[darknietzsche]

I have a problem for my Chemistry homework for my class, and I have been having some difficulties. It involves an unknown element X in a compound reacting with water and I have to determine the unknown element X using the information given.

Q: A compound with the formula XOCl₂ reacts violently with water, yielding HCl and the diprotic acid H₂XO₃. When .350g of XOCl₂ was added to 50.0 ml of water and the resultant solution was titrated, 96.1 ml of NaOH was required to react with all the acid.

Find the atomic mass and identity of element X?

This is what I know:

XOCl₂ + 2H₂0 ---> 2HCl + H₂XO₃

and

H₂XO₃ + 2NaOH ---> 2H₂O +Na₂XO₃

If someone can just show the math to get to the number of moles of
XOCl₂ which will allow you to get the molar mass of the compound. I may have messed up in the math somewhere, but when I did the calculations I got the mass of X to be negative and couldn't find my mistake.

[Borek]

Show your caculations so that someone can locate problem. Right now it is impossible to check/do anything, as NaOH concentration is not given.

[ARGOS++]

Dear DarkNietsche,

You may forgot, that you will also titrate the generated HCl and that means that :
      four mol NaOH is equivalent to only one mol of your H₂XO₃.

Now from the titration you should be able to calculate how much mol of Cl₂XO will weight 0.350g.
I think that the last step is not too difficult for you.
(I assume that concentration of NaOH is equal 1N.)

 
Good Luck!
                    ARGOS⁺⁺

[darknietzsche]

Sorry, the molarity of NaOH is .1225M.

[darknietzsche]

Okay, I have redid the math using the fact that four mol of NaOH = to one mol of H₂XO₃ and got a closer answer.

Num. of mols of NaOH= .0961L x .1225M= 1.177 x 10^-2 mols

1.177 x 10^-2 mols of NaOH X 1 mol of H₂XO₃/ 4 mols of NaOH= 2.94 x 10^-3mols

2.94 x 10^-3mols H₂XO₃ x 1 mol of XOCl₂/ 1 mol of H₂XO₃= 2.94 x 10^-3 mols of XOCl₂

molar mass= .350g/2.94 x 10^-3= 118.92 g/mol

118.92g- 35.45g x 2- 16.0g= Mass of element X or 32.02 g which is close to the mass of sulfur

This is my new math, and at least now I have an element. If this is incorrect, please correct the error.

[agrobert]

Look up thionyl chloride, do your reactions make sense for this highly reactive compound?  I think you answered your questions.  Your weight may be off due to rounded atomic masses.

[darknietzsche]

Yeah, your right. Thanks.