# Question #7a65a

Aug 31, 2016

Given that $1.41 \times {10}^{22}$ molecules of Styrene weigh $2.44 g$.We can write 1 mol or $6.03 \times {29}^{23}$molecules of Styrene will weigh

$\frac{2.44 \times 6.023 \times {10}^{23}}{1.41 \times {10}^{22}} g \approx 104 g$

$\text{Hence molar mass of Styrene"=104g/"mol}$

Now dividing given percentage composition C and H with their respective atomic masses we can have
$\text{The ratio of number of C and H atom in its}$
$\text{molecule} = C : H = \frac{92.26}{12} : \frac{7.74}{1}$
$= 7.69 : 7.74 \approx 1 : 1$

$\text{Hence empirical formula of Styrene} = C H$

$\text{Let its moleculr formula} = {\left(C H\right)}_{n}$

$\text{So its molar mass from its MF becomes}$
$= \left(12 + 1\right) n = 13 n \frac{g}{\text{mol}}$

Hence we can write

$13 n = 104 \implies n = 8$

$\text{So the molecular formula of Styrene}$

$= {C}_{8} {H}_{8}$

Sep 1, 2016

First step:
To find out the empirical formula of Styrene we divide the given percentages of its components by respective Average atomic masses.
$\text{Carbon":"Hydrogen} = \frac{92.26}{12.011} : \frac{7.74}{1.0079}$
$\implies \text{Carbon":"Hydrogen} = 7.68 : 7.68$
$\implies \text{Carbon":"Hydrogen} = 1 : 1$
We obtain Empirical formula of Styrene as $\text{CH}$
As such molecular formula is ${\text{C"_n"H}}_{n}$

Second Step:

To find $n$ number of atoms in each molecule we use Avogadro's number $6.023 \times {10}^{23}$
We know that $6.023 \times {10}^{23}$ molecules of any substance are equal to its $1$gm mole.
It is given that $1.41 \times {10}^{22}$ molecules weigh$= 2.44 g$
$\therefore$ weight of $6.023 \times {10}^{23}$ molecules $= \frac{2.44}{1.41 \times {10}^{22}} \times 6.023 \times {10}^{23}$
$= 104.22 g$
Now weight of $\text{CH} = 12.011 + 1.0079 = 13.0189$
$\therefore n = \frac{104.22}{13.0189} = 8.005$
This gives us molecular formula of Styrene as ${\text{C"_8"H}}_{8}$
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Styrene is also known as ethenylbenzene, vinylbenzene, and phenylethene. It is an organic compound and its chemical formula is ${\text{C"_6"H"_5"CH=CH}}_{2}$