Editing Gravimetric analysis (section)

=== Types of volatilization methods ===
In volatilization methods, removal of the analyte involves separation by heating or chemically decomposing a volatile sample at a suitable temperature.<ref name=":0" /><ref>{{Cite web |date=January 8, 2017 |title=Introduction to gravimetric analysis |url=https://www.khanacademy.org/ |url-status=live |archive-url=https://web.archive.org/web/20190801125426/https://www.khanacademy.org/ |archive-date=August 1, 2019 |access-date=January 8, 2017}}</ref> In other words, thermal or chemical energy is used to precipitate a volatile species.<ref>{{Cite web |date=January 8, 2017 |title=Gravimetric Methods of Analysis |url=https://www.emu.edu.tr/mugarip/chem247/lectureppt/c12%20gravimetric%20analysis.pdf |url-status=dead |archive-url=https://web.archive.org/web/20171118061918/https://www.emu.edu.tr/mugarip/chem247/lectureppt/c12%20gravimetric%20analysis.pdf |archive-date=November 18, 2017 |access-date=January 8, 2017}}</ref> For example, the water content of a compound can be determined by vaporizing the water using thermal energy (heat). Heat can also be used, if oxygen is present, for combustion to isolate the suspect species and obtain the desired results.

The two most common gravimetric methods using volatilization are those for water and carbon dioxide.<ref name=":0" /> An example of this method is the isolation of sodium hydrogen bicarbonate (the main ingredient in most antacid tablets) from a mixture of carbonate and bicarbonate.<ref name=":0" />  The total amount of this analyte, in whatever form, is obtained by addition of an excess of dilute [[sulfuric acid]] to the analyte in solution.

In this reaction, nitrogen gas is introduced through a tube into the flask which contains the solution. As it passes through, it gently bubbles. The gas then exits, first passing a drying agent (here CaSO<sub>4</sub>, the common desiccant ''Drierite''). It then passes a mixture of the drying agent ''and'' sodium hydroxide which lies on asbestos or ''Ascarite II'', a non-fibrous silicate containing sodium hydroxide.<ref>{{Cite book |last1=Skoog |first1=Douglas A |title=Fundamentals of Analytical Chemistry |last2=West |first2=Donald M |last3=Holler |first3=F James |publisher=Saunders College Publishing and Harcourt Brace |year=1995 |edition=Seventh |location=Fort Worth |pages=96–97 |chapter=5.6 |lccn=95-067683}}</ref> The mass of the carbon dioxide is obtained by measuring the increase in mass of this absorbent.<ref name=":0" />  This is performed by measuring the difference in weight of the tube in which the ascarite contained before and after the procedure.

The calcium sulfate (CaSO<sub>4</sub>) in the tube retains carbon dioxide selectively as it's heated, and thereby, removed from the solution. The drying agent absorbs any aerosolized water and/or water vapor (reaction 3.). The mix of the drying agent and NaOH absorbs the CO<sub>2</sub> and any water that may have been produced as a result of the absorption of the NaOH (reaction 4.).<ref name=":2">{{Cite web |date=January 8, 2017 |title=Section 3-2: Volatilization methods |url=https://www.csudh.edu/oliver/che230/textbook/ch03.htm |url-status=live |archive-url=https://web.archive.org/web/20161125160038/http://csudh.edu/oliver/che230/textbook/ch03.htm/ |archive-date=November 25, 2016 |access-date=January 8, 2017}}</ref>

The reactions are:

Reaction 3 - absorption of water

NaHCO<sub>3</sub><small>(aq)</small> + H<sub>2</sub>SO<sub>4</sub><small>(aq)</small> → CO<sub>2</sub><small>(g</small>) + H<sub>2</sub>O<small>(l)</small> + NaHSO<sub>4</sub><small>(aq).</small><ref name=":2" />

Reaction 4. Absorption of CO<sub>2</sub> and residual water

CO<sub>2</sub><small>(g)</small> + 2 NaOH<small>(s)  →</small> Na<sub>2</sub>CO<sub>3</sub><small>(s)</small> + H<sub>2</sub>O<small>(l)</small><small>.</small><ref name=":2" />