Most of the earliest determinations of CO2 concentrations were by chemical analysis of dried atmospheric air through absorption by alkalis such as Ba(OH)2 and subsequent titration. A known volume of air was usually dried by passing it through U-tubes of concentrated H2SO4 before entering the main flask where the CO2 was to be absorbed by the alkali.
Hlasiwetz (1856) Ueber Kohlensäure-Bestimmungen der Atmosphärischen Luft (link given below) mentions the possibility that some of the CO2 might be absorbed by the H2SO4 before entering the flask; this would obviously make the determination of the CO2 concentration unreliably low.
I have consulted the IUPAC-NIST Solubility Database http://srdata.nist.gov/solubility/ , entered the search menu on the left-hand side, and then chose the two system component sub-menu http://srdata.nist.gov/solubility/comp2MolFmls.aspx , entering the two search strings: CO2 and H2SO4.
The result http://srdata.nist.gov/solubility/sol_2casno.aspx?STR1=CO2&STR2=H2SO4&OPTION=MOL gives seven possible hits (click on the "system", not on the CAS No.), but two of them also involve Na2SO4, and so are probably not relevant. The remaining five are the results of five different investigations carried out between 1877 and 1957, but I cannot understand any of them (my knowledge of the topic/terminology is insufficient at this level!)
Can someone help me to understand what they mean? Is CO2 likely to be absorbed into concentrated H2SO4 from air at typical ambient temperatures and humidities, and if so, to what extent? How might this absorption vary with different conditions (temp., pressure, etc) How might this have compromised the accuracy of the determinations of [CO2]?
http://books.google.co.uk/books?hl=en&lr=&id=gJo5AAAAcAAJ&oi=fnd&pg=PA1&dq=hlasiwetz+kohlensaurebestimmungen&ots=eft7yDl2pE&sig=p7QuBnmSNsYaD0w_u-AyPw6qC0Y#v=onepage&q&f=false
The NIST site lists water as a component of all the systems in the solubility evaluation. There are no entries for just CO2 and H2SO4. I would be a bit surprised if sulfuric acid dissolved a significant amount of CO2. CO2 is the anhydride of carbonic acid. When it dissolves in water, for example, it forms H2CO3 in the solution. A strong dehydrating agent like concentrated sulfuric acid will dehydrate H2CO3 leaving behind CO2. If you want to check experimentally for solubility of CO2 in concentrated H2SO4 you could try using an alternative dehydrating agent like phosphorus pentoxide or magnesiun perchlorate. If this consistently gives you a higher CO2 concentration you might suspect the sulfuric acid. The downside of using H2SO4 over a long period would be that if it absorbs a significant amount of water from the air it will get somewhat diluted and that could cause trouble so the H2SO4 needs to be concentrated and fresh.
Thank you for this answer, John. However, it doesn't seem to concord with Hlasiwetz's paper (see the attachment in my original question). In particular in his paper ...
1. The absorption tubes, instead of gaining weight, sometimes lost weight.
http://books.google.co.uk/books?id=gJo5AAAAcAAJ&pg=PA6&img=1&zoom=3&hl=en&sig=ACfU3U06-3_JRXrl9HVl47lGvdUZjH-XJg&ci=172%2C1045%2C727%2C307&edge=0
2. One possible source of errors is that some of the CO2 might be absorbed by the conc. H2SO4
http://books.google.co.uk/books?id=gJo5AAAAcAAJ&pg=PA7&img=1&zoom=3&hl=en&sig=ACfU3U0WJwH3YKYGt1741OHgAmJjmee8kA&ci=74%2C255%2C723%2C120&edge=0
3. In control experiments on the possible absorption of dried CO2 by conc. H2SO4, up to 7 to 10% of the CO2 could be absorbed by the acid.
http://books.google.co.uk/books?id=gJo5AAAAcAAJ&pg=PA7&img=1&zoom=3&hl=en&sig=ACfU3U0WJwH3YKYGt1741OHgAmJjmee8kA&ci=73%2C562%2C705%2C210&edge=0
4. When he carried out pairs of experiments, using Conc. H2SO4 in one set of apparatus, and anhyd. CaCl2 in the other, he found no consistency in the results.
http://books.google.co.uk/books?id=gJo5AAAAcAAJ&pg=PA11&img=1&zoom=3&hl=en&sig=ACfU3U0wLO-SQPRWoYEqxoWcE-TcNcpK7Q&ci=114%2C218%2C712%2C404&edge=0
Was this merely because he was a bad experimenter?
Other investigators since Hlasiwetz who used chemical methods of [CO2] determination do not appear to have answered this potential problem. But, in order to have a reasonable reply to the late E-G Beck, a prominent critic of current ideas on anthropogenic global warming, I feel that it is necessary to deal with this question of CO2 and conc. H2SO4.
Dr. Mudge- This is an interesting problem. It is important in many reasons. The best that I found was in the literature for anaesthetics: the Ostwald Coefficient (lambda) is a measure of the number of mL of solvent needed to dissolve one mL of gas. In this case, you can see that for samples prepared it is somewhat variable but all around 1 mL solvent per mL CO2. (samples measured ranged from pure water to conc. sulfuric acid). What does this mean?
Probably not much. If you have dried your sample, you don't worry about changing the concentration of the solution. You can then just lookup or calculate the expected solubility and correct for this or run some calibration curves. (One of the reports was nice in that they were able to use 14C labelled CO2!)
I would wonder about saturation effects: is there anything besides "air" in the sample of CO2? How could this impact solubility of CO2 in the sample?
Since this work was done in the 1800's, they probably weren't concerned about issues in atmospheric chemistry, global warming, etc.--they were seeking to determine a reaction mechanism or the carbonate content of minerals (i.e. large amounts of CO2 evolved). This predated the periodic table, so the science of chemistry was young (but not unsophisticated!!!)
[As an aside, I'll note that my appreciation for sulfuric acid was quite low until I took time to understand where it came from, how it is made, and the reasons that make it one of the top commodity chemicals in the world--every year]
The background Hlasiwetz gives for his investigation is the peculiar climatic conditions of his place of residence (Innsbruck), and whether they have any connection with the CO2 content of the atmosphere, in particular any link with the notorious South winds that prevail at some times of year. So he was certainly trying to determine [CO2] at typical levels in the air - around 280 ppm - rather than at any higher concentrations.
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