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Topic: identifying unknown compounds by mass relationships  (Read 11482 times)

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Offline ainoko_hikaru

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identifying unknown compounds by mass relationships
« on: July 05, 2008, 11:12:32 AM »
hello. i need some help with my chemistry. can you please help me?

i am asked to identify which unknown compound was used for an experiment by using mass relationships. all the compounds are salts. i have succeeded in knowing that the substance is a hydrogen carbonate. i am now choosing between NaHCO3 and KHCO3.  the problem is this:
       Write the chemical equation for the overall reaction that would occur when the original compound
        was converted to a chloride. If the compound is a hydrogen carbonate, use the sum of Equations
       1 and 2. If the sample is a carbonate, use Equation 2. Write the equation for a sodium salt and
        then for a potassium salt.

Equation 1 is ( for hydrogen carbonate, eg. NaHCO3(s) )
2 NaHCO3(s) --> Na2CO3(s) + H2O(g) + CO2

Equation 2 is ( for carbonate, eg. Na2CO3(s))
Na2CO3(s) + 2H(aq) + 2 Cl(aq) --> 2 NaCl(s) + H2(l)O + CO2(g)

I do not know how to use the sum of equations 1 and 2 so i can write a chemical equation. please help. thanks a lot! :)

i'm thinking that i should combine all the equations, but i just don't know where to start. i tried having the left side of equation 1 be added with hydrogen and chlorine that will result to NaCl, Na2CO3(s), water, and carbon dioxide. is this correct?

thanks!

~neo

Offline Borek

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Re: identifying unknown compounds by mass relationships
« Reply #1 on: July 05, 2008, 04:22:46 PM »
Most likely it simply asks to write equation of reaction between NaHCO3 and HCl. PLease note, that you should always put charge on ions when you list them (so not H(aq) but H+(aq)).
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Offline vhpk

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Re: identifying unknown compounds by mass relationships
« Reply #2 on: July 05, 2008, 11:02:24 PM »
If you write 2 equations and want to combine them into 1, the first to do is to find the coefficient of the substance which exists both in the left of this equation and the right of another. If they are equal, you can combine them like combining 2 normal mathematical expression. But if they are different, you must multiply this equation with the coefficient of another and versus then do the same thing above. This is essential for us when doing some complicated equation, I suppose. But this reaction is simple, then you only write the dissociation of 2 substances in solution then write the overal equation. Compare the acid- conjugated base pair of each of them to find the ultimate product.
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Offline ainoko_hikaru

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Re: identifying unknown compounds by mass relationships
« Reply #3 on: July 05, 2008, 11:06:51 PM »
ok, thanks a lot!

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