Posted by Sam on Saturday, July 24, 2010 at 4:36am.
What is the formula mass of ammonium phosphide, (NHsubscript4)subscript3P?
85.0 u
49.0 u
48.0 u
57.0 u
I thought I was to look these up in the Periodic Table, but they aren't there, so I'm confused on what to do. Any help would be appreciated.

Chemistry  DrBob222, Saturday, July 24, 2010 at 12:46pm
You DO (REALLY DO) look them up on the periodic table. The periodic table lists elements, not compounds, so you look up the elements and add them.
(NH4)3P. Here are the approximate values but you need to confirm them and make them more exact. I've just used whole numbers.
N = 14 x 3 of them = 42
H = 1 x 12 (that's 4 x 3) of them = 12
P = 31 x 1 of them = 31
Now add 42 + 4 + 31 = formula mass (NH4)3P