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Topic: lithium + h20??? why does this form hydrogen gas???  (Read 8820 times)

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Offline kevinnn

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lithium + h20??? why does this form hydrogen gas???
« on: April 12, 2011, 11:53:53 PM »
i still dont know the more in depth chemestry of why adding lithium to water ( or any of the first row elements ) creates hydrogen gas, any help would be great thanks :)

Offline opti384

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Re: lithium + h20??? why does this form hydrogen gas???
« Reply #1 on: April 13, 2011, 12:14:00 AM »
Why don't you write the reaction equation first and see?

Offline kevinnn

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Re: lithium + h20??? why does this form hydrogen gas???
« Reply #2 on: April 13, 2011, 12:18:13 AM »
yah i know the equation its 2Li + 2 h2O-----> 2LiOH + H2   

i still dont really understand though what is going on to a molecular level :,(

Offline opti384

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Re: lithium + h20??? why does this form hydrogen gas???
« Reply #3 on: April 13, 2011, 01:03:00 AM »
First of all, oxidation and reduction take place.

Offline kevinnn

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Re: lithium + h20??? why does this form hydrogen gas???
« Reply #4 on: April 13, 2011, 01:17:57 AM »
we have not actually not covered oxidation and reduction yet in class.  but i do have a understanding of it, but could you help explane it to me in the contex of this problem???

Offline opti384

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Re: lithium + h20??? why does this form hydrogen gas???
« Reply #5 on: April 13, 2011, 01:25:32 AM »
Oxidation is, in general, the process in which an atom or a compound loses electrons. Reduction is the process in which they gain electrons. In an equation, we use the oxidation number to easily figure out which is oxidized and reduced.

Offline DevaDevil

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Re: lithium + h20??? why does this form hydrogen gas???
« Reply #6 on: April 13, 2011, 11:26:17 AM »
in short: lithium atoms donate an electron to protons (H+) in the water to form the hydrogen gas. The protons are present due to the water equilibrium:
H2O <--> H+ + OH-

The thus formed lithium cation will stay in solution, and upon evaporating the water will recombine with the excess OH- (because the protons were used to make water) to form LiOH

Offline kevinnn

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Re: lithium + h20??? why does this form hydrogen gas???
« Reply #7 on: April 13, 2011, 09:49:10 PM »
in short: lithium atoms donate an electron to protons (H+) in the water to form the hydrogen gas. The protons are present due to the water equilibrium:
H2O <--> H+ + OH-

The thus formed lithium cation will stay in solution, and upon evaporating the water will recombine with the excess OH- (because the protons were used to make water) to form LiOH

ok thank you for the help now let me see if i am comprhending this correctly.  you are saying that when i drop lithium in water the lithium will disolve in the water and when it dissolves it will donate one of its electrons to a proton.  now is it donating an electron to hydrogen to give it a full outer shell???  if this is the case does hydrogen escape as H instead of H2??  and when the electrons are donated does this rip the water molecule apart?? if so how? does it make it more stable??  and when the water molecule breaks apart to form hydrogen and a hydroxide does the now aqueous lithium that started the reaction bonds with OH- to form the now not reactive anymore in the solution sodium hydroxide??  i know i am probably missing stuff but is there anything incorrect here too??? thanks :)  

Offline KyleH

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Re: lithium + h20??? why does this form hydrogen gas???
« Reply #8 on: April 13, 2011, 10:05:05 PM »
You're close Kevin.  Hydrogen pretty much exist in nature only as H2.  since you're adding Lithium's electron to a PROTON (H+), it will only become H, which is still missing an electron from it's outer valence, which is why it goes and covalently bonds with another H, to make H2.  notice the break down of H2O ---> H+   +   OH-.  THe oxygen has such a high electronegativity that when one of the H's leaves, the Oxygen will keep that electron, making OH-, and the leftover hydrogen atom H+.  The OH- is what attracts Li+ to it to make LiOH.  

This is a pretty simple explanation because of you not knowing about oxidation and reduction yet.  Also if I have made any errors, anybody can feel free to let me know

Also to clarify some of your other questions - hydrogen has a higher ability to gain electrons (reduce) then lithium, so yes the H2O does get ripped apart.  The products (H2 and LiOH) of the reaction would be more stable since that is why spontaneous chemical reactions occur.  

Offline kevinnn

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Re: lithium + h20??? why does this form hydrogen gas???
« Reply #9 on: April 13, 2011, 10:19:52 PM »
     Thank you very much, this does help. 
     Yeah my class really needs to get to oxidation and reduction cuz it is definitely a very important thing, and i only have a good understanding of it in context of marine enviorments.   

Offline vmelkon

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Re: lithium + h20??? why does this form hydrogen gas???
« Reply #10 on: April 18, 2011, 08:39:48 AM »
I don't think there is a lot of H+ around. Most of it is H2O and the reaction would proceed in steps

Li + H2O => LiHO
Li + LiHO => Li2O
Li2O + H2O => LiOH

Offline rabolisk

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Re: lithium + h20??? why does this form hydrogen gas???
« Reply #11 on: April 18, 2011, 08:46:38 AM »
I don't think there is a lot of H+ around. Most of it is H2O and the reaction would proceed in steps

Li + H2O => LiHO
Li + LiHO => Li2O
Li2O + H2O => LiOH

None of that is balanced, and it makes no sense at all. It doesn't explain why hydrogen is evolved.

Offline DrCMS

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Re: lithium + h20??? why does this form hydrogen gas???
« Reply #12 on: April 18, 2011, 08:49:22 AM »
I don't think there is a lot of H+ around. Most of it is H2O and the reaction would proceed in steps

Li + H2O => LiHO
Li + LiHO => Li2O
Li2O + H2O => LiOH

Stop making stuff up and try balancing these quations.

Lithium reacts with water to give lithium hydroxide and hydrogen gas.  




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