[willpfc]

Hi, Pls cud u help me solve this question and tell me how to work it out.Thx

22.5% of the mass of a sample of phosphorus chloride is phosphorus.
What is the formua of phosphorous chloride? (A_r values: P=31, Cl=35.5)

[ARGOS++]

[mahar.sean]

     l am going to venture a guess, an relatively uneducated one, that you should pay attention to the word "mass".  Mass is not weight, which creates problems with using molar values.  You may need to change the mass to weight using: w=mg. Weight equals mass times acceleration due to gravity, which if I recall correctly can be stated as 9.8 meters per second squared.  Unfortunately I have forgotten the units for mass.
     Please excuse me if I am erroneous, I have the intent to help.

[Arkcon]

It is a little sloppy, to be sure, but chemists do use the term molecular mass and molecular weight, as synonymous.  This is not to say, that an item's weight and mass are equivalent. 

FWIW, the SI units for mass is actually, grams.  Since weight is defined as mass times force of gravity, we use, IIRC, newtons.  Recently, I mentioned in another thread, for those stuck in the Imperial measurement system, lbs. is the units for weight, the units for mass, is the slug.  Which I always found really funny. 

But all this has no bearing at all, on the original problem.

[mahar.sean]

Argos;
     I forgot that the problem can be solved independent of units when percentages are involved.  Thank you for helping willpfc, where I may have just confused the matter.