We could write: The reason conversation factors work so well in chemistry is tha

Question

We could write: The reason conversation factors work so well in chemistry is that chemical substances have fixed ratios of elements. This is expressed in chemistry using chemical formulas. For example, carbon monoxide is iron (III) nitrate is ammonia is, and phosphoric acid is the idea is that once we know that name of a substance we also know its formula, and once we know that, we can start working with it in the lab and be able to figure out how much of it we need to measure out. Now, it's not very convenient to measure out individual atoms or even dozens of molecules, so instead we resort to the idea of a "mole" which is roughly 6.022 times 10^23 of anything. Every substance has a name, a formula, and a "molar mass." Say we wanted 2.5 mmol of sodium and all we had was a bottle of sodium sulfate. Then we would calculate the number of mg of sodium sulfate we needed as follows:

Explanation / Answer

Sodium sulfate = Na2SO4

Na2SO4 ------------> 2Na + S + 4 O

1 mol Na2SO4 ---------> 2 mol Na + 1 mol S + 4 mol O

1 mol Na2SO4 ---------> 2 mol Na

1 mmol Na2SO4 ---------> 2 mmol Na

0.142 mg ------------------> 2 mmol Na [ Molar mass of Na2SO4 = 142 g/mol]

? ----------> 2.5 mmol Na

Then,

? = ( 2.5 mmol Na/ 2 mmol Na ) x 0.142 mg Na2SO4

   = 0.1775 mg Na2SO4

Therefore,

we need 0.1775 mg of Na2SO4

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