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How many atoms of Lithium are there in 14.3 grams of Lithium Fluoride? I can't seem to single out how many atoms of Lithium are in lithium fluoride.

I know that the first step is to convert 14.3 grams to moles, so 14.3 multiplied by the molar mass of LiF divided by 1 is 0.55 moles. But where do I go after this? Do I just multiply 0.55 by Avogadro's number?

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Convert 14.3 grams of Lithium Fluoride to moles which is the same for lithium and lithium fluoride since there is one atom of lithium per molecule of lithium fluoride (carry an extra significant digit to round later to 3 significant figures).

$\mathrm{moles(Li) = \dfrac{g(LiF)}{mw(LiF)} = \dfrac{14.3}{25.939} = 0.5513\text{ }moles(Li)}$

Convert moles to atoms by multiplying with Avogadro's number, and round to 3 significant figures.

$\ce{atoms(Li) = moles(Li)\text{ }(N_{a})} \mathrm{ = 0.5513(6.022E23) = 3.32E23}$

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no of moles in 14.3 g of LiF is

14.3*(1/formula unit mass)=no: of moles

no:of Li atoms=avogadro number * no:of moles (as in one LiF molecule there is only one Li ion)

the answer is 3.312*(10^(23)) (approximate value)

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  • $\begingroup$ Your answer has too many significant figures and it is a bit off. What did you use for the molecular weight of lithium fluoride and Avogadro's number?!? $\endgroup$ – MaxW Mar 13 '16 at 4:14
  • $\begingroup$ @MaxW i never intended to do the calculation.I just took the rounded of values for atomic mass.like a 19 for Fluoride and 7 fo lithium.(after all there is no point in doing the pin point calculation like even you can add the mass of electron too (which i don't think is needed when one explains the theory part). $\endgroup$ – Abhishek Pallippara gopakumar Mar 13 '16 at 6:47
  • $\begingroup$ I tried a number of variations in the values and couldn't get your answer. I just don't think you should say "the answer is" if you haven't done a proper calculation. $\endgroup$ – MaxW Mar 13 '16 at 6:54
  • $\begingroup$ @MaxW thats a valid point which i missed out(didn't add "approx").well i will edit.Thanks $\endgroup$ – Abhishek Pallippara gopakumar Mar 13 '16 at 6:56

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