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Topic: Stoichiometry Problem  (Read 4120 times)

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Offline pearljamvs5

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Stoichiometry Problem
« on: March 24, 2007, 10:01:23 AM »
In my Chemistry II class, my teacher did an experiment involving dropping solid Sodium metal into a beaker filled with distilled water, which caused an explosion that shattered the beaker. After the experiment, he gave us this problem to answer, which counts as four test grades:

The density of Sodium metal is 0.97g/cm³. If Mr. Oliver used a rectangular prism of Sodium metal 2.50 cm x 1.00 cm x 0.50 cm, how many liters of Hydrogen and Oxygen gas at 500°C and 1.00 atATMould be produced when placed in ¾ of a liter of water? Would the Hydrogen and Oxygen be in a perfect stoichiometric mixture?

He also gave us these balanced chemical equations which he said would help us solve this problem:

1. 2Na + 2H2O   2NaOH + H2

2. 4Na + O2   2Na2O

   ?H   
3. 2Na2O   Na2O2 + 2Na
   400°C

4. Na2O2 +2H2O2   H2O2 + 2NaOH

   ?H
5. H2O2   2H2O + O2

6. 2H2 + O2   2H2O

Side reaction = Na2O + H2O   2NaOH

This is due on Monday, and if anybody could please help me with this, I would REALLY appreciate it!

Offline Sam (NG)

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Re: Stoichiometry Problem
« Reply #1 on: March 24, 2007, 03:43:37 PM »
This problem confuses me slightly for several reasons:

1) i've never seen sodium explode on contact with water.
2)How do you place sodium in a beaker of water at 500°C?
3)I don't know about at 500°C, but at rtp, i am fairly sure that only hydrogen gas is produced, not Oxygen gas.

Offline pearljamvs5

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Re: Stoichiometry Problem
« Reply #2 on: March 24, 2007, 04:09:53 PM »
My teacher had pieces of solid sodium and when he placed the bigger pieces in the beaker, they actually produced a yellow fire and exploded

Online Borek

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Re: Stoichiometry Problem
« Reply #3 on: March 24, 2007, 06:11:57 PM »
i've never seen sodium explode on contact with water.

http://www.chemicalforums.com/index.php?topic=12381.0

See video linked to from the first post.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

Offline Sam (NG)

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Re: Stoichiometry Problem
« Reply #4 on: March 24, 2007, 06:18:39 PM »
Nice, my teacher (way back when) was obviously far too safety concious to use a piece big enough to cause an explosion.  I'm interested now about the products of the reaction between Sodium and Water.  Is it just hydrogen gas, or hydrogen and oxygen gas as stated in the question?

To answer the question, can you use pV=nRT or have you got to consider the gas as not ideal?
If you can, then remember to convert litres to metres cubed and use pascals for pressure with R=8.314.

The balanced equation for the reaction with water is:

2Na + 2H2O ---> 2NaOH + H2

So in order to calculate the number of moles of hydrogen gas produced you have to calculate the number of moles of sodium used in the first place from the volume and density, then divide by 2 because of the stoichiometric equation to give you the number of moles of hydrogen that should be produced.

from here rearrange the ideal gas equation to give

V=nRT/p

From this you can get the volume of the hydrogen produced from the reaction.

Remember to use Temperature in degrees kelvin.

This is just my guess, i'm not sure why the rest of the side reactions are included, but they are obviously there for a reason.
« Last Edit: March 24, 2007, 06:42:56 PM by Sam (UoN) »

Offline pearljamvs5

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Re: Stoichiometry Problem
« Reply #5 on: March 24, 2007, 07:06:02 PM »
Yeah, one of the kids in my class was using pV=nRT so I guess it is considered ideal. I guess my teacher isn't very safetly cautious since he is always doing crazy things like making things explode and lighting the gas jet with a match.

My teacher is really smart, however, its really hard to understand him when he tries to explain things because of this. Anyway, this was very helpful so thank you so much!

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