[pomalidomide]

Question: When a particular metal X reacts with HCl, the resulting products are XCl₂ and H₂. Write and balance the equation. When 78.5g of X reacts completely, 2.42g of hydrogen gas results. Identify the element X.

How do I solve this question? I've balanced the equation and it is X + 2 HCl  →  XCl₂ + H₂. The answer is Zinc and I am completely lost as to how one can derive Zinc from this equation... I just started on stoichiometry btw. Thanks a lot!

[DrCMS]

How many moles of hydrogen gas is 2.42g?
How many moles of X give that many moles of hydrogen?
With the given weight of X and the calculated number of moles of X now calculate the molecular weight of X.

[pomalidomide]

How many moles of hydrogen gas is 2.42g?

2g of H₂ = 2 mol
2.42g of H₂ = 2.42 mol

How many moles of X give that many moles of hydrogen?

Since the balanced equation states that 1 mol of X produces 1 mol of H₂, it would be 2.42 mol of X that gives 2.42 mol of H₂.

With the given weight of X and the calculated number of moles of X now calculate the molecular weight of X.

This is where I'm stuck. If 2.42 mol of X is 78.5g, 1 mol of X is 32.44g(4s.f) which is not an element at all... agh am I doing something wrong here?

[AWK]

2.42 g of hydrogen is not equal to 2.42 moles of hydrogen molecules.

[pomalidomide]

Oops! Thank you for pointing that out, 2.42g of hydrogen would be 1.21 mol since 1g is 0.5 mol. I got the final weight of 64.876g which is close to zinc's molecular weight but my periodic table states that the molecular weight of zinc is 65.4g. Did something go wrong somewhere, again?

Edit: Figured it out. It's because my periodic table states that the molecular weight of hydrogen is 1g and not 1.008g.

[AWK]

78.5*H2/2.42 = 65.38855≈65.4

[pomalidomide]

Thank you! Means a lot to me.

[Borek]

I got the final weight of 64.876g which is close to zinc's molecular weight but my periodic table states that the molecular weight of zinc is 65.4g. Did something go wrong somewhere, again?

Experimental data is never exact, rounded data is never exact, so you should never expect exact numbers, they will be just close enough.