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Help with a chemical equation please

  1. Dec 25, 2011 #1
    Hi i'm new on here and a mature student studying geology. We have an assignment (our 5th one) to be in on the 11th jan . I'm in my 1st yr and have not ever studied chemistry unless you count a couple of years around the age of 11 or 12 which was now roughly 28 yrs ago!

    Anyway i've been trying to balance this equation for days but have a feeling that it may have been written incorrectly. If anyone would be kind enough to take a look and see if it can be done I would certainly appreciate it. Not particularly looking for the answer just to know if it can or can't be done.


    (d) Ca3Al2SI3O12(s) + H2CO3(l) + H2O(l) → Ca2+
    (aq) + Al4Si4O10(OH)8 (s)+ H4SiO4(l) +
    HCO3 -
  2. jcsd
  3. Dec 25, 2011 #2


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    Staff: Mentor

    I guess first substance on the left is an aluminosilicate, and the equation looks like this:

    Ca3Al2Si3O12 + H2CO3 + H2O -> Ca2+ + Al4Si4O10(OH)8 + H4SiO4 + HCO3-

    The way you wrote it it contained S and I - sulfur and iodine - instead of Si. As obvious typo, either done when you copied the equation or in the assignment.

    If so, it can be balanced. I would start assuming there is just a single molecule of Al4Si4O10(OH)8 produced - this is a standard procedure, select the most complicated compound and assume coefficient of 1.

    Often best approach to such monsters is the algebraic method of balancing chemical equations.

    Note that for the equation to be balanced, not only atoms have to be balanced, but also charges - which immediately means that on the right coefficient at Ca2+ must be half of the coefficient at HCO3-. In other words Ca(HCO3)2(aq) is the product, not two separate ions.
  4. Dec 25, 2011 #3
    Thanks did'nt expect a reply today, but will take your advice on board and have another crack at it , although that probably won't happen until all the turkey and wine has been finished. Many thanks and a merry christmas to you.
  5. Dec 25, 2011 #4
    Hey Thanks decided to have a go and just balanced it , think its this

    Ca3Al2Si3O12 + 6H2CO3 + H2O -> 3Ca2+ + 0.5Al4Si4O10(OH)8 + H4SiO4 + 6HCO3-

    Seems to be correct, I had'nt realised the coefficient on the charged ions needed to be that way, but it makes sense. You've made my christmas. Thanks again.
  6. Dec 25, 2011 #5


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    Staff: Mentor

    Please note you should multiply everything by 2 - coefficients should be the smallest possible integers.
  7. Dec 25, 2011 #6
    Ok Thanks, but i was told by my chemistry lecturer that we were fine using fractions so i will submit it like that and see what feedback i get.

    But thanks again for your help.
  8. Dec 25, 2011 #7


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    Staff: Mentor

    Fractions are OK during balancing and during stoichiometric calculations, where it is the ratio of coefficients that matters. However, thermodynamic values (like equilibrium constants) related to reactions are always listed assuming coefficients form a set of smallest possible integers. It is just a convention, but ignoring it you risk a nasty surprise one day. Following it always just puts you on the safe side.
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