Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: lablackey on December 09, 2008, 10:09:40 AM
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I am arguing with someone in my company who is supposedly a chemical engineer regarding the substitution of sodium carbonate for sodium hydroxide in one of our manufacturing processes.
Claims that we can calculate how much sodium carbonate is needed to replace the sodium hydroxide based on the fact that they both "contain" sodium oxide.
But even though
Na2O + H2O :rarrow: 2NaOH
In my mind the more pertinent equation what happens to sodium carbonate in water
Na2CO3 + 2H2O :rarrow: 2NaOH
I don't believe sodium carbonate can be said to "contain" sodium oxide. Am I correct? ???
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I don't believe sodium carbonate can be said to "contain" sodium oxide. Am I correct?
Yes and no. In some cases NaOH can be replaced by Na2CO3, and in many cases amount of Na2CO3 can be expressed in terms of Na2O it contains (same can be said about NaOH). So without further details it is hard to tell whether the other person is right, but using information supplied up to now, it is impossible to state that s/he is wrong either.
Have you seen fertilizers, as sold in gardener shops? Their composition is often written as 20% P2O5, 10% K2O and so on. It doesn't mean they specifically contain these oxides, it is just a way of stating composition. That's the same as Na2CO3/Na2O.
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Okay I see your point. But if we're talking, say, about the power of the compounds to neutralize an acid solution calculating the relative amounts of sodium hydroxide generated makes more sense to me than the sodium oxide.
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makes more sense, but if you write reaction equations you will see, that the result is the same - and to compare "neutralizing strength" of the NaOH and Na2CO3 you may convert both to Na2O.
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Thanks for answering. If I'm not bothering you too much I'd like to run one more part by you. :-\
I worked this next part out yesterday, and it turns out this is how the guy I'm sorta arguing with figures things as well:
Na2O + H2O :rarrow: 2NaOH
&
Na2CO3 combusts to form
CO2 + Na2O
Doing some molar conversions and looking up some data on a chemical supplier's website, it does seem that around 58% of Na2CO3 can be expressed as Na2O
Likewise, around 77% of NaOH is Na2O
So if my recipe calls for 1.26% NaOH based on dry starch (let's say 1000#), converting to sodium oxide = 12.6#/0.77 = 16.4#
To replace it with sodium carbonate 12.6#/0.58 = 21.7#
Which means to replace a pound of NaOH I would need 1.3# Na2CO3.
It seems like a valid calculation, but I'd like a second opinion. Thanks.
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Na2CO3 combusts to form
CO2 + Na2O
Not combustion, but thermal decomposition.
Which means to replace a pound of NaOH I would need 1.3# Na2CO3.
I have not traced your numbers but this final mass ratio - 1:1.3 - seems correct.
Obviously you can't always replace NaOH with Na2CO3, but that's another story. Sometimes you can.
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Okay, Thanks. :) The equations make sense, but since what I'm seeing experimentally is it takes 3-4 times as much sodium carbonate to achieve the same titer as sodium hydroxide I'm going to keep pondering this.
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Sodium carbonate tends to absorb huge amounts of crystallization water, up to Na2CO3.10H2O.
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Sodium carbonate tends to absorb huge amounts of crystallization water, up to Na2CO3.10H2O.
Yet it also gives up its water much easier than NaOH, which will simply fuse upon heating.
Lablackey, as Borek implies, your sodium carbonate is likely quite loaded with water and that is probably why you're having less success.
As for the original question, it would seem that your Chem. E is thinking on the absolute basis that one mole of sodium carbonate has one mole of sodium oxide in it which does the effective neutralization (the CO2. is obviously lost as gas). By "in it" I mean all things considered.