[shafer5]

Ok, I'm taking a chemistry class and my first lab was last weds.  Either the teacher was being very speedy or it was just me being slow trying to do everything right...but my partner and I didn't get through the lab.  So if anyone could help with the following questions it would be greatly appreciated!

1. What role does the sodium bicarbonate play in the generation of carbon dioxide? (we put sodium bicarbonate in the bottom corner of a plastic bag and added hydrochloric acid.)

2. What role does potassium iodide play in the generation of oxygen? How does this differ from the role of sodium bicarbonate in the production of carbon dioxide? (We put potassium iodide in the bottom corner of a plastic bag then added hydrogen peroxide.)

3. Does exhaled air contain more CO2 than normal air?  What evidence do you have for your answer?

4. Based on what you observed about the interaction of carbon dioxide with the glowing splint, explain how CO2 fire extinguishers work.

5.Based on what you observed about the interaction of oxygen with the glowing splint, explain why liquid oxygen is an extremely hazardous material.

6. Propose a way to estimate the volume of oxygen that was generated in the plastic bag.


(Not sure if anyone can help me considering we did the experiments in class)

[Alpha-Omega]

So for questions #4 and #5

What did you see?  You have not commented on what you observed....

[shafer5]

4. Based on what you observed about the interaction of carbon dioxide with the glowing splint, explain how CO2 fire extinguishers work.

The glowing splint went out when we put the glowing splint into the bag.

5.Based on what you observed about the interaction of oxygen with the glowing splint, explain why liquid oxygen is an extremely hazardous material.

When we put the glowing splint into the bag the glow turned into a flame.

[Arkcon]

To answer 1 through, well, all of them, we'd need to know what you did. I can guess, but it would be easier to talk you through the questions if we're all on the same page.

[shafer5]

To answer 1 through, well, all of them, we'd need to know what you did. I can guess, but it would be easier to talk you through the questions if we're all on the same page.

I guess that would help huh? lol I'll edit my post real quick here

[Alpha-Omega]

1) sodium bicarb is often used to neutralize acids (spills) in the process CO2 is generated....this is a decomposition reaction:

Reaction of sodium bicarbonate and an acid:

NaHCO₃ + HCl → NaCl + H₂CO₃

This then decomposes into carbon dioxide and water:

H₂CO₃ → H₂O+ CO₂ (gas)

NaHCO₃ + CH₃COOH → CH₃COONa + H₂O + CO₂ (gas)

2)  The decomposition of hydrogen peroxide into water and oxygen gas.  Reactions like these that are both oxidations and reductions are known as disproportionation reactions.  The KI acts as a catalyst in the decomposition of the H2O2....the KI does not participate.  A catalyst is a substance that increases the rate of a chemical reaction without being consumed in the reaction.  Here the iodide ion is conserved.

The charges change because this is a redox reactionn...but this is disproportionation.

Basically:  K is a spectator ion
I^- is oxidized... as peroxide is reduced
peroxide is reduced to water
2I^- is oxidized to I₂


H₂O₂(aq) + I^-(aq) -> OI^-(aq) + H₂O(l)

H₂O₂(aq) + OI^-(aq) -> H₂O(l) + O₂(g) + I^-(aq)

In 1) the sodium bicarbonate actually participates in the reaction.  The sodium bicarbonate is not a spectator species or a catalyst. It is consumed in the decomposition reaction.

3)  Read This:  http://en.wikipedia.org/wiki/CO2     and      http://www.dhfs.state.wi.us/eh/ChemFS/fs/CarbonDioxide.htm

4) Carbon dioxide (CO2) extinguishers contain a mixture of liquid and gaseous carbon dioxide (a nonflammable gas). CO2 is normally a gas at room temperature and pressure. It has to be stored under high pressure to make it a liquid. When you release the pressure, the gas expands enormously and cools to make a huge white jet. CO2 attacks the fire triangle in two ways: it smothers the oxygen and, because it's so cold, it also removes heat. You will ahve to relate this to what you observed.

5) From Wikipedia:  gaseous and liquid oxygen will act as a fuel; and therefore the design and manufacture of oxygen systems requires special training to ensure that ignition sources are minimized. The fire that killed the Apollo 1 crew on a test launch pad spread so rapidly because the capsule was pressurized with pure oxygen but at slightly more than atmospheric pressure, instead of the ⅓ normal pressure that would be used in a mission.

Liquid oxygen spills, if allowed to soaked into organic matter, such as wood, petrochemicals, and asphalt can cause these materials to detonate unpredictably on subsequent mechanical impact.  On contact with the human body, it can also cause cryogenic burns to the skin and the eyes.

see: http://en.wikipedia.org/wiki/Oxygen  and relate this to what you observed.


6) I was not ther and you did not describe this so...at a loss on this one.

[shafer5]

Thanks so much for your help

[shafer5]

For #6 here are the instructions, I didn't actually get to do this.

-Breathe in and then exhale into a 1 pint heavy duty zipper bag, repeating this 2 or 3 times; then seal the bag when it is inflated with your breath.

[Alpha-Omega]

1) Determine volume of bag.

Then, because you breateh air and it is a mixture...

2) Apply the N2/O2 ratio

See this link for the composition of air:  http://en.wikipedia.org/wiki/Air

[shafer5]

Thanks for all your help Alpha-Omega...I'm sure I'll be back for more, this stuff is extremely interesting

[Alpha-Omega]

OKee Dokee Duckie...No problem!!!