H2S
Harmless
Posts: 1
Registered: 4-1-2009
Member Is Offline
Mood: No Mood
|
|
Carbon dioxide and Manganese (II) hydroxide?
Hello- first time posting here. Hoping you can help.
I recall reading about a "high school level" biology lab that was measuring respiration. In this experiment, a small amount of potassium hydroxide
(solid) was placed in the bottom of a test tube to absorb atmospheric carbon dioxide. However, the lab did not report the equation for this reaction.
From what I can gather online:
KOH(s) + CO2(g) → KHCO3(s)
I don't know the accuracy of this equation, though it is balanced.
Here's the question:
Can a similar reaction occur with dissolved CO2 (not carbonic acid) and an insoluble metal hydroxide such as Mn(OH)2 in water?
Also, can the reaction occur with other manganese species, such as manganese (IV)?
Thank you for your help.
|
|
|
kclo4
National Hazard
Posts: 916
Registered: 11-12-2004
Location:
Member Is Offline
Mood: No Mood
|
|
It probably can, although I am not totally sure. A way you could do this is dissolve the Manganese compound in an acid, and then preform a double
displacement reaction with Sodium Carbonate, or Sodium Bicarbonate. Manganese bicarbonate may not be stable though, so the evolution of carbon dioxide
might occur. Keeping the solution very cool may allow the bicarbonate to exist.
I have made Copper Carbonate using Copper sulfate and Sodium Bicarbonate. A lot of Carbon Dioxide was released as the greenish blue carbonate
precipitated out.
form what you have been able to gather online of CO2 and KOH reacting is correct however potassium carbonate will form first, and then when enough CO2
is added, it will start producing the potassium bicarbonate.
2KOH + CO2 = K2CO3 + H2O
K2CO3 + H2O + 2 CO2 = 2 KHCO3
Also KHCO3 + KOH = K2CO3 + H2O (so, virtually all of the KOH has to be reacted in solution before KHCO3 can start to form, other wise it will just
react to form K2CO3)
|
|
|
not_important
International Hazard
Posts: 3873
Registered: 21-7-2006
Member Is Offline
Mood: No Mood
|
|
Mn(OH)2 is slightly soluble in water, if moist and with excess CO2 it will slowly react to give the carbonate. It also reacts with oxygen in air to
given some Mn(III) hydrated oxide - in effect 2Mn(OH)2 + O2 => 2H2O + 2MnO(OH). The higher oxidation states of manganese don't form carbonates,
they act more like acids than bases.
You can't really say "dissolved CO2 (not carbonic acid)" because you can't prevent the interaction of CO2 and water. I'm not sure that extensively
dried KOH and CO2 would react, many compounds do not react or only reaxct slowly when completely dry.
|
|
|
kclo4
National Hazard
Posts: 916
Registered: 11-12-2004
Location:
Member Is Offline
Mood: No Mood
|
|
If extensively dried KOH did react with CO2 at any rate, wouldn't it produce H2O and allow for even more of it react at a faster rate?
Or maybe it would form carbonate shell on it preventing further reaction.
|
|
|
not_important
International Hazard
Posts: 3873
Registered: 21-7-2006
Member Is Offline
Mood: No Mood
|
|
yes, it would accellerate the reaction; an auto-catalytic effect if you will. The carbonate would also dissolve in the water, so you'd get a thin
saturated solution on the exposed surfaces. But it takes even less water than that, not even a monolayer.
|
|
|
kclo4
National Hazard
Posts: 916
Registered: 11-12-2004
Location:
Member Is Offline
Mood: No Mood
|
|
Could you explain what you mean by "But it takes even less than that, not even a monolayer." I find that confusing for some reason..
Are you saying the Na2CO3 will form a layer less then one atom thick to prevent CO2 from continuing to react with the NaOH?
|
|
|
not_important
International Hazard
Posts: 3873
Registered: 21-7-2006
Member Is Offline
Mood: No Mood
|
|
Ah, no, you don't even need a full layer of absorbed water to greatly accelerate reactions.
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
