Substance that will librate CO2

1. Sep 15, 2012

chikis

1. The problem statement, all variables and given/known data I have two questions:
(1) Suppose we have solution W, X, Y and Z. Their pH are 8, 12, 4 and 2 respectively, from the information given which of the solution W, X, Y and Z will liberate carbon (IV) oxide from trioxocarbonate (IV) salt?

(2) Between CaCO3 and CaO, which is best for making mortar?
I used to think that CaCO3 is good for making mortar simply because another name for it is lime stone which is used in making cement for building. Can CaO be used as well?

2. Relevant equations

3. The attempt at a solution
As question (1):
If you look at the pH scale, we know that acidity increases from 6 to 1 and 7 is neutral. In the other hand, basicity increases from 8 to 14. We all know that, acid react with trioxocarbonate (IV) salt to librate CO2. From the pH scale, we already know that substance Y and Z are acidic having a pH of 4 and 2 respectively. Because of this, Y and Z will librate CO2 from trioxocarbonate (IV) solution? But I still failed the test. Is there anything am missing?

As for question (2):
I used to think that CaCO3 is good for making mortar simply because another name for it is lime stone which is used in making cement for building. Can CaO be used as well?

2. Sep 15, 2012

chemisttree

This sounds like a trick question. Your analysis is correct but you are given a solution of pH 2 and 4. Sounds like any trioxocarbonate salt (absurd nomenclature, BTW) would have already liberated its CO2, yes? Can these solutions release any more carbon (IV) oxide? More absurd nomenclature for CO2, BTW! You have been punked by a stupid question so don't worry about it. Carbon (IV) oxide!!!! Give me a freaking break!

Another stupid question. Mortar is made with slaked lime (Ca(OH)2) not quicklime (CaO). Quicklime is used with special equipment only to make slaked lime for mortar or to stabilize expansive soils. If a mason were to use quicklime, he would burn his hands (they HATE that) and the mortar would heat and dry quickly adversely affecting bond strength. There are actually specifications keeping quicklime out of mortar and cements. Even hydrated lime is a bad actor in portland-type cement. Ground calcium carbonate is inert in cements and mortar and acts only as unreactive filler in those cases. Surprisingly, it is a fairly major component in some Type N and S mortars because it is cheap and easy to grind finely. Very misleading question unless you are studying mortars and cements in-depth.

3. Sep 15, 2012

chikis

So between CaCO3 and CaO, which do you think is best for making mortar?

4. Sep 15, 2012

chemisttree

Quicklime would be very bad in mortar. Using it to make slaked lime putty would be very good. Using finely ground calcium carbonate as an inert filler is acceptable for making mortar but you need slaked lime to make a mortar that will harden. Both are correct in some sense. Quicklime can't be used directly whereas ground lime can. In my mind that makes calcium carbonate most correct in this case.

It is a very misleading, poorly-worded question, IMO. The question should have been a choice between Ca(OH)2 and CaCO3 as a hardener in mortar.

5. Sep 15, 2012

chikis

I think what you are refering to as ground lime is CaCO3. Or is that not what you mean?

6. Sep 16, 2012

chemisttree

Yes, that is what I meant. I should have written 'ground limestone' in post #4.

7. Sep 16, 2012

chikis

I quite agree with you that this is a poorly worded question and that calciulm carbonate is the most fitting for making mortar.

8. Sep 16, 2012

chikis

Thanks for having intrest in my thread!