Question #7a65a

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Question #7a65a

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Answer 1 · 2016-08-31T11:00:42

Given that $1.41 \times 10^{22}$ $1.41xx10^22$ molecules of Styrene weigh $2.44 g$ $2.44g$ .We can write 1 mol or $6.03 \times 29^{23}$ $6.03xx29^23$ molecules of Styrene will weigh

$\frac{2.44 \times 6.023 \times 10^{23}}{1.41 \times 10^{22}} g \approx 104 g$ $(2.44xx6.023xx10^23)/(1.41xx10^22)g~~104g$

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

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

$Hence empirical formula of Styrene = C H$ $"Hence empirical formula of Styrene"=CH$

$Let its moleculr formula = {(C H)}_{n}$ $"Let its moleculr formula"=(CH)_n$

$So its molar mass from its MF becomes$ $"So its molar mass from its MF becomes"$
$= (12 + 1) n = 13 n \frac{g}{mol}$ $=(12+1)n=13ng/"mol"$

Hence we can write

$13 n = 104 \Rightarrow n = 8$ $13n=104=>n=8$

$So the molecular formula of Styrene$ $"So the molecular formula of Styrene"$

$= C_{8} H_{8}$ $=C_8H_8$

Answer 2 · 2016-09-01T12:51:01

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

Second Step:

To find $n$ $n$ number of atoms in each molecule we use Avogadro's number $6.023 \times 10^{23}$ $6.023xx10^23$
We know that $6.023 \times 10^{23}$ $6.023xx10^23$ molecules of any substance are equal to its $1$ $1$ gm mole.
It is given that $1.41 \times 10^{22}$ $1.41xx10^22$ molecules weigh $= 2.44 g$ $=2.44g$
$:.$ weight of $6.023xx10^23$ molecules $=2.44/(1.41xx10^22)xx6.023xx10^23$
$=104.22g$
Now weight of $"CH"=12.011+1.0079=13.0189$
$:.n=104.22/13.0189=8.005$
This gives us molecular formula of Styrene as $"C"_8"H"_8$
.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-

Styrene is also known as ethenylbenzene, vinylbenzene, and phenylethene. It is an organic compound and its chemical formula is $"C"_6"H"_5"CH=CH"_2$

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