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melvados · Sep 27, 2009, 07:58 PM

Hi all, I'm new here but in need of help in chemical equations and theory. Have tried reading up some books but none have really given what I really wanted.

1. I am trying to balance the following equations but not sure if its correct, could anyone help me check as it seems weird for me?
- Zinc + sodium carbonate : Zn + Na2CO3 --> ZnCO3 + Na2?
- Copper + Sodium carbonate: Cu + Na2CO3 --> CuCO3 + Na2?

2. I am doing an experiment to see if metals, zinc and copper will react in alkaline solution which is the sodium carbonate solution.
I know that when such metals reacts in certain solutions, a layer of oxide (zinc /copper oxide) will be formed on the surface of the metal.
So if I put the metals in sodium carbonate solution, will there be a layer of oxide (zinc oxide or copper oxide) also formed on the surface of the metals?

If there really is an oxide formed, can I say that this oxide will actually give a weight gain (though the value will be very small) onto these metals if taken for readings?

Greatly appreciated for any answers/help given. Thanks in advance

Unknown008 · Sep 28, 2009, 07:10 AM

1. We denote 2 sodiums by putting the number in front of the formula:

$Zn + Na_2CO_3 \rightarrow ZnCO_3 + 2Na$
$Cu + Na_2CO_3 \rightarrow CuCO_3 + 2Na$

It's good. :)

2. No, there isn't any oxide formed. However, all metals (the majority of them) have a layer of oxide before an experiment is performed because the metal reacts with the oxygen in the air (very slowly).

If you weight all the system, you have no weight gain or loss.
Weight gain or loss may be observed when air is involved, because you are not weighing the air surrounding the reaction.

Say oxygen is absorbed. Then, there will be weight gain.
If however oxygen, or carbon dioxide is produced, the air will bubble out of the reacting solution and you'll observe a decrease in weight.

I hope that made sense. Don't hesitate to ask if you have any doubts, or don't understand something :)

Perito · Sep 28, 2009, 10:55 AM

Originally Posted by melvados

1. I am trying to balance the following equations but not sure if its correct, could anyone help me check as it seems weird for me?
- Zinc + sodium carbonate : Zn + Na2CO3 --> ZnCO3 + Na2?
- Copper + Sodium carbonate: Cu + Na2CO3 --> CuCO3 + Na2?

2. I am doing an experiment to see if metals, zinc and copper will react in alkaline solution which is the sodium carbonate solution.
I know that when such metals reacts in certain solutions, a layer of oxide (zinc /copper oxide) will be formed on the surface of the metal.
So if i put the metals in sodium carbonate solution, will there be a layer of oxide (zinc oxide or copper oxide) also formed on the surface of the metals?

If there really is an oxide formed, can i say that this oxide will actually give a weight gain (though the value will be very small) onto these metals if taken for readings?

1. Unknown008 balanced the equations for you, but there's no way that zinc or copper will release sodium metal. The reactions will not occur as written, above. This would be what I would expect (note the arrows).

$Zn + Na_2CO_3 \leftarrow ZnCO_3 + 2Na$
$Cu + Na_2CO_3 \leftarrow CuCO_3 + 2Na$

2. Zinc will replace copper.

The oxide will give a weight gain, though it would be very small.

Copper forms an oxide layer fairly slowly compared to some other metals, and the oxide layer is not very thick or heavy. If you really wanted to be sure that it didn't oxidize, you'd have to clean it off under an inert atmosphere (argon or nitrogen) and use it in there. For most work, I would use steel wool to clean the oxide from the copper, and then I would weigh it and use if directly.

Zinc is more reactive than copper but I'd probably do the same for zinc as for copper.

melvados · Sep 28, 2009, 08:18 PM

Thank you all for your prompt reply, unknown008 and Perito.

I read somewhere where it says that sodium carbonate will absorbs the oxygen in the air (not quite remember), is that true?

If not, then regarding to the weight gain and loss, I will just stick it to that there is a slight oxide layer while performing the experiment. Hence as the sodium carbonate reacts with the oxide layer, zinc carbonate will be formed?

By the way, regarding the equations,
Zn + Na2CO3 --> ZnCO3 + 2Na
is zinc carbonate as aqueous/solid?

Perito · Sep 28, 2009, 08:46 PM

Sodium carbonate will not absorb oxygen from the air. Water will absorb some carbon dioxide from the air and form carbonic acid, H2CO3. Maybe that's what people are confusing.

Zinc carbonate isn't very soluble, but it's not totally insoluble. It will partially precipitate. If the solution is acidic, the carbonate will form carbonic acid. Carbonic acid will dissociate into CO2 and H2O and the CO2 will bubble out of the solution (think soda pop).

melvados · Sep 28, 2009, 08:59 PM

Originally Posted by Perito

Sodium carbonate will not absorb oxygen from the air. Water will absorb some carbon dioxide from the air and form carbonic acid, H2CO3. Maybe that's what people are confusing.

Zinc carbonate isn't very soluble, but it's not totally insoluble. It will partially precipitate. If the solution is acidic, the carbonate will form carbonic acid. Carbonic acid will dissociate into CO2 and H2O and the CO2 will bubble out of the solution (think soda pop).

I see. Cause I am submerging the zinc and copper totally in sodium carbonate solution. No water is added unless the solution itself contains water.

By the way, is it possible if I ask about the mirco structure? Took some mircoscopic pictures of it and needs some clarification though...

Perito · Sep 29, 2009, 03:33 AM

I see. Cause I am submerging the zinc and copper totally in sodium carbonate solution. No water is added unless the solution itself contains water.

