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Cooling bath
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<h2 id="mixed-solvent-cooling-baths">Mixed-solvent cooling baths</h2> <p>Mixing solvents creates cooling baths with variable freezing points. Temperatures between approximately −78 °C and −17 °C can be maintained by placing coolant into a mixture of <a href="/facts/Ethylene_glycol/stFz6CVe">ethylene glycol</a> and <a href="/facts/Ethanol/3lCLfBSP">ethanol</a>,<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a> while mixtures of <a href="/facts/Methanol/EIfpoNCg">methanol</a> and <a href="/facts/Water/0lkXnJPK">water</a> span the −128 °C to 0 °C temperature range.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a><a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> Dry ice <a href="/facts/Sublimation_(phase_transition)/KDoKokMn">sublimes</a> at −78 °C, while <a href="/facts/Liquid_nitrogen/IGWI1h00">liquid nitrogen</a> is used for colder baths. </p><p>As water or ethylene glycol freeze out of the mixture, the concentration of ethanol/methanol increases. This leads to a new, lower freezing point. With dry ice, these baths will never freeze solid, as pure methanol and ethanol both freeze below −78 °C (−98 °C and −114 °C respectively). </p><p>Relative to traditional cooling baths, solvent mixtures are adaptable for a wide temperature range. In addition, the solvents necessary are cheaper and less toxic than those used in traditional baths.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> </p> <h2 id="traditional-cooling-baths">Traditional cooling baths</h2> Traditional cooling bath mixtures<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a><table><tbody><tr><th>Cooling agent</th><th>Organic solvent or salt</th><th>Temp (°C)</th></tr><tr><td>Dry ice</td><td><i>p</i>-xylene</td><td>+13</td></tr><tr><td>Dry ice</td><td>Dioxane</td><td>+12</td></tr><tr><td>Dry ice</td><td>Cyclohexane</td><td>+6</td></tr><tr><td>Dry ice</td><td>Benzene</td><td>+5</td></tr><tr><td>Dry ice</td><td>Formamide</td><td>+2</td></tr><tr><td>Ice</td><td>Salts (see: left)</td><td>0 to −40</td></tr><tr><td>Liquid N2</td><td>Cycloheptane</td><td>−12</td></tr><tr><td>Dry ice</td><td>Benzyl alcohol</td><td>−15</td></tr><tr><td>Dry ice</td><td>Tetrachloroethylene</td><td>−22</td></tr><tr><td>Dry ice</td><td>Carbon tetrachloride</td><td>−23</td></tr><tr><td>Dry ice</td><td>1,3-Dichlorobenzene</td><td>−25</td></tr><tr><td>Dry ice</td><td><i>o</i>-Xylene</td><td>−29</td></tr><tr><td>Dry ice</td><td><i>m</i>-Toluidine</td><td>−32</td></tr><tr><td>Dry ice</td><td>Acetonitrile</td><td>−41</td></tr><tr><td>Dry ice</td><td>Pyridine</td><td>−42</td></tr><tr><td>Dry ice</td><td><i>m</i>-Xylene</td><td>−47</td></tr><tr><td>Dry ice</td><td><i>n</i>-Octane</td><td>−56</td></tr><tr><td>Dry ice</td><td>Isopropyl ether</td><td>−60</td></tr><tr><td>Dry ice</td><td>Acetone</td><td>−78</td></tr><tr><td>Liquid N2</td><td>Ethyl acetate</td><td>−84</td></tr><tr><td>Liquid N2</td><td><i>n</i>-Butanol</td><td>−89</td></tr><tr><td>Liquid N2</td><td>Hexane</td><td>−94</td></tr><tr><td>Liquid N2</td><td>Acetone</td><td>−94</td></tr><tr><td>Liquid N2</td><td>Toluene</td><td>−95</td></tr><tr><td>Liquid N2</td><td>Methanol</td><td>−98</td></tr><tr><td>Liquid N2</td><td>Cyclohexene</td><td>−104</td></tr><tr><td>Liquid N2</td><td>Ethanol</td><td>−116</td></tr><tr><td>Liquid N2</td><td><i>n</i>-Pentane</td><td>−131</td></tr><tr><td>Liquid N2</td><td>Isopentane</td><td>−160</td></tr><tr><td>Liquid N2</td><td>(none)</td><td>−196</td></tr></tbody></table> <h3>Water and ice baths</h3> <p>A bath of ice and water will maintain a temperature 0 °C, since the <a href="/facts/Melting_point/MY0w0h0k">melting point</a> of water is 0 °C. However, adding a salt such as <a href="/facts/Sodium_chloride/MWcXl3Mb">sodium chloride</a> will lower the temperature through the property of <a href="/facts/Freezing-point_depression/B5fSARUv">freezing-point depression</a>. Although the exact temperature can be hard to control, the weight ratio of salt to ice influences the temperature: </p> <ul><li>−10 °C can be achieved with a 1:2.5 mass ratio of calcium chloride hemihydrate to ice.</li> <li>−20 °C can be achieved with a 1:3 mass ratio of sodium chloride to ice.</li></ul> <h3>Dry ice baths at −78 °C</h3> <p>Since dry ice will <a href="/facts/Sublimation_(phase_transition)/KDoKokMn">sublime</a> at −78 °C, a mixture such as acetone/dry ice will maintain −78 °C. Also, the solution will not freeze because acetone requires a temperature of about −93 °C to begin freezing. </p> <h3>Safety recommendations</h3> <p>The <a href="/facts/American_Chemical_Society/Alf3uhaF">American Chemical Society</a> notes that the ideal organic solvents to use in a cooling bath have the following characteristics: </p> <ol><li>Nontoxic vapors.