# Need to identify mysterious element

1. Mar 7, 2007

### jacker2011

1. The problem statement, all variables and given/known data
An element X forms both a dicholride( XCl2) and tetrachloride(XCl4). Treatment of 10.0g of XCl2 with excess forms 12.55g of XCl4. Calculate Atomic Mass of X and Identify X

2. Relevant equations
no equation needed...but urgent

3. The attempt at a solution

i try subtracting 12.55g of XCL4 with 10.0g of 10.0g of XCL2
and i am lost at what is the EXCESS, is that CL2 ?

if it is...then i have 2.55g/ 71g CL2 = 0.359mole of CL2. basically i am lost

2. Mar 7, 2007

### dextercioby

Do you get the equation

$$\frac{10}{x+71}=\frac{12.55}{x+142}$$ ?

3. Mar 7, 2007

### jacker2011

thank you, i never realize i just have to use cross multiply. i see ur work as x+CL2(71) = x+Cl4(142)