Chemistry, 19.02.2020 20:44 coryowens44

Chemical analysis of an organic compound found the following composition: 40.0% C, 53.5% O, and 6.7% H. If the molar mass is 180.2 g/mol, how many empirical formula units are there in the molecular formula?

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Answer from: marbuigues9171

To form the molecular formula, we need 6 units of empirical formula

Explanation:

We are given:

Percentage of C = 40.0 %

Percentage of O = 53.5 %

Percentage of H = 6.7 %

Let the mass of compound be 100 g. So, percentages given are taken as mass.

Mass of C = 40 g

Mass of O = 53.5 g

Mass of H = 6.7 g

To formulate the empirical formula, we need to follow some steps:

Step 1: Converting the given masses into moles.

Moles of Carbon = $\frac{\text{Given mass of Carbon}}{\text{Molar mass of Carbon}}=\frac{40g}{12g/mole}=3.33moles$

Moles of Hydrogen = $\frac{\text{Given mass of Hydrogen}}{\text{Molar mass of Hydrogen}}=\frac{6.7g}{1g/mole}=6.7moles$

Moles of Oxygen = $\frac{\text{Given mass of oxygen}}{\text{Molar mass of oxygen}}=\frac{53.5g}{16g/mole}=3.34moles$

Step 2: Calculating the mole ratio of the given elements.

For the mole ratio, we divide each value of the moles by the smallest number of moles calculated which is 3.33 moles.

For Carbon = $\frac{3.33}{3.33}=1$

For Hydrogen = $\frac{6.7}{3.33}=2.01\approx 2$

For Oxygen = $\frac{3.34}{3.33}=1$

Step 3: Taking the mole ratio as their subscripts.

The ratio of C : H : O = 1 : 2 : 1

The empirical formula for the given compound is CH_2O

For determining the molecular formula, we need to determine the valency which is multiplied by each element to get the molecular formula.

The equation used to calculate the valency is:

$n=\frac{\text{Molecular mass}}{\text{Empirical mass}}$

We are given:

Mass of molecular formula = 180.2 g/mol

Mass of empirical formula = 30 g/mol

Putting values in above equation, we get:

$n=\frac{180.2g/mol}{30g/mol}=6$

Multiplying this valency by the subscript of every element of empirical formula, we get:

$C_{(1\times 6)}H_{(2\times 6)}O_{(1\times 6)}=C_6H_{12}O_6$

Or,

$6\times (CH_2O)=C_6H_{12}O_6$

Hence, to form the molecular formula, we need 6 units of empirical formula

Answer from: Quest

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Answer from: Quest

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Chemical analysis of an organic compound found the following composition: 40.0% C, 53.5% O, and 6.7%...

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