Group Members:
Bo Pang 庞博, AJ Cook


Barking Dog


Chemistry Background Information

3 NO + CS2 -> 3/2 N2 + CO + SO2 + 1/8 S8
4 NO + CS2 -> 2 N2 + CO2 + SO2 + 1/8 S8

When the NO gas and carbon disulfide mixed together and ignited, combustion wave travels down the tube and a barking sound was heard. It also produced many gasses such as carbon dioxide, carbon monoxide, nitrogen gas and sulfur dioxide. When it is ignited, it produced a blue light. The time of combustion and sound depended on the proportion of two gases. This demonstration showed a complex combustion reaction and how to know if a chemical reaction is happening.

In the first trial, excessive carbon disulfide caused there to be no sound and a slow combustion process. It showed us the color of the flame.

In the second trial, the right proportion of gases produced the barking sound of the reaction.

The bright blue emission accompanying the reaction corresponds to a spectroscopic continuum from 490-310 nm. The emission has been ascribed to a triplet-singlet transition in SO2.[3] Generation of triplet SO2 may follow this reaction path.
SO + N2O -> SO2 + N2
The formation of N2O probably involves the abstraction of O by CS2 or by CS from a collision dimer (N2O2). A much less intense emission of COS can be observed in the continuum of 550-700 nm. Several even weaker emissions can be observed for SO and S2. (chemistry demonstration book 1)

Chemical Reaction Indicators

There are four main indicators for a chemical rxn according to Hubbert 12
  1. Formation of heat or light
  2. Bubbles
  3. Formation of a precipitate
  4. Change in color
These indicators are specific to chemical reactions and can be seen independently to know that it was not only a physical reaction. Sometimes a physical reaction can occurrr which is different than chaning the chemical make up of a substance.

The pH of a solution, or the concentration of H+ ions, can be measured as well to see if a chemical reaction has occurred over time.

In our reaction we also heard a sound and saw the production of a gas as well, these helped us to know that a chemical reaction was taking place.

We saw the formation of heat and light that was occuring from excited electrons jumping down to their group state producing energy in the form of heat and light. We also saw a color change during the combustion of the gasses and during the production of the NO gas. The solution was originally clear nitric acid but then when it was added to the copper you saw it as a blue solution (as seen in the video) indicating that the copper was reduced to copper (II). When we added the copper to the nitric acid we also saw the production of a gas as seen by the orange color and bubbles that were developed in the solution. When the reaction was complete there was the foggy precipitate that formed on the inner side of the graduated cylinder.

Danger! Danger

This reaction is very dangerous and should you should not try it at home! NO gas is made by adding highly concentrated nitric acid to copper turnings and collected under the water. Both NO gas and carbon disulfide are extremely dangerous. NO will easily form nitrogen dioxide when exposed to the air. Nitrogen dioxide is toxic by inhalation, but this could be avoided as the material is pungent and easily detected by our sense of smell. One potential source of exposure is exposure to nitric acid, which is often contaminated with NO2. Symptoms of poisoning tend to appear several hours after one has inhaled a low but potentially fatal dose. Also, low concentrations will anesthetize the nose, thus creating a potential for overexposure. (from wikipedia).

Carbon disulfide is flammable and toxic too. At very high levels, carbon disulfide may be life-threatening because it affects the nervous system. Significant safety data come from the viscose rayon industry, where both carbon disulfide as well as small amounts of H2S may be present. (From wikipedia)
toxic.jpg

Additional Resources:
http://en.wikipedia.org/wiki/Carbon_disulfide
http://en.wikipedia.org/wiki/Nitrogen_dioxide
http://wiki.answers.com/Q/Indicators_in_chemical_reactions
References/Useful Links:
http://chemistry.about.com/od/chemistrydemonstrations/a/barkingdog.htm