Chemistry:Dry ice color show

From HandWiki

File:Dry ice experiment.webm

The dry ice color show is a chemical demonstration for the formation of carbonic acid (H2CO3) by the dissolution of dry ice, the solid form of carbon dioxide (CO2) into water.[1] Carbonic acid is a weak acid and solutions are not hazardous. It is present in numerous consumer products including tonic water, soda, and beer. However, carbonic acid solutions are sufficiently acidic at pH of 4.18 at 10 mM concentration to be registered by many pH indicators. The dry ice color demonstration is usually performed in classrooms to show the properties of pH, sublimation, and indicators, particularly due to its ease of set up and low hazards.[2] The primary hazard is dry ice's ability to cause frostbite upon skin contact.

Description

This experiment provides effective explanation of the acids, bases, indicators reaction and also the properties of carbon dioxide.[3] A large amount of the universal indicator, is first added to water for detecting the change of solution's pH. Then, a few drop of ammonia or sodium hydroxide is mixed into the solution, which changes the color of the solution to a deep green color. Subsequently, the addition of dry ice is required to alter the pH of the solution from basic to acidic condition.[4] Carbonic acid formed when dry ice is added to the liquid sample and lowers the pH. This alters the solution from weakly basic to acidic identified by the color change from green to yellow.[5] Thus, the solution's color gradually turns from deep green into orange color as more hydrogen ions aggregate in the solution.[6] Simultaneously, the cloud of carbon dioxide is generated from the sublimation process, direct change of solid to gas phase, due to the condensation of water vapor in the air.[7]

Chemical explanation

Ammonia is a weak alkali that reacts reversibly with water and alters the pH of the solution into base condition.

NH3(g) + H2O(l) ⇌ NH4+(aq) + OH−(aq)[8][9]

On the other hand, if sodium hydroxide is added to adjust the pH of the solution to alkali, the color change develops faster than the ammonia as it is a highly reactive compound.

2NaOH(aq) + CO2(g) ⇌ Na2CO3(aq) + H2O(l)[10]

When dry ice is added to water, it sublimes to carbon dioxide gas rapidly because the solution's temperature is warmer than the dry ice (-78.5 C° or -109.3 F°). This gas can be observed as bubbles or clouds above the solution.[7] Since the temperature of the gas is so cold, the water vapor containing in the air above the water condenses into small water droplets or clouds suspending in the carbon dioxide gas.[2]

CO2(s) ⇌ CO2(g)

However, some of them react reversibly with water molecules to form acidic solution symbolized by the production of hydrogen ion.[6]

CO2(aq) + H2O(l) ⇌ HCO3−(aq) + H+(aq)[9]

When the acidic solution is mixed together with the alkali present in the solution, the solution, overall, becomes neutral.

HCO3−(aq) + H+(aq) + NH4+(aq) + OH−(aq) ⇌ NH4+(aq) + HCO3−(aq) + H2O(l) (addition of ammonia)

HCO3−(aq) + H+(aq) + Na+(aq) + OH−(aq) ⇌ Na+(aq) + HCO3−(aq) + H2O(l) (addition of sodium hydroxide)[8]

The color of the solution changes due to the universal indicator, a pH detector. Once the alkali-to-acid universal indicator is incorporated into the solution, the color of the solution changes corresponding to the acidic color of the universal indicator. The color of ammonia and water only is green. However, once the dry ice is added, the solution slowly turns orange as more hydrogen ions are continuously produced.[6]

Precautions

Dry ice sublimates at –78.5 °C (109.3°F) and is a cryogenic hazard. Proper PPE including appropriate gloves are required when handling, and bare skin contact should be avoided.[11] Dry ice will naturally sublimate away in ambient air, but should always be kept in a well-ventilated area to prevent hazardous buildup of carbon dioxide gas or displace oxygen. Carbon dioxide over-exposure can result in shortness of breath, headache, hyperventilation, anxiety and can trigger panic attacks in vulnerable individuals.[12]

References

  1. ↑ Flinn Scientific, Inc. (2016). "Dry Ice Color Show". Scientific: 5. https://www.flinnsci.ca/globalassets/flinn-scientific/all-free-pdfs/dc95016.pdf. 
  2. ↑ 2.0 2.1 "Dry Ice!". 2004. http://www.abc.net.au/science/surfingscientist/pdf/lesson_plan08.pdf. 
  3. ↑ "Indicators and dry ice demonstration". rsc.org. http://www.rsc.org/learn-chemistry/resource/res00000703/indicators-and-dry-ice-demonstration. 
  4. ↑ "Dry Ice Color Show". https://www.flinnsci.com/dry-ice-color-show/dc10417/. 
  5. ↑ "Dry Ice Color Change". 24 November 2015. http://www.zlifeeducation.com/category/dry-ice-color-change/. 
  6. ↑ 6.0 6.1 6.2 "Acidic Properties of CO2 in Aqueous Solutions". 2012. https://ocw.mit.edu/high-school/chemistry/demonstrations/videos/colorful-indicators/Indicators.pdf. 
  7. ↑ 7.0 7.1 "Carbon Dioxide Properties". 2012. http://www.vanderbilt.edu/cso/CO2_Properties.pdf. 
  8. ↑ 8.0 8.1 "Indicators and dry ice demonstration- Learn Chemistry" (in en). http://www.rsc.org/learn-chemistry/resource/res00000703/indicators-and-dry-ice-demonstration. 
  9. ↑ 9.0 9.1 Shakhashiri, Bassam Z. (1985). Chemical Demonstrations Volume 2. Wisconsin, USA. pp. 118–119. ISBN 0-299-10130-4. 
  10. ↑ "Demo 24: Acidity Change of Dry Ice in Water" (in en). http://www-chem.ucsd.edu/undergraduate/teaching-labs/demos/demo24.html. 
  11. ↑ "Dry Ice Color Show". Flinn Scientific. 2016. https://www.flinnsci.com/globalassets/flinn-scientific/all-free-pdfs/dc10417.pdf. 
  12. ↑ Shilpa, Gowda. "New Insight into Panic Attacks: Carbon Dioxide is the Culprit". Journal of Young Investigators. https://www.jyi.org/2007-november/2007/11/10/new-insight-into-panic-attacks-carbon-dioxide-is-the-culprit. 



Retrieved from "https://handwiki.org/wiki/index.php?title=Chemistry:Dry_ice_color_show&oldid=1061631"