A Chemical reaction... (1 Viewer)

[Aerlinn]

Magnesium Carbonate is reacted with concentrated hydrochloric acid and the reaction goes like this:

MgCO3(s) + 2h20(l) ---> MgCl2(aq) + H2CO3 (aq)

My first query is, why is H2CO3 not a solid, since compounds with CO3(²-) (in brackets is the charge on the ion) are generally insoluble...?

My second query is, why does Magnesium Carbonate reacted with hydrochloric acid not produce an acid reaction like this:

MgCO3(s) + 2h20(l) ---> MgCl2(aq) + CO2(g) + H2O(l) ...?

If someone can help with this, it'd be great!

 

[xiao1985]

first of all, hydrochloric acid is HCl , not H2O

2ndly, yes, most carbonates are insoluable... but there are exceptions, namely group 1 carbonates, ammonium and in particular hydrogen carbonate... (aka carbonic acid, aka the stuff which makes your soft drink fizzles)

3rdly, it does... just that carbonic acid undergoes an equilibrium with CO2 gas and H2O liquid

 

[Aerlinn]

K, thanks
The HCl thing was a typo, must've copied the typo onto the 2nd equation too.
Your second point... are all group I carbonates soluble then, or only some?
Your third point... So if I'd written the 2nd equation, would it also be right? Can you explain that the equilibrium process you mentioned? I'm sorta bad with this, I'm trying to go through the stuff I'm about to learn... >.<

 

[xiao1985]

i'd prefer not to teach you equilibrium here... not because i'm slack, but it's a rather confusing concept, and usually it yields more questions than answers, and it's much better learnt in a systematic manner... (ie, visit your teacher/other friends who did it/older sis or bro who did chem and get them to explain it to you)

also, good to remember: all group I, NH4 +salts, and H+ salts are soluable in water

 

[Aerlinn]

Well, I know the concept of equilibrium, but only roughly. Can you write up an equation or something for when

carbonic acid undergoes an equilibrium with CO2 gas and H2O liquid

?
And I meant, are 'all group I carbonates soluble or only some'? Heh, prone to typos.

 

[xiao1985]

all group I salts are soluable... group I carbonates are salts... does that answer your question?! =p

ok for the equilibrium:

H2O (l) + CO2 (g) <---> H2O (l) + CO2 (aq) <---> H2CO3 (aq)

 

[Aerlinn]

Ah, ok. I can be a little slow at times xD

As for the eqillibrium, I could shower you with a million more questions, but I won't. Only this
If I wrote:
MgCO3(s) + 2HCl(l) ---> MgCl2(aq) + CO2(g) + H2O(l)
instead of:
MgCO3(s) + 2HCl(l) ---> MgCl2(aq) + H2CO3 (aq)
or vice versa...
Would they technically be the same answer and would I be counted wrong if I wrote one instead of the other...?
------------------
A thought: by group I 'salts' do you mean that all group I phosphates, sulfides, etc are all soluble? I probably sound dumb, but are OH-, SO4(²-), NO3 (-), Na+, K+, etc all salts... what IS a salt...?

 

[xiao1985]

a salt is an ionic substance... and you are absolutely right... group I chlorides, sulfates, nitrates, phosphates etc etc are soluable...

as for first question, there's no preference, but personally, i like 2nd eqn better... because H2CO3 gives ppl the impression that it will further undergo an equilibrium to form water and CO2... having CO2 and H2O just ain't that obvious...

 

[Aerlinn]

kk How do you tell whether things undergo further equilibrium, though...

 

[xiao1985]

you will learn some most (in)famous equilibrium very soon... but really, EVERY chemical equation technically undergoes equilibrium... just most reaction goes SO much to completion, that effectively there are no equilibrium present...

 

[Aerlinn]

Hmmm, I thought that most chemical reactions don't proceed to completion?

 

[xiao1985]

Hmmm, I thought that most chemical reactions don't proceed to completion?

take combustion of wood (celluose) for example... it's definitely a chemical reaction... and it's so entropically (and enthalpically ) favourable such that it pratically goes to completion (ie, you don't see some burnt wood turn back to unburnt wood do you?!)

 

[Aerlinn]

Heheh, then i think it's safer to say some reactions go to completion and some... don't

 

[xiao1985]

Heheh, then i think it's safer to say some reactions go to completion and some... don't

ok =)