Question

What is the mass of oxygen in dimethylsulfoxide (`C_2H6SO`) rounded to three significant figures?

Answer 1

Well, how many oxygen atoms are there in 1 formula unit of `"DMSO"`? Clearly, there are 1.

Explanation:

And what is the mass of 1 oxygen atom? Clearly, it is `"16.0 amu"`; where `"amu "-=" atomic mass unit"`.

Chemists usually deal in molar quantities, where oxygen has an atomic mass of `16.00*g*mol^-1`.

If your teacher has set this question, he (or she) should be willing to show you some `"DMSO"`. It is an oily liquid that readily passes thru the skin. Because `"DMSO"` is a fairly powerful solvent, it takes anything on the skin across the skin barrier with it - if you dissolve an aspirin up in it, you can use the solution to apply topical relief to sprains and aches (and it is used in sports medicine for this purpose). The `"DMSO"` solvent is usually reduced to `"dimethyl sulfide"` in the body, `Me_2S`, which smells absolutely foul, and would give the user appalling bad breath.

Of course, sometimes a chemist might dissolve something like potassium cyanide up in `"DMSO"` to do a reaction. Why would this be a problem if the chemist got the solution on their bare hands?