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

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 :)

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.

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?

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).

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...

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.

"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?

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


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... :(

I'm getting abit confused here :(

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.

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.

[QUOTE]
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.

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

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. :)

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

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

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

Yup, chemistry is about all these! :)

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

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

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

But isn't that the (actual) chemical equation for it?
Zinc + sodium carbonate will gives sodium + zinc carbonate?

By the way, the surface of the zinc looks dull/dark, is it due to the zinc carbonate?

That reaction is not possible! Perito already told you that. What really happens is that your zinc will react with the water and carbonic acid in the sodium carbonate solution.

You cannot have a less reactive metal displacing a more reactive one.

If that was the case, the sodium would immediately react with water in the solution, and forming sodium hydroxide.

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 occurrence 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

1. The dark pits are probably finely-divided metal shavings coated with hydroxide/oxide and metal hydroxide. In aqueous solution, it's unlikely that you'll form much oxide. Most of it will be zinc hydroxide. Finely-divided metal appears black. Pure zinc oxide is white.

2. Pits can be oriented in one direction, or they can be perfectly round. Corrosion is more prominent in metal that is under stress and when metal is "worked", it will often stress in one direction. Corrosion pits will then be elongated. In annealed zinc, it would be more likely to see fairly round pits.

Pitting and corrosion can also be a sign of impurities in the metal. Metallurgists spend a lot of time examining failed pieces to determine what caused the failure. Impurities ar often found as causes of failure. Impurities can weaken metal and they can accelerate corrosion.

Okay. Let me summarize to see if I am correct so far. Say zinc + sodium carbonate reaction, is it okay if I write out the following reactions as of below:

1. Na2CO3 + H2O --> HCO3 + OH + 2Na (Not very sure about this)
(Reaction of sodium carbonate with water I presume; As I am using sodium carbonate solution - 'implies there is presence of water'? forms hydrates?)

2. Zn + 2H2O --> Zn(OH)2 + H2
(Since there is water in the reagents, another chemical equation can be occurred, thus forming zinc hyroxide)

3. H2O + CO2 --> H2CO3
(water in the solution reacts with the carbon dioxide in the air, forms carbonic aci

4. H2CO3 + Zn --> ZnCO3 + H2
(Formation of carbonic acid reacts with zinc, forms zinc carbonate and hydrogen gas)
* Do I need to write out another equation about carbonic acid reacting with the zinc oxide if I assume there's an oxide layer?

Then supposedly, if the equation I wrote in step 1 is correct, will it be okay if I write this equation:
ZnCO3 + 2Na --> Zn + Na2CO3 ?
(To show that it will be more realistic, rather than I wrote Zn + Na2CO3 --> ZnCO3 + 2Na, as there is no way that zinc will produce sodium)

Okay. Let me summarize to see if I am correct so far. Say zinc + sodium carbonate reaction, is it okay if i write out the following reactions as of below:

1. Na2CO3 + H2O --> HCO3 + OH + 2Na (Not very sure about this)
(Reaction of sodium carbonate with water I presume; As I am using sodium carbonate solution - 'implies there is presence of water'?, forms hydrates?)

2. Zn + 2H2O --> Zn(OH)2 + H2
(Since there is water in the reagents, another chemical equation can be occurred, thus forming zinc hyroxide)

3. H2O + CO2 --> H2CO3
(water in the solution reacts with the carbon dioxide in the air, forms carbonic aci

4. H2CO3 + Zn --> ZnCO3 + H2
(Formation of carbonic acid reacts with zinc, forms zinc carbonate and hydrogen gas)
* Do I need to write out another equation about carbonic acid reacting with the zinc oxide if I assume there's an oxide layer?

Then supposedly, if the equation i wrote in step 1 is correct, will it be okay if i write this equation:
ZnCO3 + 2Na --> Zn + Na2CO3 ?
(To show that it will be more realistic, rather than I wrote Zn + Na2CO3 --> ZnCO3 + 2Na, as there is no way that zinc will produce sodium)

1. There are many separate equilibria involved. The pH of the solution and the concentration of the other solutes will determine exactly which species exist.

