# A coordination compound is found by analysis to contain 21.79%Co 18.09%NH3 and 39.32Cl remainder is h2o empiri

find the empirical formula

If we just pretend we have 100g (a nice round number) of this material, then we can assume we'll have 21.79g of Co (Cobalt), 18.09g of NH3 (ammonia), 39.32g of Cl (chlorine), and the remaining 20.80g of H2O (water). That adds up to 100g, right?
So now if you have the formula weights of all of these things, we can figure out how many moles of each we have. Cobalt weighs 58.93 g/mole, so 21.79g is 21.79/58.93 = 0.37 moles of cobalt. If you do the same for the others, you get: 18.09/17.03 = 1.06 moles of ammonia, 39.32/35.45 = 1.11 moles of chlorine, and 20.80/18.015 = 1.15 moles of water.
Okay, so we have:
Co = 0.37 moles
NH3 = 1.06 moles
Cl = 1.11 moles
H2O = 1.15 moles
These ratios aren't perfect, but it looks like it's pretty much a 1:3:3:3 ratio. The inaccuracy can be due to impurities in the mixture, innacurate mass measurements, and/or significant digits used in the calculations. But assuming this is about right, you get a formula of CoCl3(NH3)3(H2O)3 ...the numbers should be in subscript.

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