How do I work out a formula or molecular mass?

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How do I work out a formula or molecular mass?

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Answer 1 · 2016-04-04T18:45:45

For a start, you need a Periodic Table; then you need a formula to calculate; I'll use $U F_{6}$ $UF_6$ .

Explanation:

The Periodic Table tells me that $Avogadro's number$ $"Avogadro's number"$ of uranium atoms has a mass of $238.03 \cdot g$ $238.03*g$ , and that such a quantity of $F$ $F$ atoms has a mass of $19.00 \cdot g$ $19.00*g$ . In every exam of Chemistry and Physics you ever sit, you will and must be supplied with a Periodic Table.

What is $Avogadro's number$ $"Avogadro's number"$ ? It is simply $6.022140857 \times 10^{23}$ $6.022140857xx10^23$ individual items of stuff, here atomic nuclei. So to get the mass of a mole, $Avogadro's number$ $"Avogadro's number"$ of $U F_{6}$ $UF_6$ , I simply make the calculation $(238.03 + 6 \times 19.00) \cdot g \cdot m o l^{- 1}$ $(238.03+6xx19.00)*g*mol^-1$ . Formulae such as $N a C l$ $NaCl$ , $C a C O_{3}$ $CaCO_3$ , $C O_{2}$ $CO_2$ , $F e {(N O_{3})}_{2}$ $Fe(NO_3)_2$ , are calculated in precisely the same way. Get the atomic molar masses (from the Periodic Table, no-one expects you to remember them!), and sum the atomic masses correctly and appropriately.

This video will show you how to calculate the molar masses of two compounds, $S i O_{2}$ $SiO_2$ and $M {g (O H)}_{2}$ $Mg(OH)_2$ .

Hope this helps!

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How do I work out a formula or molecular mass?

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