# Question #99479

Oct 30, 2017

Carbon $\left(C\right)$

#### Explanation:

A "chloride" by definition is some compound with chlorine in it. So therefore, your mystery element and chlorine form a compound $X C l$ with molar mass $47.5 \text{g}$.

We also know that the molar mass of any compound is the sum of the molecular weights of its constituent elements. Therefore, we have:

${M}_{x} + {M}_{C l} = {M}_{X C l}$

The molar mass of $C l$ is $35.45 \text{g}$. Plugging that, along with the compound's molar mass, gives:

${M}_{x} + 35.45 = 47.5$.

Solving for ${M}_{x}$ is now simple:

${M}_{x} = 47.5 - 35.45 = 12.05 \text{g}$

If you look on a periodic table, you'll see that that molar mass is closest to that of carbon. So carbon is your mystery element.

However, $\text{C} C l$ is not a compound that exists. $\text{C} C {l}_{4}$ does, but not $\text{C} C l$. So either this question has assumed a made-up compound, or the problem statement has an incorrect molar mass. Regardless, this is the process you would follow.

What if you had to take into account the possibility of multiple $C l$ atoms, or even multiple atoms of they mystery element, in the compound? Well, then you'd need to at least be given a generic formula (ex.${X}_{2} C {l}_{4}$) in order to solve.

Hope that helps :)