# Why do we assume that it is 1 mol?

A question in my book was as following:

Benzine and chloroform are considered very toxic organic solvents that dissolve in each other and in a solution of benzine and chloroform there is 0.45 mol of benzine. Find the the percent of mass( percent concentration solutions) in this solution.

In the answer, It assumed that the number of moles in the solution is 1 mole then subtracted 0.45 to get the number of moles of chloroform.

Why did he do that? Why specifically 1? It will obviously change if I assume any other number. (Unless I multiply the number of moles of benzine by that number) Or should we just say that for every a certain amount of moles of that solution has a percentage and every other percentage is right if it follows the same instructions?

• Can you update this question? "There is 0.45 mol" 0.45 mol of what? of total solution? 0.45 mol benzene? 0.45 mol chloroform? And what "percent of mass" do you want? Without knowing any of this, my guess is that 0.45 is the mole fraction of one of the solvents. Choosing the total number of moles to be 1 just makes the calculations easier, but you could choose any n and get the same result – Sean Doris Feb 26 '16 at 19:27

• The question is lacking some details, but in general, you can solve problems of this kind without stipulating any amount of moles. You can just call it $x$, and after doing calculations, you can find the ratio between the two substances in such a way that the $x$ cancels out. – Nicolau Saker Neto Feb 26 '16 at 21:20