Question on inorganic chemistry

[leena19]

Homework Statement

You are supplied with a mixture consisting of barium carbonate,dolomite,potassium carbonate and silicon dioxide.Explain how you would attempt to determine quantitatively each of the constituents present in this mixture

Homework Equations

The Attempt at a Solution

First I Weigh the mixture.

Then,since potassium carbonate would dissolve in water as all group 1 compounds are soluble, I first add water,and filter.The filtrate contains dissolved potassium carbonate,which I dry,weigh and calculate its % composition
To the residue I add HCl,so the SiO₂ remains which i later dry and weigh?
and in the filtrate I get CaCl₂,MgCl₂and BaCl₂.
I don't know how to proceed from here.I'm tempted to add NaOH,but then all 3 i.e,Ca(OH)2,Ba(OH)2 and Mg(OH)2 would precipitate,and I wouldn't be able to separate them?

Thank you

 

[Lok]

If wiki is right then dolomite means CaMg(CO3)2 that means echimolar conposition of the two. By weighing the rest after removal of Sio and KCO3 than a simple 2 unknowns equation will suffice.

 

[leena19]

I knew that dolomite was made of CaCO₃ and MgCO₃ but I didn't know they were each equimolar in composition,so thank you very much for that useful info.
Now I think I can manage to solve this problem easily if only I knew how to remove BaCO₃ from the mixture,without affecting the composition of dolomite.

I hope someone can help.

 

[Lok]

Is it necessary to remove each compound from the mixture or just to determine it's composition. Because in the case of the composition you already made enough transformations. You have the weight and the mole number of the CaCl2, MgCl2 and BaCl2 as you know how much HCl you reacted in the SiO2 separation.

 

[chemisttree]

http://www.mineralszone.com/minerals/dolomite.html" on a forum!

It occurs to me that you should research the solubilities of barium salts... and don't limit yourself to the chlorides.

 

[Lok]

http://www.mineralszone.com/minerals/dolomite.html" on a forum!

It occurs to me that you should research the solubilities of barium salts... and don't limit yourself to the chlorides.

Don't know where you are going with this as the mass % in the site still point to echimolarity of dolomite. Further separation is still not necessary.

 

[Borek]

Don't know where you are going with this as the mass % in the site still point to echimolarity of dolomite.

It doesn't. Equimolar is only an ideal case, real life samples don't have to be ideal.

In nature, considerable variations in the composition of dolomite relating to lime and magnesia percentages are found.

I am afraid question is unfortunate, as it is not necesarilly clear what to make of the 'dolomite' information - it means either 'equimolar mixture of Mg/Ca', or 'some mixture of Mg/Ca'.

 

[Lok]

If we question the purity of every compound ... then what is the point of it. Every step of the analysis will have it's tolerances.
Unless mass spectrometry or other means are present.

 

[Borek]

Dolomite is not a compound, dolomite is a mineral. Barium carbonate is a compound and nobody questions its purity. Minerals are rarely pure compounds.

 

[Lok]

Dolomite is not a compound, dolomite is a mineral. Barium carbonate is a compound and nobody questions its purity. Minerals are rarely pure compounds.

True to these words. This means that all reactions till now have to account for dolomite's impurities.

There is a limit to this so called helping process ... But I'll get you a beer someday Borek.

 

[leena19]

I don't really know what I should do really,cause

I've attempted another question related to dolomite(which I'm hoping i could solve after completiing this).In that question,it states"A large quantity of dolomite containing silica as the only impurity is provided" ,so I have a feeling they would have mentioned it if the sample was impure,but I'm not very sure

But I also feel that it may not be very accurate to take dolomite as an equimolar mixture of CaCO₃ and MgCO₃,

so I think its best to avoid the equimolar part and also to ignore any impurities found in dolomite cause afterall we're only asked to find quantitatively each of the constituents present(I could be wrong but we're not really asked to find the composition of MgCO₃ and CaCO₃ seperately right?i don't know if this is even possible but wouldn't it be just enough to find the mass of dolomite as a whole?or is this what you all have been saying so far?I can't really makeout what's going on :( )

It occurs to me that you should research the solubilities of barium salts... and don't limit yourself to the chlorides.

I researched and i don't know for sure but here's what I think,
To the chloride filtrate I obtained in my first post I add excess sulphuric acid.Then I get a precipitate of BaSO₄ which I filter ,dry and weigh and calculate the no. of moles which is equal to that of barium carbonate and in the filtrate I have MgCl₂/CaCl₂ ?
And since I now have the weights of potassium carbonate,SiO₂ and BaCO₃,I can substract their weights from the initial weight of the mixture to find the weight of dolomite,perhaps?