"Sodium carbonate solution" implies water.

By the way, is it possible if I ask about the micro structure? Took some microscopic pictures of it and needs some clarification though...

You can always ask. I used to do a lot of scanning electron microscopy. I might be able to answer some questions about that -- or maybe not.

melvados · Sep 29, 2009, 04:35 AM

Originally Posted by Perito

"Sodium carbonate solution" implies water.

You can always ask. I used to do a lot of scanning electron microscopy. I might be able to answer some questions about that -- or maybe not.

Okay. So since sodium carbonate solution implies that water is involved, then I can say that the water in the solution will absorb some carbon dioxide from the air and form carbonic acid, H2CO3, as said by you, Perito?

So if that's the case, can I also say that as carbonate acid is formed, the acid will also reacts with zinc, thus corroding it? (Cause I am doing a corrosion experiment on metals)

As for the microscopic scans, in its initial form (before experiment), say copper for example, there are a lot of line as I did not polished it well. But after the experiment and I took another scan, I saw a lot of black holes? Or pits, my friend says...

So the pits/black holes, what are they actually?

*Need me to attach a picture of it?

Unknown008 · Sep 29, 2009, 07:13 AM

Hey Perito. I was wondering... does that mean that in the reaction, you have copper and zinc oxides formed?

Originally Posted by Perito

2. Zinc will replace copper.

The oxide will give a weight gain, though it would be very small.

Copper forms an oxide layer fairly slowly compared to some other metals, and the oxide layer is not very thick or heavy. If you really wanted to be sure that it didn't oxidize, you'd have to clean it off under an inert atmosphere (argon or nitrogen) and use it in there. For most work, I would use steel wool to clean the oxide from the copper, and then I would weigh it and use if directly.

Zinc is more reactive than copper but I'd probably do the same for zinc as for copper.

I'm starting to doubt what all the teachers up to now have been teaching me and my friends... :(

melvados · Sep 30, 2009, 08:45 PM

I'm getting abit confused here :(

Perito · Oct 1, 2009, 05:03 AM

I was wondering... does that mean that in the reaction, you have copper and zinc oxides formed?

You'll most likely get the carbonates since the carbonates are the most easily formed. You will, no doubt, also get some hydroxides. If water is around, it's unlikely that you'll form oxides. If you dry the precipitates out, and then heat them up, the hydroxides will dehydrate to form oxides, and the carbonates will decompose to form CO2 and oxides.

Perito · Oct 1, 2009, 05:07 AM

[QUOTE]
Okay. So since sodium carbonate solution implies that water is involved, then I can say that the water in the solution will absorb some carbon dioxide from the air and form carbonic acid, H2CO3, as said by you, Perito?
[QUOTE]

Yes. This is a problem in some chemical analyses.

So if that's the case, can I also say that as carbonate acid is formed, the acid will also reacts with zinc, thus corroding it? (Cause I am doing a corrosion experiment on metals)

That's also correct -- to an extent. Water will also react with zinc and form a thin oxide shell on it -- much as it does with aluminum and magnesium. The oxide coat isn't as durable as aluminum oxide. If you put zinc under water, it will eventually corrode.

As for the microscopic scans, in its initial form (before experiment), say copper for example, there are a lot of line as I did not polished it well. But after the experiment and I took another scan, I saw a lot of black holes? Or pits, my friend says...

So the pits/black holes, what are they actually?

The pits are locations where the zinc has corroded or is corroding. I've seen this type of thing many times before.

melvados · Oct 1, 2009, 07:25 AM

Hi Perito, thanks for your prompt reply. There's a few things I like to ask about the pits.

1. Since you say that the pits show the locations of the zinc corroding/corroded, do you mean to say it's the metal itself?
(Its not the oxide layer or anything right?

2. Does the occurring of the pits happens in one direction or (there are straight/lamellar? Lines in the structure), or do they simply expand itself from the initial pits' location

Unknown008 · Oct 1, 2009, 07:32 AM

Originally Posted by Perito

You'll most likely get the carbonates since the carbonates are the most easily formed. You will, no doubt, also get some hydroxides. If water is around, it's unlikely that you'll form oxides. If you dry the precipitates out, and then heat them up, the hydroxides will dehydrate to form oxides, and the carbonates will decompose to form CO2 and oxides.

Thanks! I didn't mention any heating (nor I saw heating involved in the question) but it sure got me worried. I knew that some water would react with the metal. :)

melvados · Oct 1, 2009, 07:33 AM

Sorry, by the way how does the hydorxide gets into the picture? I mean how it is formed, can't really think this out...

Unknown008 · Oct 1, 2009, 07:39 AM

Ok, I know at least that one :)

$Metal + Water \rightarrow Metal\, Hydroxide+Hydrogen$

Right? Well, since there is water in the reagents, you catually have another reaction occuring:

$Zn + 2H_2O \rightarrow Zn(OH)_2+ H_2$

melvados · Oct 1, 2009, 07:43 AM

I see. Thanks a lot unknown008.

Well in these case, it seems like I'll be having a lot of equations just for zinc + sodium carbonate.
Hydroxides, carbonates, carbonic acid etc...

lol

Unknown008 · Oct 1, 2009, 07:53 AM

Yup, chemistry is about all these! :)

melvados · Oct 1, 2009, 07:55 AM

Haha that is right. I will post any questions if I run into one again. :)

Unknown008 · Oct 1, 2009, 08:00 AM

Wait, I hope you have seen that zinc does not react with sodium carbonate solution to give sodium and zinc carbonate!