How do you find this element?

Question

A compound is composed of element X and hydrogen. There is 80% X by mass, but there are 3 times of hydrogen atoms as X atoms per molecule. Determine element X.

So it's asking for element X, where there are 3 hydrogen molecule per X, but X still makes up 80%. Is it possible?

How can you find the empirical formula of XH3, if you don't know the molar mass of the element X?

Is it possible for someone to go through the problem step by step?

I'm trying to figure out the empirical formula, by dividing 20g of hydrogen with 1.00794g/mole, which I got 19.8425 as the answer. Then, do I divide that by 3?

Answer 1

You have all the information you need for figuring it out in the original statement.

First, what the mass breakdown tells us: the ratio of the unknown element's mass to the hydrogen's mass in the compound is 80% to 20% or 4 to 1. (By the way, this holds true whether we consider the entire sample or just one molecule so I will speak in terms of one molecule from here forward.)

Then we look at the information the number of atoms provides. We are told there are 3 hydrogen atoms in each molecule to 1 of the unknown element's atoms in each molecule (3 to 1).

We multiply these factors (you can think of it as cross-multiplying 1:3::4:1) and find that each of the unknown element's atoms masses 12 times as much as hydrogen atoms do.

So the molecule is: CH3 because anyone working in chemistry knows carbon is element 12 and that the standard mole weights are derived using that as a reference. (Convenient here because we don't have to find a periodic table and see which element is 12 as we better know that one!)

So the general process using this kind of information is write out the ratios consistently and cross-multiply.

Answer 2

It's certainly possible. You just need to find the element where 1/3 the number of atoms is 4 times the weight of the hydrogen atoms.

Answer 3

Yes it is possible, since the 80% is by mass, not by number!

Find empirical formula first (XH3), then figure out molecular formula.

I would multiply the atomic mass of H by 3 to find total mass of H in empirical formula. (1.00794 x 3 ~ 3)

This represents 20% of mass, thus the X is going to be 4 times that mass (4:1 ratio). that means that X is going to be 4* 3

Answer 4

its only possibal if the substance came out of my ***.