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Chemical Formulas

  1. Nov 5, 2004 #1

    Is there any systematic way to write chemical formulas??? Any help would be greatly appreciated
  2. jcsd
  3. Nov 5, 2004 #2
    Hello, first cation and then anion is written; this is a very general rule.
  4. Nov 5, 2004 #3


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    Maltun is right. First read the positive ion (cation), and then the second. But you will need some information about how special cations and anions are read, for example, [itex]NO_{3}^{-}[/itex] is read as nitrate.

    Let me give some examples on this:
    In the last example, remember that calcium ion has 2+ charge while phosphate is a 3- charged ion; so the smallest common number of these is 6.
    There are some exceptions where we don't obey the rule "cation first, anion second", as in acetate compounds. Potassium acetate is written as [itex]CH_3COOK[/itex] but we may rewrite this as [itex]KOOCCH_3[/itex], which is not a familiar style.

    I may go on if you need some more examples.
  5. Nov 7, 2004 #4
    I am sorry. I meant is there any systematic way to balance chemical equations. Right now we are learning how to do that.

    Any help would be appreciated!

  6. Nov 7, 2004 #5


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    Mostly it's a kind of trial and error approach. Depending on the equation, there may be a best way to gp about balancing it. If there is a certain radical that is present in only one species on either side of the equation, it's a good idea to start with that radical and balance it first. From there, the rest will fall into place relatively easily.

    If you show us with some examples, how you would balance certain specific equations, we might be able to tell you if you're doing it okay, or if there's a better way.
  7. Nov 7, 2004 #6
    Fe(OH)3 (s) + H2SO4(aq) ----------> MgSO4(aq) + (NH4)2S
  8. Nov 7, 2004 #7


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    Are you sure your reaction is correct? Or you've found some nuclear technique :smile:

    Iron(III)hydroxide is a base, and reacts with sulfuric acid to give its sulfate with water:

    [tex]2Fe(OH)_3+3H_2SO_4\longrightarrow Fe_2(SO_4)_3+6H_2O[/tex]
  9. Nov 9, 2004 #8
    True...and it's usually pretty easy. However, if it's a re-dox reaction, trial and error can be really time consuming. For those, you use "half reactions." That technique is quite systematic. Here's a simple example:

    To balance KClO4 + Al -> KCl + Al2O3, start by writing equations for the transfer of electrons that occurs with the elements that change in oxidation state:

    Cl(+7) + 8e -> Cl(-1)
    Al - 3e -> Al(+3)

    Now, find coefficients to multiply each equation by, so the total number of electrons going one way is equal to the total number going the other:

    3Cl(+7) + 24e -> 3Cl(-1)
    8Al -24e -> 8Al(+3)

    Put those numbers in the original equation:

    3KClO4 + 8Al -> 3KCl + 4Al2O3

    It gets a little messier when the reaction occurs in acidic or basic solution, but the general method is still the same.
  10. Nov 9, 2004 #9


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    A good explanation, congrats. It can be better if you learn and use LaTeX, but it is still okay now.
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