The molecular formula for the provided composition of different elements is C₆H₁₄N₄.
Every time a problem provides you with a compound's molar mass, you can use a little trick to help you determine the compound's molecular mass faster.
More specifically, instead of determining the empirical formula first, then using the molar mass to get the molecular formula, we can skip the empirical formula altogether.
As you know, a compound's molar mass tells we what the mass of one mole of that substance is. In this case, one mole of our compound has a mass of 142.00 g . This means that if we pick a sample of 142.00 g of this compound, w can use its percent composition to get the exact number of moles of each element you get per mole of compound.
So, we know that this compound's percent composition is as follows:
carbon ---> 50.7%
Hydogen ---> 9.9%
Nitrogen ---.> 39.4%
This means that it contains
142 g of compound × 50.7 g of carbon / 100 g of compound = 71.99 g of Carbon
142 g of compound × 9.9 g of hydrogen/ 100 g of compound = 14.05 g of hydrogen
142 g of compound × 39.4 g of nitrogen/ 100 g of compound = 55.94 g of nitrogen
Now all we have to use the molar masses of
hese three elements to determine how many moles of each we get in one mole of our compound.
For carbon (C) : 71.99 g × 1 mole of C / 12.01 g
= 5.99 ~ 6
For Hydrogen (H) : 14.05 g × 1 mole of H / 1.007g
= 13.95 ~ 14
For Nitrogen (N) : 55.94 g × 1 mole of N / 14.006 g
= 3.99 ~ 4
therefore, molecular formula of compound will be C₆H ₁₄N₄ .
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