Question

IV] Four Marks

Questions:

1. The percentage composition of an organic compound found to contain 39 9% carbon, 6.7% hydrogen and the rest is oxygen. If the molecular ma of the compound is 60, determine the molecular formula of the compound, Atomic mass of H-1, C-12, 0-16] (F-15)​

Answer 1

Solution :-

Given :-

Percentage composition of carbon = 39.9 %

Percentage composition of hydrogen = 6.7 %

Percentage composition of oxygen = 100 - ( 39.9 + 6.7 )

                                                           = 100 - 46.6

                                                           = 53.4

We know :-

Atomic mass of carbon = 12 g

Atomic mass of hydrogen = 1 g

Atomic mass of oxygen = 16 g

$\bullet \sf \ No \ of \ mol \ of \ carbon = \dfrac{39.9}{12}=3.325 \\\\\bullet \ No \ of \ mol \ of \ hydrogen = \dfrac{6.7}{1}= 6.7\\\\\bullet \ No \ of \ mol \ of \ oxygen = \dfrac{53.4}{16}= 3.336$

Simplest ratio :-

$\longrightarrow \sf \dfrac{3.325}{3.325} \ : \ \dfrac{6.7}{3.325} \ : \ \dfrac{3.336}{3.325} \\\\\longrightarrow 1 \ : \ 2 \ : 1$

$\sf Empirical \ formula = CH_2O$

Empirical formula mass = 12 + 2 × 1 + 16

                                       = 12 + 2 + 16

                                       = 30

We know :-

$\bf Molecular \ formula = n \times Empirical \ formula$

Here,

$\longrightarrow \sf n = \dfrac{Molecular \ mass}{Empirical \ formula \ mass} \\\\\longrightarrow n = \dfrac{60}{30}\\\\\longrightarrow n = 2$

Molecular formula :-

$\longrightarrow \sf 2 \times (CH_2O) \\\\\longrightarrow C_2H_4O_2$

$\boxed{\bf Molecular \ formula = C_2H_4O_2}$

Answer 2

Explanation:

Given :-

Percentage composition of carbon = 39.9 %

Percentage composition of hydrogen = 6.7 %

Percentage composition of oxygen = 100 - ( 39.9 + 6.7 )

                                                          = 100 - 46.6

                                                          = 53.4

We know :-

Atomic mass of carbon = 12 g

Atomic mass of hydrogen = 1 g

Atomic mass of oxygen = 16 g

Simplest ratio :-

Empirical formula mass = 12 + 2 × 1 + 16

                                      = 12 + 2 + 16

                                      = 30

We know :-

Here,

Molecular formula :-