</li> <li>Low viscosity.</li> <li>Nonflammability.</li> <li>Low volatility.</li> <li>Suitable freezing point.</li></ol> <p>In some cases, a simple substitution can give nearly identical results while lowering risks. For example, using dry ice in <a href="/facts/2-propanol/7KqgIkUd">2-propanol</a> rather than acetone yields a nearly identical temperature but avoids the volatility of acetone (see § Further reading below). </p> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/List_of_cooling_baths/hFzFmoHo">List of cooling baths</a></li> <li><a href="/facts/Pumpable_ice_technology/AGPkS6Tp">Pumpable ice technology</a></li></ul> <h2 id="further-reading">Further reading</h2> <ul><li>Jonathan M. Percy; Christopher J. Moody; Laurence M. Harwood (1998). <a href="https://archive.org/details/experimentalorga0002harw"><i>Experimental Organic Chemistry: standard and microscale</i></a>. <a href="/facts/Blackwell_Publishing/XUkBW8kE">Blackwell Publishing</a>. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 978-0-632-04819-9.</li> <li>Wilfred Louis Florio Armarego; Christina Li Lin Chai (2003). <i>Purification of Laboratory Chemicals</i> (5th ed.). <a href="/facts/Butterworth-Heinemann/c9nUxIVF">Butterworth-Heinemann</a>. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 978-0-7506-7571-0.</li> <li>Kenneth P. Fivizzani (2003). <i>Safety in Academic Chemistry Lab, by American Chemical Society, Volume 1: Accident Prevention for College and University Students</i> (7th ed.). <a href="/facts/American_Chemical_Society/Alf3uhaF">American Chemical Society</a>. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 9780841238633.</li></ul> <h2 id="external-links">External links</h2> <ul><li>Carter Research Group. <a href="http://oregonstate.edu/dept/chemistry/carter/cooling-bath-table">"Cooling Baths"</a>. <a href="/facts/Oregon_State_University/FR0MGWWg">Oregon State University</a>.</li> <li>A. J. Meixner; et al. <a href="http://www2.uni-siegen.de/~pci/versuche/english/v105-2.html">"10.5.2 Different Freezing Mixtures"</a>. <a href="/facts/University_of_Siegen/5hYGr6aR">University of Siegen</a>.</li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Lee, Do W.; Jensen, Craig M. (2000). "Dry-Ice Bath Based on Ethylene Glycol Mixtures". J. Chem. Educ. 77 (5): 629. Bibcode:2000JChEd..77..629J. doi:10.1021/ed077p629. <a href="http://jchemed.chem.wisc.edu/Journal/issues/2000/May/abs629.html" target="_blank">http://jchemed.chem.wisc.edu/Journal/issues/2000/May/abs629.html</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Lee, Do W.; Jensen, Craig M. (2000). "Dry-Ice Bath Based on Ethylene Glycol Mixtures". J. Chem. Educ. 77 (5): 629. Bibcode:2000JChEd..77..629J. doi:10.1021/ed077p629. <a href="http://jchemed.chem.wisc.edu/Journal/issues/2000/May/abs629.html" target="_blank">http://jchemed.chem.wisc.edu/Journal/issues/2000/May/abs629.html</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Methanol/Water mixtures make great cooling baths. Chemtips.wordpress.com. Retrieved on 2015-02-23. <a href="https://chemtips.wordpress.com/2015/02/09/methanolwater-mixtures-make-great-cooling-baths/" target="_blank">https://chemtips.wordpress.com/2015/02/09/methanolwater-mixtures-make-great-cooling-baths/</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>The ridiculously thorough guide to making a MeOH/Water bath. Chemtips.wordpress.com. Retrieved on 2015-02-23. <a href="https://chemtips.wordpress.com/2015/02/23/the-ridiculously-thorough-guide-to-making-a-meohwater-bath/" target="_blank">https://chemtips.wordpress.com/2015/02/23/the-ridiculously-thorough-guide-to-making-a-meohwater-bath/</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Lee, Do W.; Jensen, Craig M. (2000). "Dry-Ice Bath Based on Ethylene Glycol Mixtures". J. Chem. Educ. 77 (5): 629. Bibcode:2000JChEd..77..629J. doi:10.1021/ed077p629. <a href="http://jchemed.chem.wisc.edu/Journal/issues/2000/May/abs629.html" target="_blank">http://jchemed.chem.wisc.edu/Journal/issues/2000/May/abs629.html</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>Cooling baths – ChemWiki. Chemwiki.ucdavis.edu. Retrieved on 2013-06-17. <a href="http://chemwiki.ucdavis.edu/VV_Lab_Techniques/Cooling_baths" target="_blank">http://chemwiki.ucdavis.edu/VV_Lab_Techniques/Cooling_baths</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> </ol>