ‘, for this batch of NRCCRM Thermochemical Standard benzoic acid which has been approved by the State Bureau of Technology Inspection, The People’s Republic of China, as a certified reference material for combustion calorimetry. REFERENCES 1. Coops, J.; Nes. K. van; Kentee, A.; Dienske, J. W. Rec. Trav. Chim. Pays Bas 1947, 66, 113 2. Coops, J.: Nes, K. van Rec. Trav. Chim. Pays Bas 1947, 66, 131. 3. Gundry, H. A.; Harrop, D.; Head, A. J.; Lewis, G. B. J. Chem. Thermodynamics 1969, 1, 321-332. 4. Coops, J.; Jessup, R. S.; Nes, K. van Experimental Thermochemistry, F. D. Rossini, editor. interscience: New York. 1956, ch. 3. 5. The NBS Tables of Chemical Thermodynamic Properties, J. Phys. Chem. Ref. Data 1982, 11, supplement No. 2. 6. Standard bomb conditions: combustion in oxygen at 3.04 MPa where m, (sample mass) and m, (mass of water added to the bomb) are related to the internal volume, V, of the bomb by m,/g = m,/g = 3 V/dm’, and the combustion reaction is referred to 298.15 K.