# Getting the identity of an unknown element in a reaction.

1. Nov 28, 2004

### philistinesin

Hi.

I'm having a hard time solving this problem.

I have to find the identity of element X in the following reaction:

$$XCl_2~+~Cl_2~-->~XCl_4$$

knowing that 10 grams of $$XCl_2$$ + 2.55 grams of $$Cl_2$$ produces 12.55 grams of $$XCl_4$$.

Now, I thought about doing mass percent composition that way I could know how much Cl there was in relation to the element X but I don't know any way to do that.

I'm stuck. Any ideas?

Last edited: Nov 28, 2004
2. Nov 28, 2004

### chem_tr

You may try starting with the mole calculation of chlorine; it is 71 grams/mol. How many moles are there in 2.55 grams of chlorine gas, if one mole weighs 71 grams?

If we assume that all of this chlorine gas is reacted, then you will find how many moles of the unknown chloride along with the formed new chloride, and easily find the molar mass of X from there.

Note that if there is a deviation in calculating X in the first and second chloride, you may have to consider that the reaction did not proceed 100%.

3. Nov 28, 2004

### GCT

The reaction is in stoichiometric equivalence, the way you can tell is due to exact mass conservation: 2.55 + 10 = 12.55, thus there is no excess reagent.

Since all of the reactants and products are in the same mole to mole ratio, you can start with finding the realistic mole value of chlorine, this will be the realistic mole value of X.

The realistic value of X can be found simply by subtracting (2.55x 2.......you should know why) from 10. Now you should easily be able to find the molar mass.

Last edited: Nov 28, 2004
4. Nov 29, 2004

### philistinesin

Thanks to all for the help.