Dr Collins Empirical Formula question

[DagS132]

Didn't find a thread for this exact problem. And hopefully I am placing this thread in right area.

Anyway, the question asks for empirical formulas. One of which is ammonium nitrite (NH4NO2). The answer stated by the review is NH2O which doesn't make sense to me since I am assuming this is an ionic bond between two polyatomic ions. Another example was sodium sulfate (Na2SO4) where the answer was Na2SO4. How come for ammonium nitrite it doesn't treat each of the two polyatomic ions as a single unit where as in sodium sulfate the polyatomic ion is treated as a single unit?

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[NextStepTutor_4]

That's a good question, @DagS132 . The answer is that bonds and positioning don't matter for the empirical formula. If we chopped up this molecule, we'd be left with 2 N atoms, 4 H atoms, and 2 O atoms, or a ratio of 1:2:1. In this example, the empirical formula was written in the same order as the parent molecule, starting with N, then H, then O: NH2O.

One reason we might be interested in this is because say we performed a chemical reaction and analyzed the product, and determind that the product contained a certain mass of N, a certain mass of H, and a certain mass of O. Using their molecular weights, we could figure out the molar ratios between them (for every one mole of N, there are two moles of H and one mole of O). This doesn't tell us anything about connectivity, however.

The empirical formula for Na2SO4 is Na2SO4 because if we break this down, there are 2 Na atoms, 1 S atom, and 4 O atoms. If we write these atoms in the same order, we have Na2SO4.

 

[DagS132]

Ah okay. That makes much more sense now. Thanks for your answer and time.