[owlpower]

A student treated 1.385 g of an unknown metal M with excess HCl (aq).

M + x HCl —> x/2 H2 + MClx.

A gas evolved and it had a volume of 382.6 mL at 20 °C and generated 755 mm Hg pressure. He then heated the mixture to evaporate the water and remaining HCl and got a white crystalline powder MClx. Afterwards he dissolved the compound in 25.0 g of water and noticed that the melting point of the resulting solution was -3.53 °C. What is the molality of the solution and what is the value of X? (Given Kf of water = 1.86)

I have no trouble finding the molality, which is 1.897 mol/kg.
I am lost trying to get a whole number value for X. I determined X to be 2/3, but no matter how I manipulate (multiplying whole equation by constants, etc), I keep getting 2/3 for X. I can't see how I can force it to be a whole number (I'm guessing X = 2)

If it helps, one of the equations I got was : 1.5 M +  HCl —> 0.5 H2 + 1.5 MClx.

[Borek]

I have no trouble finding the molality, which is 1.897 mol/kg.

The number is OK, but that's not molality of the solution. Hint: van 't Hoff.