Na_2CO_3 + H_2O \rightleftharpoons Na^+ + NaCO_3^- \rightleftharpoons 2Na^+ + CO_3^{-2}

CO_3^{-2} + H_2O \rightleftharpoons HCO_3^- + OH^-

HCO_3^- + H_2O \rightleftharpoons H_2CO_3 + OH^-

H_2CO_3 \rightleftharpoons H_2O + CO_2

2. This equation will be driven to the right because the hydrogen that is formed will bubble out of the mixture.

Zn + 2H_2O \rightarrow Zn(OH)_2 + H_2(g) \uparrow

3. This also occurs. The pH of the solution determines how far to the right it will go. If the solution is basic, a lot of CO2 will be absorbed. The hydroxide ion (OH-) will react with H2CO3 to form H2O and HCO3- and CO3(-2). As in #1, above, all of the species will exist, but the exact amounts of them will depend on the solution pH and the amount of solute that is dissolved in the solution.

If you leave absolutely pure water in the air, the pH will drop from 7 to below 6 because CO2 is absorbed from the air.

H_2O + CO_2 \rightleftharpoons H_2CO_3

4. Remember that the hydrogen ion (H+) is the actual species that reacts with zinc.

2H^+ + Zn \rightarrow Zn^{+2} + H_2

Zn^{+2} + CO_3^_{-2} \rightleftharpoons ZnCO_3

The important thing to understand is that in solution, salts will dissociate into their respective ions. Sometimes the ions will react with each other to form insoluble species (that will drive the reaction; possibly to completion), and some species will leave the solution (that may also drive the reaction to completion).

Gases won't always leave the solution. There is always a finite solubility of a gas in a solution. Oxygen, for example, dissolves in water. If this weren't true, fish would die.

1. There are many separate equilibria involved. The pH of the solution and the concentration of the other solutes will determine exactly which species exist.

Na_2CO_3 + H_2O \rightleftharpoons Na^+ + NaCO_3^- \rightleftharpoons 2Na^+ + CO_3^{-2}



Thanks Perito, but mind explaining to me again for the above equation in the quote? Not quite able to understand it. Sorry for the inconvenience caused.

By the way, CO3 is carbonate right, just to confirm? And what is HCO3?

For the equation you quoted, the same thing applies. You have all these simultaneously. Na_2CO_3 dissociating into Na^+ and NaCO_3\,^-, and the NaCO_3\,^- dissociating into CO_3\,^{2-} and Na^+.

Yes, CO_3\,^{2-} is carbonate.

HCO_3\,^- is hydrogen carbonate, an ion between H_2CO_3 and CO_3\,^{2-} if you want.

It's the same as for the sulfuric acid, hydrogen sulfate and sulfate ion: H_2SO_4,\, HSO_{4}\,^-,\, SO_{4}\, ^{2-}

The carbonic acid dissociates into the H^+,HCO_3\,^- and CO_{3}\, ^2-

Thanks guys. Sorry fot the late reply. Finally I have understand how the equation works.

By the way just like to know something.
Metals reacts well with cold acid/alkaline or with hot acid/alkaline? If so why?

1. The dark pits are probably finely-divided metal shavings coated with hydroxide/oxide and metal hydroxide. In aqueous solution, it's unlikely that you'll form much oxide. Most of it will be zinc hydroxide. Finely-divided metal appears black. Pure zinc oxide is white.

2. Pits can be oriented in one direction, or they can be perfectly round. Corrosion is more prominent in metal that is under stress and when metal is "worked", it will often stress in one direction. Corrosion pits will then be elongated. In annealed zinc, it would be more likely to see fairly round pits.

Pitting and corrosion can also be a sign of impurities in the metal. Metallurgists spend a lot of time examining failed pieces to determine what caused the failure. Impurities ar often found as causes of failure. Impurities can weaken metal and they can accelerate corrosion.

Then Perito, for the darks pits you have said in the first paragraph, can I say that they are actually the signs of hyroxides/oxides, then other the rest of the structure seen will actually be the metal itself (w/o the darks pits color) as shown in the following picture?

http://i378.photobucket.com/albums/oo226/melvados/pits.png