Question #4bd23

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Question #4bd23

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Answer 1 · 2015-01-04T17:57:43

The empirical formula is $C H$ $CH$ . The molecular formula is $C_{6} H_{6}$ $C_6H_6$ .

Write down the ratio of the elements by mass.

%C = 100 - 7.74 = 92.26.

Ratio C : H by mass:

C : H = 92.26 : 7.74

To get the ratio by moles we divide by the $A_{r}$ $A_r$ values:

$A_{r} C = 12$ $A_rC=12$
$A_{r} H = 1$ $A_rH=1$

Ratio C : H by moles:

$\frac{92.26}{12} : \frac{7.74}{1}$ $(92.26)/(12):(7.74)/(1)$

= $7.69 : 7.74$ $7.69:7.74$

Dividing through by 7.69 we get:

1 : 1.006 which we can round down to:

1 : 1

So the empirical formula is $C H$ $CH$

To find the molecular formula we find how many $M_{r}$ $M_r$ units of $C H$ $CH$ will fit into the $M_{r}$ $M_r$ of benzene.

$M_{r} C H = 12 + 1 = 13$ $M_rCH=12+1=13$

$\frac{78.1}{13} = 6$ $(78.1)/(13)=6$

So the molecular formula is $C_{6} H_{6}$ $C_6H_6$ .

Answer 2 · 2015-01-04T18:10:35

The empirical formula is ${(C H)}_{n}$ $(CH)_n$ and the molecular formula is $C_{6} H_{6}$ $C_6H_6$ .

Since we know that a hydrocarbon only contains carbon and hydrogen, we can use the percent of hydrogen given to determine how much carbon the compound contains

$% carbon = 100 % - 7.74 % = 92.26 %$ $%"carbon" = 100%-7.74% = 92.26%$

The next step in determining the empirical formula is to divide each element's percentage by its atomic mass

$For C : \frac{92.26 %}{12.0} = 7.69$ $"For C": (92.26%)/12.0 = 7.69$

$For H : \frac{7.74 %}{1.00} = 7.74$ $"For H": (7.74%)/(1.00) = 7.74$

You then divide each of these two numbers by the smallest one to get the ratios of the two elements in the molecule:

$For C : \frac{7.69}{7.69} = 1$ $"For C": 7.69/7.69 = 1$

$For H : \frac{7.74}{7.69} ≅ 1$ $"For H": 7.74/7.69 ~= 1$

This is your empirical formula: ${(C H)}_{n}$ $(CH)_n$ - the ratio between carbon and hydrogen atoms is $1 : 1$ $1:1$ . We now have to determine how many of each the molecule contains.

This is done by using benzene' molar mass to determine the value of $n$ $n$ :

$78.10 = (1 \cdot 12.0 + 1 \cdot 1.00) \cdot n = 13.0 \cdot n$ $78.10 = (1 * 12.0 + 1 * 1.00) * n = 13.0 * n$

$n = \frac{78.10}{13.0} = 6$ $n = 78.10/13.0 = 6$

Therefore, your molecular formula is $C_{6} H_{6}$ $C_6H_6$ .

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Question #4bd23

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